Categories
WW1 French Prototypes

Renault Char d’Assaut 18hp – ‘Renault FT’ Development

ww1 French TanksFrance (1915 – 17)
Light Tank – Around 3,500 Ordered

When the Republic of France entered World War 1 on 3rd August 1914 against the German Empire, few could have had any concept of the scale and duration of the war which was to follow. Having already fought the nascent German Empire in 1870-1871 and lost the territory of Alsace-Lorraine in a humiliating defeat, France was determined not to repeat its failures, yet entered WW1 unprepared for a new type of warfare dominated by artillery and rapid-fire machine guns. Just as other nations soon found, the men of their respective armies, regardless of personal heroism, were no match for a well-prepared defense or machine gun fire. Machines were to be a key to victory, new armored machines carrying guns to meet the enemy and, to this end, France developed a tank which was to shape their future designs for many years and become an icon of WW1 – the Renault FT.

Background

The Republic of France was to suffer appalling casualties in WW1. The Western Front, large swaths of which cut through Eastern and Northern France, was the scene of some of the bloodiest fighting ever seen in Europe and was brutal grinding butchery for four years from 1914 until 1918.

Despite numerous assaults by the British, French, and Germans on the Western Front, neither side could gain an advantage, and the war descended into a static war of attrition, with troops having to shelter below ground from the murderous effects of artillery and machine gun fire. The industrialization of Europe had created the situation where artillery and machine guns could bring warfare to a standstill and the military tactics of the belligerents had not adequately kept pace with technology.

Just as modern technology and industrialization had created the circumstances for the static war, they also held out the prospect of a solution for it as well. Automobiles and aircraft were in their infancy, but were rapidly turned to war uses and armored cars had actually been in development in many nations prior to the war. It is no surprise then that, with the slaughter taking place in Europe between the Great Powers, as armored cars could not traverse the shattered ground, tracked vehicles were considered by Britain, France, and Italy (suffering its own stagnant warfare on its northern front against Austria-Hungary) all around the same time.

Tracks to get over the broken ground would then need armor to protect the crew, and weapons to bring the fight to the enemy. The concept of what was to become the tank was an inevitability, but these allied powers had little in the way of coordination in the early days of the war, and each ran their own programs with varying degrees of success.

A French Solution

Unlike the British, who by 1915 had abandoned the Holt track system, and by the end of the year abandoned other ‘low-slung’ types of track in favor of an ‘all-round’ system, the French were still looking at the Holt system for their own designs. There was some parallel development in France, with some work on machines such as the Schneider CA1 and St.Chamond, but one man stood out with a different view, that of a smaller machine better suited to the conditions on the front lines.

The man behind all of this was the French ‘Father of the Tanks’ (French: ‘Père des chars’), Jean Baptiste Eugene Estienne (1860 – 1936). With an aptitude for mathematics and science, he had joined the French Army in 1883, becoming an artillery officer. By the start of WW1, Estienne was a Colonel commanding the 22nd Artillery Regiment in combat.

With a first-hand experience of the power of modern weapons, such as his own artillery, but also witnessing the devastation from machine guns, he rapidly saw the need for some kind of protective shield. By the middle of 1915 (at a time when the British were already working on what was to become Little Willie), Col. Estienne learned of a tracked barbed-wire cutter based on the Holt chassis and developed by Eugene Brille of the Schneider Company.

It was not much of a logical extension for Col. Estienne to consider this as a suitable vehicle on which to mount some armor. His efforts failed though until December 1915, when he finally convinced Marshal Joseph Jacques Cesaire Joffre (1852 – 1931) of the validity of his idea.

Unknown to Col. Estienne at the time was that Schneider had already been developing its own vehicle with exactly the ideas he had in mind; armor and a gun on the Holt chassis. That tank became the Schneider CA-1 and Col. Estienne witnessed trials of that vehicle on 9th December 1915. The Schneider design had some very serious shortcomings, not least of which was the mounting of the main gun in a peculiar fashion on the side of the machine, seriously limiting its combat potential.

The engineering-orientated mind of Col. Estienne must have been triggered into action by this experience, as on 21st December 1915 (the day the Schneider CA-1 was authorized for production), he reached out to the famous industrialist Louis Renault (1877 – 1944) with his own ideas for a better vehicle – one designed from scratch to do the job rather than just a modified tractor. Monsieur Renault was, at first, reluctant to embark on building a tank, but by the middle of July 1916, he confirmed to Col. Estienne that he was indeed working on a light tank.

The war conditions for France had not improved since 1914, but waiting until the middle of 1916 had now put France well behind Great Britain in terms of tank development. Lagging behind, but now aware of British developments, the French actually tried to convince the British to hold off on using their own tanks for the first time until they were ready with theirs. No doubt, it was a fine idea to have a coordinated approach, but the slaughter underway each day was not abating and the British were anxious to try and break the stalemate which was also costing them so dearly.

Following the British use of tanks in September 1916, the French were now under no illusions about the true potential of these new weapons and, on 30th September 1916, Colonel Estienne, as the most senior French officer with the knowledge, interest, and experience in such matters, was appointed as Commander of the newly formed French armored corps, known as the ‘Artillerie Speciale’ (English: Special Artillery).

Conception and Development

The idea for a tracked tank had first been brought to Louis Renault’s attention by Colonel Estienne back in December 1915, but he had at first been reluctant to postpone or divert production away from other military work for a new and unproven weapon. By the summer of 1916, however, this view had changed, probably as a result of his factory being subcontracted to produce parts for other firm’s tank designs, although he had been doing some preliminary work on a tank design nonetheless. M. Renault confirmed to Col. Estienne in July that year that he was working on a light tank design, although how much of Col. Etienne’s ideas had to that point been absorbed or used by M. Renault is debatable. What is known though, is that Col. Estienne had been unimpressed by the ‘big box’ tanks and foresaw instead a mass of smaller, light tanks acting like a swarm of bees, overwhelming the enemy with a rapid advance, and multiple weapons delivering fire from all quarters during an advance. The conversation on 21st December 1915 between Col. Estienne and M. Renault showed that what was wanted was a tank of not more than 4 tonnes in weight, a two man crew, a top speed of up to 12 km/h, and a machine gun in a turret on top. M. Renault agreed to produce a wooden mock-up of such a design by October 1916.

This new tank would have to be mechanically simple to ease demands of production, which was already at full stretch for the war effort, be constructed by relatively unskilled labor, as most of the skilled workforce was now in uniform fighting, and be cost-effective. The Army could not afford enormous and expensive vehicles that had so far proven to be somewhat unremarkable, like the Schneider CA-1 and the enormous St. Chamond. Smaller, cheaper vehicles, and lots of them were the order of the day.

The ungainly St. Chamond was well armed but suffered from woeful mobility off-road due to the outdated track system and the size of the projection at the front. Source: Pinterest

M. Renault was director of the Société des Automobiles Renault (Renault Automobile Company), but other key individuals at the firm and connected to it were involved in aspects of the design, such as M. Rodolphe Ernst Metzmaier (industrial designer), and M. Charles Edmond Serre. They were to fulfill Estienne’s vision of small fast tanks within their own manufacturing capabilities and what they developed was to become one of the most famous tank designs of all time, the Renault FT.

“L’audace, l’audace, toujours l’audace!” – A Bold Design

In order to be mass produced, this new tank would have to seize upon the enemy quickly and boldly destroy it with machine gun fire. To do this, it was shorter, narrower, and lower than the CA-1 or its huge cousin, the St. Chamond. Smaller would mean less space for the crew and this was reduced to the bare minimum – just 2 men. One man would drive and the other would command the tank and operate the weapons.

Using a single weapon with all-round fire in a turret was not a new idea by any means, and was already in widespread use on armored cars, and even on Little Willie and some earlier British designs, although the British later switched to side-mounted guns instead. The key advantage of a turret, as used for this little French tank, was that it concentrated firepower in one place, for one man, which allowed the tank to remain small and yet carry useful firepower for the assault. A turret was quite simply the only practical solution to the problem of providing fire to all sides on a light tank. This was realized by the British for their own ‘light’ tank, the Medium Mark A Whippet, which started development in December 1916 and which, in its early form, was the ‘Chaser’ and had a single turret for firepower. Whereas that turret was abandoned in favor of multiple machine guns all round in a large casemate, the Renault was too small for that to be an option, so it was a turret or nothing.

A British Medium Mark A ‘Whippet’ passing a group of German prisoners of War on the Western Front. Source: US National Archives

With the driver placed in the front, the commander/gunner sat behind him to operate the turret and weapon, and the engine at the back, the Renault FT is seen by many as being the first ‘modern tank’ although such comparisons are superficial at best. The most important part of this Renault tank is often ignored by historians and was, in fact, the separation of the engine from the crew. The British tanks, for example, did not do this vital safety-step until the Medium Mark B in 1918, and neither the French Schneider CA-1 nor the St.Chamond did this either. The bulkhead protected the crew from the stifling heat and fumes of the engine and, perhaps more importantly, from potential engine fires.

The Schneider CA-1 had a most unusual arrangement of the primary armament off to one side but was more hampered by a general lack of mobility. Source: Public Domain

M. Renault finished his wooden mock-up on schedule in October 1916 and showed it to Col. Estienne. This design set the basic layout for the vehicle over its life, although each part was subject to changes at one point or another. For this wooden mock-up, the turret was nothing more than a simple cylinder with the only armament. Stood inside the tank, with his head and shoulders inside the turret, was the commander/gunner who could use a hatch in the turret to climb in and out. The driver, however, sat at the front, would have to use a hatch on the front deck of the tank, a very dangerous prospect for him if he had to get out facing enemy fire.

Original wooden mock-up for the Renault FT with the cylindrical turret and side removed, showing the internal arrangements. Source: tankandafvnews.com, colorised by Jaycee Davis

Perhaps the biggest hurdle to the development of the FT was not the relative merits or deficiencies of the design, but the French military mindset. For a big battle, it was logical that a big assault, a big gun, or a big weapon was the solution and the concept of small, light tanks was perhaps incongruous in the face of the large British tanks and the no less huge St. Chamond.

The prototype was tested and, despite some reservations, was accepted for service in May 1917, when Marshal Henri Philippe Pétain (1856 – 1951) replaced General Robert Georges Nivelle (1856 – 1924) as Commander-in-Chief of the French Army following the disastrous Nivelle Offensive and French Army mutinies. Marshal Pétain was an advocate for the use of tanks, supportive of Estienne, but also with an eye not just to its potential as a weapon but also as a morale booster for the war-weary infantry who were bearing the brunt of the fighting. Later, he was to order that all of the trucks carrying these tanks to the frontline have written in large characters on their backplate “Le meilleur ami de l’infanterie” (English: ‘infantry’s best friend’).

Brigadier-General Leon Augustin Mourret (1849-1933) though, Director General of the Motor Services, was reluctant to adopt the Renault design which, at the time, was being developed under the working title of char mitrailleur (English: machine gun vehicle). He was likely conscious of interfering with the production of other equipment such as trucks, tractors, and artillery.

A new mock-up char mitrailleur was presented on 30th December 1916 to the Consultative Committee of the Assault Artillery. Gen. Mourret remained unimpressed, however, despite no longer being the Minister in charge, complaining the vehicle was too light, with the center of gravity too far back, making it unstable, and that there was inadequate ventilation for the crew. Other suggestions included a wider hull and turret, and storage for up to 10,000 rounds of machine gun ammunition (‘normal’ carriage was just 1,820 rounds).

The basic design from October 1916 had been set but there were still deficiencies. The cylindrical turret for the commander/gunner, who had to do both jobs simultaneously, was only fitted with crude vision slits making for very limited observation of the ground around the tank. The body of the tank was a large riveted box with a bulbous back end housing the engine. At the back of this body was a small starting handle for the engine and there was a small air intake on top.

The suspension changed little from the prototype to production, although the vertical spring in the center of the suspension which connected to the arm holding the return rollers was removed for production as it had little value.

Wooden mock-up showing the very large body at the back of the tank and the cylindrical turret. Source: Public Domain, colorised by Jaycee Davis

The arrangements of the body and turret were not ideal and wasted space and weight, both of which were critical. By December 1916, significant modifications to both had been made. The hull’s back was cut much shorter, saving a lot of weight, and the small cylindrical turret was replaced with a much wider hexagonal one with a cross-shaped vision slit in each face. The turret also overhung the side of the hull, necessitating small flanges to be attached to the hull to cover the bottom of the turret where it projected. All of the plates used in this revised design were flat and to be made by riveting to a steel frame inside the vehicle.

Rodolphe Metzmaier with the revised, December 1916 FT. Note that the armament is a single machine gun, the shadow of it on the wall behind it is misleading. Source: arquus-defense.com, colorised by Jaycee Davis

Some of the suggestions from the December 1916 examination were acceptable to the design team, but others were clearly impractical. The Consultative Committee of the Assault Artillery then voted on production; the vote was seven-to-three in favor of production and orders for 100 char mitrailleurs followed. That order was increased in February 1917 to 150 vehicles, although Col. Estienne had been pressing for orders for 1,000.

The FT-17 That is Not

It is important to note that the name ‘FT’ was never an abbreviation or acronym, despite numerous books and websites claiming explanations for the initials including ‘Faible Tonnage’ (English: ‘low tonnage’ – ‘light weight’) or ‘Franchisseur de Tranchées’ (English: ‘trench crosser’). The name ‘FT’ was none of those, it was just a factory code for this char mitrailleur, nothing more, nothing less. All the Renault tank products were issued with a two letter code serving to identify and differentiate them. FT simply followed FS, and would, in turn be followed by an FU (which was later used for a heavy Renault lorry), then FV.

The Renault FT is also often referred to as the ‘FT17’ or ‘FT-17’, although this specific naming was never acknowledged by Renault or any official working on the project. The ‘17’, of course, was in connection to the year 1917, as it was customary for many French weapons of the time creating the ‘char leger Renault FT modèle 1917’ (English: Renault Fast Tank Model 1917). The ‘FT-17’ designation though, was only later referred to, after the war. For the duration of WW1, it was simply the Renault FT for convenience.

Prototype

A single prototype vehicle for this new version of the FT was delivered in January 1917 and performed first trials at Renault’s factory at Boulogne-Billancourt, before being sent by Col. Estienne to the Artillerie spéciale (English: Special Artillery) proving grounds at Champlieu, North-East of Paris, for final corrections before its official make or break trials in April that year.

If getting an order for a prototype and small production for his light tank idea was a win, then in April 1917, even before the trials, Col. Estienne was triumphant. The Consultative Committee of the Assault Artillery was on his side and voted in favor of his plans for production of 1,000 examples. This triumph was further crowned by General Nivelle, who was not an opponent of tank production, was now a convert to armored warfare and supported this production.

Official trials took place at Marly, South-East of Lille, between 21st and 22nd April 1917. Here, during comparative trials against the Schneider CA-1 and St.Chamond tanks, the diminutive FT was shown to be superior. Perhaps buoyed by his success in winning over General Nivelle and the proof of concept beating any other tank the French had, Col. Estienne then suggested that this machine gun armed tank be fitted with a small 37 mm gun creating a ‘char canon’. It had never been intended to carry anything other than a machine gun until this point, but he felt that a version of the 37 mm modèle 16TR infantry cannon could be made to fit and would provide some useful support to infantry in attacking enemy defences. A machine gun, after all, was almost useless against an enemy bunker, but a small gun could fire explosive shells right where they were needed instead of relying on field artillery behind the assault. There was insufficient space for both a cannon and a machine gun. But, as these vehicles were to be used in groups, they would be able to provide complementary fire for each other, with the char canon taking out the strongpoints and the ‘char mitrailleur’ taking out the infantry.

Reservations

General Nivelle might have been converted to the value of the tank, but M. Albert Thomas was not to be convinced. The small space inside the turret effectively limited it to a commander not more than 1.68 m tall (5’6”). This, combined with concerns over the instability of the vehicle, the ventilation for the crew, inadequate ammunition capacity, and the difficulty of one man commanding and operating the gun, led to him suggesting an additional crew member be added to operate the main armament. The addition of a third crew-member would mean a total redesign of the vehicle to accommodate him, but would in fairness have solved a problem that was to plague French tanks for a generation, the tiny one-man turret.

Regardless of his concerns, right or wrong, it was too late. General Nivelle’s offensive on the Chemin-des-Dames was an utter failure, with great loss of life, and further delays to a tank program were no longer acceptable. M. Thomas though, left on an overseas trip, and in his absence, Col. Estienne simply worked around him. He demonstrated the tank for officers from the disastrous Chemin-des-Dames offensive, including those who had fought with the Schneider and St.Chamond tanks in what was France’s first use of tanks – they were convinced. Their insistence and the political pressure of a failure to break the stalemate on the Western Front now persuaded even the reluctant General Mourret that they were needed urgently, and he overruled M. Thomas’ order. The original order for 1,000 vehicles was replaced with a new order for 1,150 vehicles, consisting of 500 of the original char mitrailleur armed with the 8 mm Hotchkiss machine gun and 650 of the new char canon fitted with the 37 mm gun.

Pétain, the advocate

Marshal Pétain, himself an artillery officer, knew Colonel Estienne and had, in general terms, agreed on the need for tanks and that small, fast tanks could overwhelm an enemy unlike the large and slow Schneider CA-1 and St. Chamond. In a brutal war of attrition, production played a part too, and the tiny FT had a small manufacturing footprint. Five FTs could be built for every heavy tank and those heavy tanks were not armored sufficiently to stop German artillery fire. Instead of armor then, these small tanks would rely on their small size and good mobility to avoid enemy fire. Pétain did not need much additional convincing post-Chemin-des-Dames and increased the order from 1,150 to 3,500 vehicles instead. The design undoubtedly had significant flaws but it had a single massive advantage over every other design available – it worked. Rather than wait on new and improved design Pétain made use of what he had, a working design, and one intended for a new offensive in Spring 1918.

To smooth out production, the hurdle that was M. Albert Thomas was removed too, replaced in September 1917 by the Under Secretary of State for Artillery and Munitions, industrialist M. Louis Loucheur (1872 – 1933). Nothing was going to get in the way of Pétain’s new tank. So when, shortly after placing this order, it was found that Renault would not be able to produce all these vehicles itself in time, Renault waved any patent rights issues, allowing production to go to other factories. Contracts were eventually issued to Berliet, Somua, and Delaunay-Belleville as well as consideration of production outside France in Italy and the United States in order to produce the numbers demanded.

Conclusion

The development phase of the Renault FT, one of the most identifiable and famous tanks of all time, had concluded. The vehicle would undergo significant modifications and trials with various nations and see action beyond WW1 in many theatres. It was not a perfect tank by any means, the tiny one man turret, the front access for the driver, the lack of a radio, and the relatively weak armament would plague the vehicle and its many variants, but the design was to prove the most successful French tank of WW1 even if it nearly never happened at all.



Illustration of the 1916 design of the FT produced by Yuvnashva Sharma, funded by our Patreon campaign.

Sources

Renault. (1917). Renault Char d’Assault 18hp.
Canon de 37 SA pour Chars Légers 1918
Lt. Goutay. (1920). Manuel pratique du Char Renault
War Office. (1922). Instruction sur l’arrimage du lot OI RI des Chars Légers Renault
War Office. (1931). Instruction sur l’Armement et le Feu dans les Chars Légers
War Office. (1935). Instruction sur l’Armement et le tir dans les unités de Chars Légers
Bruché, Col. (1937). Manuel d’Instruction pour les Unités de Chars Légers – Canon de 37 SA –
Gale, T. (2013). The French Army’s Tank Force and Armoured Warfare in the Great War. Ashgate Press, England
Vauvallier, F. (2014). The Encyclopedia of French Tanks and Armoured Fighting Vehicles 1914-1940. Histoire and Collections Publishing, France
Zaloga, S. (2010). French Tanks of WW1. Osprey Publishing

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Categories
Coldwar American Prototypes

120mm Gun Tank M1E1 Abrams

USA (1979 – 1985)
Main Battle Tank – 14 Built

Following the failure of the MBT-70/KPz-70 joint project, the need for a new tank for West Germany and the USA (amongst others) had not gone away. One of the main points of value for those projects was the interchangeability of parts and, even after the joint project had been terminated, the desire for more interchangeability continued. In 1974, a memorandum of understanding (MOU) was signed between the USA and West Germany in which the USA would test the German Leopard 2 with the goal of standardizing as much as possible between the two tank programs. This was followed, in 1976, by an addendum to that 1974 MOU in which the components to be standardized were identified.

It was here that the decision was made to select the German 120 mm smoothbore gun for both tanks, although it was apparent that the first series of M1 Abrams entering production would have to be armed with the M68 105 mm gun (an American-made copy of the British L7 rifled gun) instead, as the 120 mm was not ready. In 1976, the project to up gun the M1 with this 120 mm smoothbore gun was already set out, naming this first variant as the M1E1 (E = official Experimental version).

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Experimental Model Number 1

Not only was this first experimental modification of the M1 Abrams going to mount and test the German 120 mm smoothbore, but there were other plans too. Every vehicle has a certain amount of ‘growth potential’ – the amount which it can reasonably be expected to take and accept changes, modifications, adaptations etc. to meet future threats and stay up to date. The same is also true with the M1. Although M1E1 plans had been started in 1976, it was not until February 1979 that this growth potential investigation began with the M1E1 Block Improvement Program starting. This four-point plan was to investigate armor improvements to the front of the turret, a hybrid NBC system incorporating a micro-climate crew cooling system, weight reduction, and upgrades to the suspension and final drives. It was debated about adding an independent thermal imaging sight (CITV – Commander’s Independent Thermal Imager) for the commander for the M1E1.

M1E1 turret showing what appears to be a mockup fitting of the CITV system. Whilst this was not adopted, a small hatch was made on the roof of the M1A1 so it could be added later. Source: US DoD

Adding a CITV would have given the M1E1 commander the ability to adopt an independent hunter-killer mode, able to hunt for targets even whilst a target was already being engaged by the gunner. Due to the expense involved with thermal imagers, this idea was dropped to save money. A circular port was planned to be added to the roof though so that a thermal imager could be added at a later date. The rest of the work was approved in May 1982 for work to proceed with the first M1E1 expected in 1985. The first 2 of the 14 M1E1s were delivered for testing in March 1981, ahead of the actual implementation date of the product improvement program.

“The M1 is now in procurement, with a small amount of development and testing yet to be accomplished. We have procured over 780 tanks as of the end of 1982. Fielding began in 1981 and will continue for a decade or more. The 120mm-gun-equipped M1E1 is now in development. The first production model M1E1 will be produced in 1985. In addition, the Army is pursuing a product development program to assure the M1 maintains its competitive position through the 1980s and beyond”

– US Dept. of the Army, 1983

M1E1 first pilot model built in March 1981. Note the wide ring fitted around the rear sprocket in an effort to prevent it from throwing tracks. Source: Hunnicutt

Blocks

Upgrades made to the basic M1 for the new M1E1 were identified as Blocks. Block I was to consist of the 120 mm gun and NBC system. Block II, which included further improvements in survivability and fire control, would not be done until the M1A1 was in service.

Upgrades – Turret M1 to M1E1

Even before production of the M1 was fully underway, there were concerns over the choice of armament, as the United States’ major NATO allies, Great Britain and Germany, were already fielding 120 mm guns (rifled and smoothbore, respectively) on their new main battle tanks. The brand new US tank was, therefore, going to end up being fielded with the cheap and effective 105 mm and was thus going to be under-armed. More to the point though, the M1 was not going to meet the requirements of the interoperability agreement with Germany which had called for the use of the 120 mm German smoothbore. Knowing that this gun would be fitted eventually, the turret was at least designed with this gun in mind. As the turret was going to have to be upgraded anyway with better armor, it was decided to incorporate some other, smaller changes too. Firstly, the amount of stowage was improved with an additional stowage box added to the turret side. The second stowage improvement was the addition of a full turret bustle rack on the back in which items could be stowed. This replaced the original canvas strap system which was slow and cumbersome to use. The final change to the turret, other than the gun and armor, was the wind sensor. On the M1 turret, the wind sensor, in the middle of the turret at the back, could be folded down. It was now fixed in place on the M1E1 turret.

Visual changes between the M1 and M1E1 turrets. Note that this graphic shows a 3-section ammo blow-off panel on the M1 rather than the original 4-piece panel. Source: Mesko

Armament M1 to M1E1

The M68A1 105 mm gun was cheap and reliable and the M1 carrying that gun could carry 55 rounds of ammunition between the hull and turret compartments. Upgrading to a larger gun, as had been considered, would reduce the amount of ammunition which could be carried. With Great Britain and Germany fielding powerful 120 mm guns on their new main battle tanks (Challenger and Leopard II, respectively), this left the US in the position of not just using a less powerful gun but having no cross-compatibility in terms of ammunition with either NATO partner.

The German 120 mm smoothbore, made by Rheinmetall, had suffered from some development issues and was not delivered for testing to Aberdeen Proving Grounds until the first half of 1980, where it was designated as the XM256. Plans for an American-designed breech for the gun were still on the table, as it was felt that the German breech was too complex and the source of some additional problems. Those new-breech plans were abandoned as unnecessary and the German breech would be used instead, as the problems were steadily overcome and simplified. Following successful trials of the XM256 in 1980, the first 14 M1s were retrofitted with this gun replacing their 105 mm rifled guns. As such, these vehicles were designed M1E1 to test the new gun mount and other improvements. When the XM256 120 mm smoothbore gun was accepted for service for the M1A1, it was redesignated as the M256.

The early problems with the German 120 mm Smoothbore made by Rheinmetall had led to the idea that it might not be ready at all. As a result, a secondary armament upgrade was considered, using an enhanced 105 mm gun in March 1983. This would have used a gun tube 1.5 metres longer than the tube of the M68A1 105 mm gun, and which could tolerate a much higher internal pressure. When the problems with the 120 mm XM256 were resolved, there was no need for this improved 105 mm gun and the plan for it was dropped for both the M1E1 and IPM1. The XM256 was accepted for use in December 1984, although into FY1985 there was still a validation trial of the improved 105 mm gun on an Abrams listed briefly as M1E2. Regardless of this 105 mm gun though the development life of the 105 mm rifled gun was essentially over, the new gun was clearly going to be the 120 mm smoothbore.

As the turret had been designed from the beginning for this larger gun, mounting it in the turret was not a big problem, although the amount of ammunition would be reduced to just 44 rounds.

The German 120 mm smoothbore adopted for trials as the XM256. This gun is using the German breech which was initially felt to be too complex. The idea of a simpler American-designed breech was dropped and this gun was adopted later as the M256. Source: Hunnicutt

These 44 rounds were planned to be divided amongst the turret bustle (34) and hull rear (6), with an additional 4 (‘ready rounds’) in an armored box on the turret floor – a hangover from the M1. With the size of these unitary 120 mm cartridges though, those extra 4 were eliminated, leaving just 40 rounds for the tank. The hull stowage (6 rounds) was retained in the rear of the hull (accessed by a small door in the bottom right of the turret basket), albeit with a new size rack for the larger rounds and an improved hatch on the armored door. In the turret, the ammunition rack also had to be changed for the new, larger rounds with the shells divided into three sections in the bustle. Each of the outer sections could hold 9 rounds and the center section, divided from the other two alongside it by a bulkhead, held the main stock of rounds, with 16 more. The original blow-off panels above this ammunition store consisted of four rectangular sections on the first M1s, changed to a three-section panel, with two narrow sections surrounding a slightly wider center panel, on the M1E1. When the M1E1 was adopted as the M1A1, this 3-section panel was dropped and replaced with a simpler 2-section blow-off panel instead.

Elevated front and rear view of the pilot model M1E1, providing an excellent view of the changes to the blow-off panels and stowage on the turret. Note that, at this time, the circular panel where a thermal imager could be fitted had not yet been added. Source: Hunnicutt
Visual differences between the turret front and armament of the M1 compared to M1E1. Source: Mesko

The switch to this new, heavier and larger caliber gun also meant changes to the fire control system were needed. A new gearbox for elevation and depression of the gun, software upgrades and electronics were added in order to make this new gun workable. The coaxial gun needed some minor modifications, with a new mount for the ammunition box, feed and ejection chute, and a box to collect spent ammunition and links.

.

Mobility

One consideration to upgrading mobility was to reduce weight. Simultaneously with increasing the size (and weight) of the main gun and the addition of more armor (and weight) to the turret, there was an attempt to reduce the weight of the primary construction elements of the tank. There would, in later years, be numerous ‘lightenings’ of components for the Abrams throughout its life to save a little weight here and there, but in 1985 the idea was to take the single largest and heaviest element, the hull, and make it lighter. The hull, which was of an all-steel welded construction, offered few options for lightening, so the project was switched over to the concept of making a completely new hull for the M1 out of composite materials. Those plans, therefore, formed no part of the M1E1 or the M1A1 by the time it was approved.

The other mobility upgrades were dictated by the increased weight. Improved final drives and transmission for the M1E1 would increase reliability and deal with the additional load. Further, new suspension shock absorbers were fitted to the front to increase the damping effect. Less obvious was the adoption of a slightly modified road wheel with a thinner rubber tyre and wider cross-section (132 mm to 145 mm).

NBC

Somewhat surprisingly for a modern main battle tank designed to fight a modern war in Europe, which was highly likely to involve the use of nuclear, chemical, or biological weapons, the M1 Abrams had no NBC filtration system. The crew, instead, would have to wear their personal protective equipment, such as gloves and respirators, whilst fighting in the tank – an enormous encumbrance for them which would reduce their fighting ability. A key goal of the M1E1, therefore, was the addition of an NBC system which would create an overpressure within the tank to keep out contaminants and poisons, with filters being used to scrub the air being drawn in.

Port for the NBC system trialed on the M1E1, as it appears on the left side of the hull. Note: the turret is turned to the rear in the photo. Source: Hunnicutt

One M1E1 was modified for these purposes and for testing at the Natick Laboratories in Maryland. Fitted with the M43A1 detector and AN/VDR-2 radiac (mounted on the turret floor), even very low levels of chemical or nuclear agents could be detected. The M13 filtered air system, which delivered air directly to the crew’s face masks as was used on the original M1, was retained as a backup system.

The system was to use an all-vehicle air conditioning system (macroclimate) instead of the alternative of using individual crew cooling systems (microclimate). This macro system would keep the crew comfortable inside the tank as well as filter the air coming in. However, this cooling system proved to be bulky, as it had to filter, cool, and circulate the air around the tank. The crews who took part in the testing (two crews from 2nd Battalion 6th Cavalry) were positive about the need for the new air system, but in light of the bulk and expense involved, it was decided to abandon the tank-climate system and revert to the earlier idea of a microclimate individual crew-cooling vest instead.

Other

Other minor changes incorporated at the same time as the others were a slight rearrangement of internal stowage, the addition of a dual air heater, a new hull electrical network box, and new electrical harnesses. Minor changes continued in the turret, with a rerouting of the electrical harnesses and alterations to the commander’s seat and a new knee guard for the gunner.

With a new and improved M1 underway for the Army (which would enter service as the M1A1), it was also a potential replacement tank for the United States Marine Corps (USMC), who were still using the venerable M60 series tanks. To meet the needs of the USMC, the M1A1 would have to be able to ford deep water, up to 2 metres deep. This meant that a deep water wading kit had to be designed, fitted, and trialed on the M1E1. These trails were carried out in October 1984.

Design for a deep water wading kit for a USMC version of the M1A1 which was evaluated on the M1E1. Note: after leaving the water the turret would be traversed and knock off the towers over the air inlet and exhaust. Source: Hunnicutt

Trials

By 1984, the M1E1 was undergoing Development Test II and Operational Test II, making sure it met the requirements of the Army. The M1E1 was expected to enter production in 1985, when it would be renamed from M1E1 to M1A1. At the same time, the Army was also pursuing a program of continuing product improvement with an eye to changes and development of the M1 Abrams as a platform to meet future threats.

Montage image of M1E1 with deep wading kit fitted during trials in October 1984. Source: Hunnicutt

Before these trials were over, the Improved Performance version of the M1, known as the M1IP, was authorised and would provide a stop-gap whilst the new M1A1 entered production. The IPM1 though did not adopt the German 120 mm gun or the NBC suite trialed on the M1E1.

A sequence of shots showing an M1E1 from above during tropical trials in Panama. Source: US National Archives
M1E1 Abrams with turret traversed to the rear. Source: Mesko
One of the 14 M1E1s as fitted with the XM256 120 mm smoothbore gun and other improvements, including substantial slabs of steel welded to the hull and turret front to mock up the weight of a new armor package. Source: Mesko
Pictured in 1984, this M1E1 is being evaluated. The additional plating on the front of the turret is readily apparent. Source: Zaloga

Armor M1 to M1E1

The most obvious changes to the M1E1 from the M1 are the new, larger gun and the large slabs of steel welded to the front of the turret. It is important to note that although these were large slabs of steel welded to the front that they were not actually additional armor in of themselves. They were added simply as weight to simulate the additional weight of the new composite armor modules being added behind the original ‘skin’ on the front of the turret. The structure and arrangement of this armor is known, although the exact composition of those special armor arrays is not. The composition of the armor is still classified, although it is known that, at this time, the Abrams was not using Depleted Uranium (DU) within the armor. This was not added until later. Nonetheless, the ‘special’ armor provided significantly better protection (weight for weight) than conventional cast-steel or rolled steel armor, making use of composite materials and spacing within the arrays. This was particularly effective against High Explosive Anti-Tank (HEAT) ammunition and less so against Kinetic energy ammunition (APFSDS – Armor Piercing Fin Stabilised Discarding Sabot).

A careful look at the front of the turret of one of the first M1E1s being evaluated clearly shows that these slabs (eventually three-thick) were added incrementally to the design during evaluation. With all of the modifications to the turret and hull, the new gun, and the additional armor, the M1E1 weighed 62 tonnes. The M1 would get even heavier throughout its life in service, far exceeding the original goals of the 1970s.

This early M1E1 during testing provides a rare view of the additional plating on both sides of the turret face. Source: Hunnicutt
Two views of two of the 14 M1E1s fitted with the XM256 120 mm smoothbore gun and other improvements, including substantial slabs of steel welded to the hull and turret front to mock up the weight of a new armor package. Note that the application of welds differs for each vehicle. Source: Mesko (right) and unknown (left)

Conclusion

The M1E1 was a very successful trial project. Even though not all of the systems proposed or tested, such as the commander’s independent thermal sight, were adopted on the M1A1, the M1E1 marked the step into what the M1 was supposed to be in the first place – a superior tank in all aspects to the Soviet tanks it faced for the 1980’s in Western Europe. The M1 ceased production in January 1985, as new vehicles would be of the new M1A1 standard. The only aberration to the story of the M1E1 is the appearance of the IPM1, a stopgap M1 to meet the urgent need for more protection.

The M1E1 also marked the first step in what was to be a significant gain in weight for the Abrams, a trend which has continued since then, as the demand for protection has increased as the threats the tank faces change. The M1E1 is not a well-known variant of the Abrams and it never saw combat. Just 14 were made for testing and none are known to survive.



Illustration of the 120mm Gun Tank M1E1. Produced by Tank Encyclopedia’s own David Bocquelet.

Specifications

Dimensions (L-W-H) 9.83 x 3.65 x 2.89 meters
113.6” h (1984 memo)
311.68” long (1984 memo) – L W H all identical to M1 hull
143.8: wide (1984 memo)
Total weight, battle-ready 62,000 kg (62.9 US tons -1984 statement) 63 tons – 1984 memo
Crew 4 (Commander, Gunner, Loader, Driver)
Propulsion Avco-Lycoming Turbine (Petrol) 1,500 hp (1,119 kW)
Maximum speed 41.5 mph (67 km/h) governed
Suspensions High-hardness-steel torsion bars with rotary shock absorbers
Armament 120 mm XM256 smoothbore gun
12.7 mm M2HB QCB heavy machine gun
2 x 7.62 mm MAG58 general-purpose machine guns
Armor Hull: Welded steel with special armor inserts in the front. Composite side skirts.
Turret: Welded steel with special armor inserts on the front and sides
Production 14

Sources

Hunnicutt, R. (1990). Abrams – A History of the American Main Battle Tank. Presidio Press, California, USA
Mesko, J. (1989). M1 Abrams in Action Squadron/Signal Publications, USA
Janes Armour and Artillery 1985-86, Janes Information Group
Lucas, W., Rhoades, R. (2004). Lessons from Army System Developments Vol. II – Case Studies. UAH RI Report 2004-1
Organic Composite Applications for the M1/M1A. (1986). Allen Pivett. General Dynamics Land Systems, Michigan.
US Army Research Institute of Environmental Medicine. (1991). A Physiological Evaluation of a Prototype Air-Vest Microclimate Cooling system. United States Army Medical Research and Development Command, Natick, Maryland, USA
US Dept. of the Army. (1983). 1983 Weapon Systems. US Dept. of the Army, Washington D.C., USA
US Dept. of the Army. (1984). 1984 Weapon Systems. US Dept. of the Army, Washington D.C., USA
US Dept. of the Army. (1985). 1985 Weapon Systems. US Dept. of the Army, Washington D.C., USA
US Dept. of the Army. (1984). Army Modernization Information Memorandum (AMIM) Vol. 1. US Dept. of the Army, Washington D.C., USA
Zaloga, S. (2018). M1A2 Abrams Main Battle Tank, Osprey Publishing, England


Categories
New Zealand Armor

Mills’ Travelling Motor Fortification and Charging Device / Rapid Travelling Armour Clad Field Fortification

New Zealand (1914-1915)
None Built – Drawings Only

In the history of the development of the modern tank in WW1, a lot of people are aware of the Landships Committee and names like Stern, Swinton, and Tritton – names synonymous with the invention of the tank. Fewer people are aware of Lancelot de Mole, an Australian inventor who had submitted a tracked vehicle design which was ahead of its time and represented a lost opportunity for those developing the first tanks in Britain in WW1. Almost unknown until now are some of the inventors of the ideas which never got taken seriously. One unnamed antipodean inventor had his invention submitted by a friend to the British military before the formation of the Landships Committee in February 1915; Mr. E.C.Evelyn Mills. Whether Mills’ was writing from a ‘friend’ to mean himself or genuinely on behalf of another is not known but this whilst this person’s ideas may seem naive now, especially in light of over a century of armored warfare experience which followed, this 1914 concept was, if anything, modest. As Mills failed to name his friend and was asking for a substantial sum of money it is perhaps more likely that he was simply writing on behalf of himself. Consigned to being forgotten by history, all that is left of Mr. Mills’ work lies in just three surviving pages of text in the files of the British Ministry of Munitions. What they contain though is a rare glimpse into an early idea for armored warfare and one which, unlike De Mole, has had no recognition until now.

First Contact

On 16th October 1914, Mr. E.C. Evelyn Mills wrote from the Royal Colonial Institute, Northumberland Avenue, London, to Lieutenant Colonel G.N.H. Barlow, an experienced artillery officer. Mills had designed with the assistance of an unnamed friend a vehicle for defeating “the atrocious Prussians”. Lt. Col. Barlow thankfully did not discard the unusual idea from Mr. Mills, but instead passed it on to Col. Louis Jackson, a retired officer of the Royal Engineers. Col. Jackson would later return to service as a General and serve as the head of the Trench Warfare Research Department at the Ministry of Munitions. Col. Jackson then wrote to Mr. Mills, but it was not until 22nd April 1915 that Mills provided more technical information outlining his idea.

Role

One of the key defining problems in the early days of the development of what became known as tanks was what role they were to perform. In 1915, this had started for the Landships Committee as a means to transport a large party of men, protected from German machine-gun fire, over broken ground covered with barbed wire. Effectively, this was what would be known in modern terms as an Armored Personnel Carrier but, in 1915, there was no such name. Later, these carriers changed in role to a vehicle intended for the destruction of enemy machine-gun emplacements instead. In 1914, when Mills submitted his idea, these vehicles were still a long way away both in concept and technology.

Without words such as ‘tank’ with which to name his vehicle, Mills simply defined his new vehicle as a “travelling Motor Fortification and Charging Device” in his initial letter and then, in a follow-up, as a “Rapid Travelling Armour Clad Field Fortification”. Both names give a very clear impression as to what it was that Mills was intending for use from his vehicle. Primarily, the vehicle was to be used to screen soldiers from enemy fire by providing a large mobile shield or “breastwork” for up to 200 soldiers, although, in his April 1915 letter, he changed it to provide cover for 150 men instead.

Mills envisaged a novel form of attack, with some unnecessarily complex ideas for moving the vehicle forwards and backward almost randomly to make targeting by enemy gunners much harder. As the vehicle advanced, it would plough over and through enemy positions, leveling them for the men following. It would advance over enemy trenches up to 10’ to 12’ (3.05 to 3.66 m) wide, a figure more than double the expected 5’ (1.52 m) trench which was set out for the Landships Committee later in 1915. Having crossed the enemy trenches, the vehicle could then turn to follow the lines of enemy defences to clear them of enemy troops but it could also directly assault an enemy gun by charging it and would not have to turn around in order to withdraw from combat. Further to this ‘charging’ idea, the vehicle was also supposed to be able to be used “as a conduit or ram for attacking a Fort, running right up to a wall. Mining or attacking and discharging any kind of explosive, bombs etc, bursting up wall of Forts etc”.

Following the attack on the enemy, the vehicle could also be used to carry wounded troops to the rear or even be used as a transporter for stores and supplies. The internal space was seen as being large enough to accommodate 2 or 3 field guns or military wagons.

Armament

As well as the rifles of the 200 men being carried by this vehicle, Mills also foresaw fitting it with “quick firing machine guns” on the front and sides as well as “larger guns” which were unspecified. Altogether, the firepower for the rifles, machine guns, and ‘larger guns’ across the sides would provide the design with what Mills’ claimed would be a “fearful broadside”.

Design

Sadly, there are no sketches available from Mills’ to show what his vehicle was to look like. If he had sent sketches in with his original letter of 1914, those are now lost, but as none were mentioned in the letter it would appear that there were probably not any at that time. In April 1915, Mills was only suggesting that drawings would be provided if the scheme was approved, which once more suggests that although he may have some sketches none were sent in with the April letter. Again, if any were actually sent in they were not retained with the letter and are now lost. Without those, it is impossible to know exactly how Mills saw his design but he provides sufficient information in his description of the vehicle on which to make a reasonable estimate as to what it may have looked like.

Heavily sloping armor plating across the front, top, sides, back, and bottom was sufficient to stop enemy bullets from injuring the 150 to 200 men inside the vehicle. In 1914, this would have likely resulted in 8 mm to 10 mm of bulletproof plate which was considered adequate prior to the use by the Germans of ‘reversed’ or steel-cored bullets. The sides were to have 120 rifle ports on each side and another 20 or so at each end with a steel or iron shelf for marksmen to lie on when firing, a total 280 loopholes.

Although Mills did not specifically mention side or rear armor, he did allude to it in discussion of the armament and fightability of the design, leaving no doubt that the vehicle was to be completely covered in armor. What is very unclear, however, is his intention that the armor plating should be “hinged and formed [so] that it [the vehicle] can be run into a river with others of its kind and form a continuous Bridge for troops, wagons, artillery, cavalry &c [etc.] to pass across water courses etc.”

With the description of it as a ‘conduit’ as well as a bridge, it would appear that Mills’ design was likely a relatively straightforward box shape rather akin to a medieval siege tower laid on its face and driven forwards. One complicating factor is the description that the vehicle would be able to travel over obstacles up to 8’ (2.44 m) high passing through the vehicle. There is no mention of ground clearance and he provided the dimensions as approximately 37’ (11.28 m) long x 22’ (6.71 m) wide x 11’ (3.35 m) high. If it could traverse an 8’ (2.44 m) diameter obstacle down the middle of the vehicle, this would leave just 3’ (0.91 m) to the roof of the vehicle – not even enough space to sit in. Mills describes the interior fittings as ‘shelves’ though indicating that, rather than having a floor, his design seems to simply forgo the floor and have the man stand or lie on platforms along the sides and inside the front and back. This arrangement would mean that the doors at the front and rear would be upward opening making much clearer how it could work as a bridge, although it would mean that the observation tower would presumably have to be off to one side so as not to prevent troops, horses, guns, etcetera from crossing over the roof.

With doors at the front and back, this would allow the hollow floorless-box to act as the conduit he planned and fitted with a large folding door at the front would allow it to discharge troops for assaulting a position. Mills was also careful to make clear that there was enough space inside to provide a shelter for a 12 lb. gun with its 24’ (7.32 m) gun carriage with enough space for firing.

The unusual arrangement is actually reflected in the early work on the Pedrail landships in 1915 which had also involved consideration of troops carried in a sort of ‘corridor’ along the sides of the vehicle behind armor. For the Pedrail landships, that method of carrying troops was estimated by Colonel Crompton (the contracted expert engineer on the committee) to require 0.49 m2 per man. Mills’ vehicle would (assuming a single-tier floor area on each side) have a floor area of more than double that on the Pedrail landship at 48.17 m2. At 0.49 m2 per man this would provide space for up to about 100 men. Assuming that the 3’ (0.91 m) high area over the central portion of the vehicle could be used for a man lying prone, this would increase the ‘floor’ area of the vehicle to 75.69 m2. A lying man takes up more space but estimating that space as four-times the space of the standing man, this would add a further 13 or 14 men to the total capacity and this may be the ‘shelf’ to which Mills referred. Neither of those floor area figures, however, account for the space which would have to be taken up by the motors, fuel tanks and other components to propel it.

This would perhaps explain the ‘bridge’ idea too, as it would need only be driven into the river and use its hollow shape to create a covered bridge.

At the front and back end of the vehicle was a plough with the intention that this would destroy enemy defences such as earthworks, allowing troops behind to pass through. The vehicle was to be fitted with a wireless telephone for communications. A key feature of the design was the use of a pneumatic telescopic lookout tower 60 (18.29 m) to 100 feet (30.48 m) high, fitted with a searchlight.

Mills’ foresaw an ideal speed as being about 20 to 25 mph (32 – 40 km/h) and estimated (very optimistically) that each vehicle would cost between ‎£4,000 and ‎£5,000.

Power for the vehicle was supposed to come from a pair of 120 hp ‘Daimlers’, which, for a total estimated weight of just 18.5 tons (18.80 tonnes), would mean a power to weight ratio of 6.38 hp/t. This was surely highly optimistic bearing in mind that even Colonel Crompton’s wheeled fort design of February 1915, which was substantially smaller, was going to weigh 24.7 tonnes fully laden with men and guns. Based on this, it seems likely that the weight estimate from Mills’ was far too low and would likely be nearer 30 tonnes, rendering it significantly less mobile than what Mills was proposing.

As the design was effectively two fighting-halves connected by a roof, it appears likely that Mills envisaged one engine on each side driving the wheels. This system would have the significant advantage that the wheels would not have to turn to facilitate steering and it would rely on the skid-steering principle, with direction being affected by varying the throttle to the engine on one side over the other, rather like the way the Medium Mark A ‘Whippet’ was steered. Without actual plans of the vehicle or an explanation of how it was to be done though, this arrangement and method of steering is speculative.

Mills’ vehicle idea had some clear rationale behind it but, as an idea, it was still fundamentally flawed. Despite whatever benefit this engine arrangement may have brought, the vehicle was still wheeled and not tracked. Mills never specified how many axles of what size there were meant to be on the vehicle. The only data provided about the wheels is that they were to have a track width of 10’ (3.05 m), which is the distance between wheels along their axle.

Wheels would mean it was going to create a very high ground pressure under each wheel and that even with multiple wheels it would still produce an excessive loading on a soft surface.

Who was E.C.Evelyn Mills?

The clue to identifying E.C. Evelyn Mills is that he wrote in from Royal Colonial Institute, Northumberland Avenue, London. A check of various registers and legal documents of the period finds that, in 1902, Mr. E.C. Evelyn Mills was the owner of an 1898-built, 15-ton Australian yacht called ‘Rainbow’ registered in Wellington, New Zealand to a local yachting club. This would certainly help to explain some of the features and descriptions, like the tall mast with searchlight, and use of nautical terminology, respectively. The NZ records are also supported by the electoral records from the Royal Colonial Institute in London, showing Mr. E.C. Evelyn Mills of Wellington, New Zealand was first elected there in 1896. Their journal, ‘United Empire’ (1915), also shows that Mr. Mills was elected as a Member of the War Services Committee there in mid-November 1914, which would likely explain his interest in a new type of war machine. Following Mills to New Zealand shows that his full name was Edward Charles Evelyn Mills, born 1857 and died 14th June 1916.

Mills as a character appears to have been reasonably well to do. He has subscribed to contribute money to the war effort yet no doubt he was optimistic after the contact with Col. Jackson about his ideas. Mills even offered to superintend the construction of his own machines for Col. Jackson for the modest fee of 20%. Using his estimate of ‎£4,000 to ‎£5,000, this would have meant a commission of ‎£800 to ‎£1,000 per vehicle.

Conclusion

This design from Mills sounds very similar to the role fulfilled by the first tanks in 1917, smashing their way through enemy wire fortifications to allow troops to follow, but it was also meant to be carrying troops like an armored personnel carrier. Further, it was meant to directly assault gun positions and even forts like an ‘assault’ or ‘heavy’ tank and also to be able to form a bridge-like an AVLB (Armored Vehicle Layer Bridge). So what was Mills’ vehicle? His description as to the possible uses for it covers almost every type of military vehicle from engineering vehicle to tank to ambulance and are really symptomatic of a lack of understanding as to the utility of armored fighting vehicles and of many of the problems with actually fielding such a weapon.

Nonetheless, this vehicle was suggested before there was even a Committee (the Landships Committee) formed to develop a tracked machine. He did not, however, send in a completed idea until the end of April 1915, by which time the Committee had already started work and such ideas as Mills’ were already obsolete. As such, his ideas were simply filed away and forgotten about. Mills died before he ever got to see tanks used by Britain and obviously was not around to even apply for recognition post-war as so many others did. His ideas might have been naive and he might not have lived to see the first use of tanks, but Mills deserves to be recognized as one of the exclusive group who was advocating for armored vehicles in those early years of WW1.

Specifications

Dimensions (L-W) 37’ x 22’ x 11′ (11.28 x 6.71 x 3.35 meters)
Men Carried 150 – 200
Trench 10 to 12’ (3.05 to 3.66 m)
Total weight, battle ready 18.5 tons (18.80 tonnes) more likely ~30 tonnes
Propulsion 2 x Daimler 120hp
Speed 20 to 25 mph (32 – 40 km/h)
Armor Front, Top, Bottom sufficient to stop bullets ~ 8-10 mm thick

Sources

Letter to Col. Barlow from E.C. Evelyn Mills, 16th October 1914
Letter to Col. Jackson from E.C. Evelyn Mills , 22nd April 1915
Lloyds Register of British and Foreign Shipping (Yacht Register) 1902-1903. London, UK
Proceedings of the Royal Colonial Institute, Vol. XXXIX, 1908. London, UK
United Empire, Vol. VI Series I. January 1915. London, UK
New Zealand Times, Vol. LII, Issue 9309. 2nd June 1891 ‘Marriage’
Royal Colonial Institute Year Book 1915. London, UK
Press, Vol. L, Issue 15129 19th November 1914, ‘New Zealand War Contingent Association’
New Zealand Herald, Vol.LI, Issue 15767, 16th November 1914 ‘Expeditionary Force’
Hills, A. (2019). Col. R. E. B. Crompton. FWD Publishing, USA

Categories
WW2 US Other Vehicles

Reno’s Endless Belt Tractor – Underwater ‘Tank’

U.S.A. (1919-35)
Salvage Vehicle – 1 Built

There are not many tracked vehicles designed to work underwater, and whilst these might not fall into the usual category of what people consider ‘tanks’, they are worthy of consideration by anyone serious about tracked vehicle technology. The underwater realm offers challenges unique to vehicles whether they are armed and armored or not.

Jesse Wilford Reno 1861-1947. Source: National Inventors Hall of Fame.

This unusual vehicle was the brainchild of Captain Jesse Wilford Reno (4th August 1861-2nd June 1947), an American inventor from New York, whose most famous contribution to western culture was not a tracked machine, but the escalator, invented in 1899. As an anecdote, his father, Major General Jesse Lee Reno, a Union General in the American Civil War, had Reno, Nevada, named after him. In addition to this, in 1919, Mr. Reno saw an opportunity to put his inventive mind to use; he built an underwater machine designed for salvage operations.

In 1919, underwater operations were still extremely hazardous. The personal diving suit was a huge, clumsy and dangerous affair, and submarines were in their infancy, with numerous accidents still occurring. The depth to which many of these early underwater pioneers could venture was extremely limited and, therefore, salvage at even a nominal depth at the time was impossible. Reno was therefore correct in assessing an important commercial market for a machine able to operate at depth and salvage valuable cargoes from sunken vessels.

The Reno Underwater Tractor being lowered into the water, probably in 1923, showing the drills sticking out of the sides. The heavily riveted construction and narrow, rather crude tracks are readily apparent. Source: Gunning Wrecks, therebreathesite.nl

The Design

The design was a simple one, basically being a sealed and heavily protected cylinder, capable of withstanding external water pressure, mounted on tracks for mobility. Large enough for up to two men, the cylinder measured some 6 feet (1.82 m) in diameter and 8 feet (2.44 m) in height according to the patent. During the recovery of the ‘Scally’, which sank in 1923, the Reno Underwater Tractor was described as being 7 feet (2.13 m) in diameter and 9 feet (2.74 m) tall, weighing some 18 tons (16.3 tonnes).

Air supply was provided by the ‘mother-ship’, which delivered air for the occupants of the vehicle but also compressed air which was to be piped into a large buoyancy sack attached to the sunken vessel or part of it. That buoyancy sack would then rise to the surface for recovery. This is still, to this day, effectively the same means by which things are raised from the sea. The mother ship also provided an electrical supply for the vehicle by means of the same umbilical cable down which air was pumped. This electrical power was used for lighting and also to power the equipment in the vehicle. Vision from inside the machine was limited to just a small glass porthole in each ‘side’ of the cylindrical chamber. Access was only possible via a single circular hatch on the roof of the machine.

Reno’s Underwater Tractor showing a significant problem of track sag.
Source: therebreathersite.nl / tauchtechnik by Hermann Stelzner
Side view of the Underwater Tractor shows a significant change to that in the patent, namely a distinctive raised top run for the tracks. Source: Popular Science: September 1923

For raising a sunken vessel, the machine would simply be used to connect a series of buoyancy sacks along the exterior of the vessel which, once filled with air, would bring the whole ship either to the surface or just off the sea-floor so it could be towed to shallower waters for salvage. Additionally, clever knowledge and use of the tides could be used to raise the ship, move it to shallow water and then resink at high tide, whereby it would be exposed by the receding waters.

Two images from US Patent US1523660 dated 1919 showing the drilling system (left) and compressed air hose (right)

Air Bags and the Cannon

The ‘airbags’ were, in fact, large steel boxes into which the air was pumped, but the question was how to attach these buoyancy devices to the hull of the ship. Each one would be exerting a lifting force of 300 tons, so the connection had to be extremely strong. The solution Reno settled upon was that of hooks which would be fastened into the side of the sunken vessel’s hull.

The question, therefore, was how to make holes in the side of sunken vessels. In his original 1919 Patent, he determined that it should be made by means of a drill rotating within a water-tight coupling. This drilling system though, was after he had already submitted a patent application for the concept of using a gun to make the holes.

Images from Canadian Patent CA225695 showing the means of puncturing the side of the wrecked ships hull and attaching the large vertical floatation units by means of hooks into those holes

The hole would be made by firing a horizontally mounted gun using compressed air. The calibre of this air cannon was given as 4” (101.6 mm) of an unspecified “well-known type” firing a pointed solid steel slug through the outer hull of the sunken vessel to make a hole for the attachment of buoyancy bags/boxes. The barrel of this gun was supported by the walls of the crew chamber through which it was projecting and was fitted with crude ‘stuffing boxes’ acting as the recoil buffers. As drawn, this arrangement was hazardous and likely to violate the watertight nature of any seal around that gun. In his submission, Reno mentions that he considers a gun using the ‘Davis’ principle to balance the recoil of the gun. The shell was only to be fired with enough force to rupture the side of the hull without causing damage to the interior of the ship, although quite how this was to be calculated is unclear. With up to 50 holes needed per side or a hole every ten feet (~3 m) by Reno’s calculations, a large number of projectiles would have to be carried in order to perform this means of hole-making. The fact that a month after this ‘gun’ idea had been submitted he had switched to a drilling system demonstrates that even he understood the impracticality of this underwater cannon concept. When Reno’s machine was used in 1923, it was using not one but two 4” (101.6 mm) diameter drills.

The original Patent (US1523659 of 1919) featuring the compressed air gun for shooting holes in the sides of the sunken ships.

The Tractor

The vehicle itself was described as an ‘endless track tractor’ or ‘mobile tractor’ consisting of a large watertight cylinder mounted on a low pair of tracks. No suspension was provided in the track run on either side which was made from two large wheels, one at each end, separated by 5 smaller wheels. All were attached to a rigid horizontal frame. Drive for the tracks was delivered to the rear-most wheel via a drive chain running from a small motor estimated to be just 20 hp or so mounted inside the steel chamber. Each track was driven independently with the clutch controls worked from a small handwheel. This level of control over the drive to each track was complex but allowed for fine manoeuvering. The operator, who would also have to drive the machine, could maneuver by means of clutches that could engage and disengage with the tracks. Engaging the right track, the machine would move to the left and vice-versa.

On the outside of the chamber was a pressurized hose that could be manipulated by the operator to blast away sand, dirt, and debris from his locale, allowing him to work clearly on the side of the vessel. The chamber itself was divided into two portions. The lower part was attached to the tracked chassis and contained the motor and driveshaft. The upper part of the chamber contained the operator and controls and could rotate, allowing the machine to use its drills against the sides of the ships it was salvaging.

Artist’s impression of the Reno salvage method and underwater tractor at work. Source: The Leader 2014
The raising of the ‘Scally’ as depicted in Popular Science Magazine, September 1923.

Deployment

The tractor unit could not float or ’swim’ and was simply lowered to the sea bed by chains from a hoist where it had limited movement, but it had proven itself to be a viable system. Reno’s underwater salvage firm employed his salvage methods successfully in the 1920s and 30s. It was used in the Baltic for the Estonian government reclaiming parts from the 15,000 ton Russian battleship ‘Slava’ from a depth of 40 feet (~12 m), and closer to home with the recovery of the 500-ton Coast Guard cutter ‘Scally’ which sank off Long Island Sound in 65 feet (~19.8 m) of water. Reno’s suggestion of using this method to raise the Lusitania was not, however, ever taken seriously.

Conclusion

Reno never described his underwater vehicle as a tank. He did have other military ideas but not for this vehicle, although it has appeared subsequently online as some form of underwater tank akin to a Tauchpanzer. The machine was tracked, and potentially armed with a cannon, but it was not a military vehicle. Despite this, the design is an interesting one and important in regards to the development of tracked vehicles as it is likely the first underwater tracked vehicle ever built. It was certainly not to be the last, with both Great Britain and Germany looking at tanks which could drive on the sea-bed in WW2. What became of Reno’s underwater vehicle is not clear, likely it was simply scrapped though, as diving technology caught up through the 20s and 30s. Jesse Reno was inducted into the National Inventors Hall of Fame in 2007 for his work on the escalator and died in 1947, leaving behind a legacy of inventions well known, like his escalator, and obscure, like his underwater tractor.



Illustration of Reno’s Endless Belt Tractor or ‘Underwater Tank’ produced by Andrei Kirushkin, funded by our Patreon campaign.

Specifications

Dimensions (L-W-H) 2.5 x 2.74 x 2.5 meters
Total weight 18 tons (16.3 tonnes).
Crew 1 – 2
Propulsion 20 hp
Speed (road) Maneuvering only
Max. depth 400 feet (~122m)
Armament drill or 4” (101.6mm) gun
Armor Pressure hull

Source

US Patent US1523659 ‘Apparatus for Raising Sunken Ships’. Filed 25th November 1919. Patented 20th January 1925.
US Patent US1523660 ‘Apparatus for Raising Sunken Ships’. Filed 27th December 1919. Patented 20th January 1925
US Patent US136142 ‘Raising Sunken Vessels’. Filed 23rd February 1920. Patented 4th January 1921.
US Patent US1364143 ‘Raising Sunken Vessels’. Filed 2nd April 1920. Patented 4th January 1921.
US Patent US1416754 ‘Device for Raising Sunken Vessels’. Filed 17th March 1921. Patented 23rd May 1922.
US Patent US1400316 ‘Art of Raising Submerged Vessels’. Filed 13th June 1921. Patented 13th December 1921.
US Patent US 1495529 ‘Raising Sunken Ships’. Filed 2nd August 1923. Patented 27th May 1924.
Canadian Patent CA225695 ; Raising Wrecked Vessels’. 7th November 1922
Modern Mechanix January 1935 ‘Under-Sea Tractor-Sphere Roams Ocean Floor’
Modern Mechanix April 1932 ‘Submarine Safety: An Insolvable Problem?
Popular Science Monthly, September 1923
National Inventors Hall of Fame
‘Gunning Wrecks’ Therebreathersite.nl
Grohman, A. (2014). Salvage of the Scally. The Leader.


Categories
Coldwar American Prototypes

LVTP-77 Cybernetically Coupled Amphibian & Articulated LVT

U.S.A. (1966)
Research Vehicle – 1 Built

Ideas about coupling vehicles together and of an articulated body for fighting vehicles are as old as tanks themselves. Coupling two vehicles together offers the designer some significant benefits for mobility and design for a variety of roles, one of which was with amphibian tanks.

Unladen LVTP-5 in the water showing her trim line, later a coupled LVTP-5 was attempted. Source: Dyck and Ehrlich

Amphibian tanks, which can operate on land or in water, have unique challenges to overcome. They have to be buoyant enough to float and yet armored sufficiently to protect the troops and then they still have to deal with the difficult transition from water to land. A coupled or articulated vehicle has the advantage of being long enough to straddle this boundary between water and land and potentially, of being able to cross bigger obstacles than a single-hulled vehicle.

With that in mind, the US Navy started work as early as 1966 studying the effects, benefits, and costs associated with coupling amphibian vehicles together. That study followed work between 1956 and 1958 focusing solely on improving water speeds for amphibian vehicles although due to time and financial constraints it was limited only to wheeled vehicles. Although those tests were inconclusive the one bright light from them was the testing of the ‘Sea-Serpent’ (not to be confused with the amphibian flame-thrower vehicle of the same name). Sea-Serpent was the name given to a multi-vehicle amphibian train of up to eight vehicles coupled together which managed a combined speed double that of one of the single vehicles.

Artwork for the ‘Sea-Serpent’ a series on coupled amphibians and the simple pin connection between the trucks. Source: Nuttall and Kamm.

Building on this finding for such a novel vehicle, in 1966, Davidson Laboratory (DL) looked at the problem from the point of view of tracked amphibians and concluded that it was feasible to couple together up to five LVTP-5s and that this ‘amphibian-train’ had only twice the water friction of a single vehicle. As such, this 5 vehicle train could increase speed by up to 50% in the water alone. Furthermore, the transition zone was traversed more easily by this 5 vehicle train, as were obstacles. Such an increase in mobility constituted a significant military advantage and clearly this success meant there would be further work in this area to expand on this.

The DL experiments did not use actual LVTP-5 but instead accurately shaped and weighed models in a test tank with them connected together by means of simple pin connections at the height of the center-of-gravity (CoG) of the vehicles.

One problem identified during these 1966 tests was that the increased vehicle speed produced an increased sized bow-wave with a consequent increased risk of swamping of the lead vehicle (as there is no bow wave for any of the following vehicles). To counter this, a freeboard shield would be required to be fitted to the lead vehicle of any LVTP-5 train regardless of length (Tests conducted during the 1970’s with coupled M113s also showed this additional freeboard shielding used). Additionally, as a larger freeboard shield was required for any length of LVTP-5 train, it was also found this had the side benefit of itself reducing drag in the water by 5%. In calm water, it required zero freeboard at 7.1 mph (11.4 km/h) and 12 inches (305 mm) at 7.6 mph (12.2 km/h). At 8.3 mph (13.4 km/h) however, she would need 20 inches (508 mm) of freeboard – the same amount as required unladen at 10 mph (16.1 km/h).

Schematics of the 1/12 scale model used for the coupled LVTP5 trials showing the size of the additional freeboard protection required. Source: Dyck and Ehrlich

Spacing

Vehicles used in an amphibian train had to be carefully positioned to reduce drag and the ideal gap between vehicles was found to be 1 foot (300 mm) compared to the original 6 feet (1.8m). This close-coupling reduced drag in the water by 15% and thereafter all testing was done with little or no gap between vehicles. Even with the drag reductions and freeboard changes though, the entire train was still effectively limited to a safe speed of 9.2 mph (14.8 km/h) in the water to provide a margin of safety for rough water.

Additionally for rough water the coupling, DL recommended that it “must be capable of absorbing some degree of shock, if wave or surf operation is contemplated”. They had found that, at a pitch angle of more than 25 degrees, their train broke apart. Obviously, in a real-world situation, this would have proven extremely hazardous.

The 1966 experiments ended with strong recommendations to pursue this modeling to the prototype stage with a train made from real LVTP-5 tested with a view to developing an effective type of coupling and box shields. It is not known, however, if any LVTP-5’s were ever modified in tested in this coupled configuration despite the potential benefits.

M113 CCRV project during snow trials. The vehicle could be controlled from either front or rear vehicle. Source: TACOM/TARDEC

A Project Reborn

The work in 1966 had shown the potential for coupling for amphibians but also highlighted the lack of knowledge in coupled-vehicle systems. As a result, in 1972, money was put aside by Congress for work on cybernetically coupled technologies with positive feedback controls to tray and leverage this coupling technology. The following year (1973), two M113’s were modified and coupled together to form the M226 Cybernetically Coupled Research Vehicle (CCRV). That work showed, once more, great potential. Combined, the two vehicles exhibited greater mobility off-road than an individual vehicle, particularly when it came to obstacle crossing, and used a more controlled system for the coupling compared to the rather crude pin-attachment in the 1966 experiments. This time, instead of an uncontrolled pin vulnerable to excess pitch (in the water) and excess yaw (on land or in the water), the M113 CCRV connector limited movement to a maximum articulation of +/-45 degrees and a yaw of +/-30 degrees.

Control for the system was by means of a simple joystick with positive feedback in all cases, except for pitching where the feedback caused some problems. A simple movement of the driver’s joystick would control the hydraulic arms on top of the vehicle to move the two hulls relative to each other as well as providing stiffness preventing too much pitch and yaw.

The conclusion of the trials in 1974 had proven the experiments in 1966 to be partially correct. A coupled vehicle did exhibit manoeuvrability benefits over the single hull system. Some specific recommendations and findings about the coupled-vehicle system came out of the project including the reduction of water resistance for amphibious vehicles and assisting amphibious assault vehicles in breaching defences.

LVTP-7’s

Irmin Kamm, from the Stevens Institute of Technology and one of the lead authors for TACOM on cybernetically coupled vehicles had already worked on amphibian trains coming up with the Sea-Serpent back in 1969 and then, on the M113 CCRV project. He continued his work on the coupled-vehicle concept with amphibians in 1979 with an evaluation of the concept of a ‘Coupled-LVT’ (LVT – Landing Vehicle Tracked). He was clearly advocating for more work in this area as, in 1979, he concluded that study saying “the advantages [of a coupled vehicle] exceed the drawbacks, it is recommended that existing vehicles be coupled and tested to establish their operational capacity”. The end-user was being clearly identified as the US Marine Corps just like before but the requirements had changed a little. Instead of a coupling permitting +/-45 degrees and a yaw of +/-30 degrees as on the M113 CCRV, this coupled LVTP would have a maximum pitch of just +/- 30 degrees.

Instead of the A-frame drawbar connected to a ball and two hydraulic actuators, this time, the system would be simpler. That older system had to be connected manually but with a new cone-into-cone system, the vehicles could connect or detach on sea or land without having to stop and get out. Each vehicle would simply have a ‘male’ convex cone on the front and a ‘female’ concave cone on the rear, with both located at the center of gravity line. This system was much more versatile. Instead of a master-and-slave unit, as with the M113 CCRV, this time any vehicle so equipped with a coupling cone could connect to any other on sea or land adding a new level of capability to the idea.

Just as before, control over pitch and yaw was performed by either lead or following vehicle by means of a joystick (although a steering wheel was also considered in the study) and the engines would be synchronized to produce the same output. Transmission and braking was to be changed manually though.

With two LVTP-7’s coupled together in this system, the expected performance increases were impressive at a price of additional weight of controls and fittings and a reduction in the internal space in each vehicle. Another note was that the coupled vehicles presented a slightly larger target to enemy fire although from the front the area exposed would obviously be the same. Coupled together, the vehicle would also get a new name. It was to be the LVTP-77.

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Articulated LVT

The name ‘LVTP-77’ appears here for the first time as it is two LVTP-7’s coupled together and rather than sum the two 7’s to make LVTP-14, akin to what was done adding together the ‘113’ part of the two M113’s which were coupled forming the M226, here they simply added a second ‘7’ to make LVTP-77. Looking at the figures for the LVTP-77, they clearly demonstrate that the coupled amphibian is more stable and faster in water, and in fact, faster on land too, with better obstacle crossing, but there was one other concept investigated by Kamm as an alternative. This was an articulated vehicle made from multiple-units comprising a single vehicle rather than two or more vehicles combining.

This articulated vehicle would have two sections of 14 feet (4.27m) and 19 feet (5.80 m) respectively fore and aft with a single 890 gross horsepower engine and weighing 54,000lbs (24.5 tonnes). The fore-section contained the engine and transmission and the rear section contained all of the crew, and an auxiliary engine.

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The 1979 study had concluded that a coupled amphibian was not only possible and beneficial but also desirable, as was an articulated LVT. The recommendation going forwards was to design, install and test a suitable coupling on either a pair of LVTP-7’s or LVTPX-12 vehicles.

Coupling the LVTP’s

With the M226 CCRV, it was simple. It was just a test rig so it did not really matter if the combat capabilities, such as the troop space, were severely hampered. For the actual project with LVTP-7’s or others, the rear ramp and emergency exits had to be kept clear, as would the cargo hatch. Unlike the M226 CCRV, the coupling had to be remotely connectable and disconnectable on land or water and each vehicle had to be able to operate as either the master or the slave. For an articulated LVT, the vehicle was to be limited to 33’ (10.06 m) and had to be equipped with a rear exit ramp and top cargo hatch. The restriction of just one driver was not a problem, but the articulated vehicle was also supposed to be able to dump one part of itself and be able to operate independently on land if needs be. Hence, the reason for the auxiliary engine in the aft unit of the articulated LVT design.

There were 12 separate coupling systems suggested for the coupled LVTP, but only a single viable design for the articulated LVT. The types of connections considered were ball joint, off-center ball joint, symmetrical yaw, symmetrical yaw with independent pitch control, dependent pitch and yaw, dependent pitch and yaw with coupling frame, yaw – no roll, pitch only, turntable, trunnion mount, trunnion mount- internal coupler, and, split pitch and yaw. Only the split pitch and yaw type was suitable for both remote coupling and further development.

The articulated LVT was perhaps more promising as it did not need to concern itself with the problems of remote coupling. In keeping with articulated and coupled vehicles though, the turning radius was large, 35’ (10.7 m), over twice as big as a single LVTP-7 but substantially less than either the coupled M113CCRV or the LVTP-77.

All of the pitch and yaw controls were completely contained within the vehicle with steering by the simple means of yaw control from the driver. The front unit’s 850 ghp engine would be supplemented by a 100 hp auxiliary engine in the back providing some very limited mobility in the absence of the lead unit or if it became damaged by enemy fire. In the normal situation though, this 100 hp engine was used only for driving the pumps for moving the actuators for the coupling.

Power in the water was to be provided by water jets enclosed in the fore sections powered from the main engine. Although it would be more efficient in water-drive terms to have them in the rear section, it was a more efficient use of weight and space to have them in the front. Steering in the water was by means of water deflectors in the jets which moved in conjunction with the yaw of the vehicle for efficient steering. The articulated vehicle would only need one driver who was required to be in the rear although was ideally to be in the front section for visibility. The coupled vehicle concept, on the other hand, would require a driver in both sections to ensure smooth operation and obviously would not need to couple up remotely. In an emergency, it could decouple from the front unit by means of an explosive bolt – in this was the driver did not have to get out at all.

Having conducted various analytical work on the concepts for arrangements of the LVTP-7 and LVTPX-12 models, trials were carried out and once more confirmed the efficiency of coupling an amphibian. Unlike the coupled LVTP-5, which does not appear to have gone further than the concept stage, there was work carried out between 1979 and 1980 on the LVTP-7 project.

The Articulated LVT

The other part of the project which seems to have gained no traction was the Articulated LVT. Despite being better in many regards than the M226 and LVTP-77, simpler, no remote coupling or uncoupling, a single driver, etc., the project simply did not get anywhere yet was a fairly straightforward design. Two sections, engine at the front with the crew at the back, it could pitch through +/- 30 degrees and yaw to +/-34 degrees. Two small turrets on the aft portion contained cupolas for the commander and driver with the secondary weapon (unspecified but likely a .50 caliber machine-gun) in the commander’s turret. The troop compartment behind this was large with enough space for 6-8 Marines provided with a large rear ramp. The front section allowed the vehicle to climb obstacles the LVTP-7 could not and propel it through the water just as well as the LVTP too. An added advantage was that this fore-section would also be the first part coming out of the water to draw enemy fire but, being completely unmanned, did not matter. Instead, it actually served to provide substantial protection for the aft section and in the event of the fore section being damaged the auxiliary engine could simply move the vehicle forward and use the fore section as a large shield until it could be discarded. No armor is actually specified anywhere in the design, but it is a reasonable assumption to assign values comparable to the LVTP-7.

Drawings of the proposed Articulated LVT. Source: Kamm and Nazalwicz

Floating in the water, the fore section with the water jets tilted upwards sharply directing the water jets down whilst the main vehicle was relatively level behind it. Poking out just above the water from this fore section was another weapon, remotely operated and forming the primary weapon for the design specified only as an ‘automatic weapon’.

Drawings of the proposed Articulated LVT. Source: Kamm and Nazalwicz

Putting the LVTP-77 Concept Into Reality

Tests took place at the USMC camp, Camp Lejeune, North Carolina in 1979 and 1980 with LVTP-7 being tested firstly with three new designs of bow planes to cope with the anticipated larger bow wave. These new bow planes were 54” (1,372 mm) long, 42” (1067 mm) long, and 42” (1,067 mm) with a 6” (152.4 mm) lip. The vehicles were tested for speed at Courthouse Bay and at the Battalion Maintenance Pier followed by open water tests in the open ocean off Onslow Beach, all at Camp Lejeune, compared to an unmodified vehicle and a ‘jury-rigged’ coupling between two LVTP-7s.

Arrangements of the experimental bow planes tested on LVTP7s at Camp Lejeune 1979-1980. Source: Kamm and Nazalwicz

The results showed that the increased bow planes did not directly affect speed by reducing drag, but did reduce swamping which allowed for a small increase in speed. Regardless, however, the coupled LVTP-77 was faster by about 0.5 mph (0.8 km/h) in all conditions even without a bow plane and the method of coupling was inadequate with the vehicles too far (about 24 inches / 610 mm) apart, something known to increase drag. Had the coupling been properly constructed and fitted no doubt further improvement could have been made.

Experimental coupling tested at Camp Lejeune for two LVTP7’s. Source: Kamm and Nazalwicz
Very poor quality image showing the two LVTP-7’s coupled together during open water testing. Source: Kamm and Nazalwicz

The tests concluded that a new bow plane should be designed and made for the LVTP-7A1 to reduce the swamping experienced at even 6.5mph in calm waters and further work should be done on the coupled LVTP idea. The gap between the vehicles was going to be a problem though, the requirement for the ramp to still lower guaranteed the vehicles had to be too far apart to make complete use of the extra efficiency when in the water.

Either way, the coupled LVTP7 idea was dropped. The benefits were obvious, but simply did not outweigh some of the associated problems and the money to develop the system was not available. As a result, the whole project was terminated. It is assumed that the two LVTP-7’s modified with the coupling were simply returned to USMC service straight after the trials. The articulated LVT was even less successful. Despite being the logical solution to the coupling development, it never got past the proposal stage. The LVTP-7 was serviceable and available and budgets, seemingly, were better spent elsewhere rather than on a relatively small improvement to an existing vehicle.



Illustration of the LVTP-77 Cybernetically Coupled Amphibian produced by Tank Encyclopedia’s own David Bocquelet

Specifications (LVTP-77)

Total weight, battle ready 103,968lbs (47.2 tonnes) to 106,500lbs (48.3 tonnes)
Crew Minimum 1 (driver), ideally 2 (one in each vehicle)

Specifications (Articulated LVT)

Dimensions 33 ft x 14 ft x 19 ft (10.06m x 4.27 x 5.79 meters)
Total weight, battle ready 54,000lbs (24.5 tonnes) fore section 15,200lbs (6.9 tonnes), and aft section 38,800lbs (17.6 tonnes)
Crew Minimum 1 (driver)
Propulsion main engine LCR-V903 890hp, auxiliary engine 100hp
Armament primary automatic weapon in fore section controlled remotely, secondary weapon on commander’s turret on aft section

Sources

Cybernetically Coupled Research Vehicle. (1974). Ronald Beck and Irmin Kamm, Stevens Institute of Technology, USA
50 years of the International Society for Terrain-Vehicle Systems: Ground Vehicle Mobility, Modeling and Simulation ar TACOM-TARDEC ‘A Brief History’ (2012). Dr. Peter Kiss and Dr. Sally Shoop Editors. International Society for Terrain-Vehicle Systems, Germany
The Water Performance of Single and Coupled LVTP7’s, with and without bow plane extensions. (1980). Irmin Kamm and Jan Nazalwicz. Ship Research and Development Center, Office of Naval Research, Department of the Navy.
Drag Studies of Coupled Amphibians. (1966). R.L. Van Dyck and I. R. Ehrlich. Office of Naval Research, Department of the Navy.
Department of Defense Appropriations for Fiscal Year 1973. (1973). United States Congress Appropriations Committee
Analysis of Obstacle Negotiation by Articulated Tracked Vehicles: The State of the Art. (1981). Peter Brady. Naval ship Research and Development Center, Office of Naval Research
High Speed Wheeled Amphibian: A Concept Study. (1969). C. J. Nuttall and Irmin Kamm. Davidson Laboratory, Stevens Institute of Technology, USA
An Evaluation of the Coupled LVT Concept. (1979). Irmin Kamm, Peter Brown, and Peter Brady. David Taylor Naval Ship Research and Development Center, Stevens Institute of Technology, USA


Categories
WW2 Australian Prototypes

Wales – Whitehead Amphibian Tank

Australia Australia (1941)
Amphibious Tank – None Built

In March 1941, Messrs. Wales and Whitehead wrote to the Australian Army Inventions directorate with a memorandum and booklet proposing the construction of an amphibian tank along with an armoring system designed to overcome the problems which existed in Australia at the time with the manufacture of heavy armor plate. An amphibian tank would suit much of the terrain in which Australian forces were fighting in the Far East. The terrain was often swampy or involved transport on and off islands, terrain unsuited to conventional tank designs.

The design

The proposal did include two drawings. One of the proposed vehicle, and a second for the proposed armor plate, but sadly only the armor sketch survives, so it is hard to know exactly what this vehicle might have looked like. The proposal itself was very brief, just a two-page letter, but it was a well thought out and considered proposal, perhaps more than some of the inventions and ideas sent into the directorate during the war.

The overall shape of the vehicle is not known, but it was envisioned to be 18’ x 9’ x 8’6” (5.48m x 2.74m x 2.59m), and to use equalized spring suspension when traveling on land, which was seen as being particularly useful when traversing undulating ground. Displacement in water was stated to be 430 cubic feet (12.17 m3) for a vehicle measuring 18’ x 9’ x 8’6” (5.48m x 2.74m x 2.59m). This 12-ton vehicle was driven and steered by means of a controlled differential from an unspecified pair of V8 or similar engines. The main shafts for this design were positioned under the working floor level of the tank.

For protection this design was to use “2” (50.8 mm) thick armour plate equalling 80 lbs/sq.ft., but using a composite scheme consisting of armour plate and wood rather than simple steel armour plate. The metal layer of the armour was to be formed from rolled sheet and this laminated scheme was seen to provide ample protection and the potential to be reduced to 40 lbs/sq.ft. in the future. Several overlapping layers were used.

Assessment

All invention suggestions submitted during the war were subjected to a technical assessment by a committee of experts, and the Wales/Whitehead Amphibian, being a very thoroughly drafted idea, received an equally thorough appraisal. In terms of vehicle weight, the 12 tons envisaged by the designers was seen as unrealistic when considering the proposed size of the machine with 2” (50.8 mm) of armor plate. The assessment considered that armor at 40 lbs. per square foot (195 kg / m2) was possible for the desired 12 tons weight of the vehicle, but that this would be barely bulletproof. A little confusingly though, under ‘Armour’, the evaluation contends that in terms of the scheme for 2” of armor that:

I have no reason to suppose that the proposed armour is, in any way superior to a single homogenous plate…. It is not clear how the various laminations are bonded together

This, then, means that the 2” of armor in the design was not just a single homogenous layer of armour but some type of laminated protection possibly accounting for the thickness and the relative light weight of the machine. The design had mentioned the use of wood, but the exact composition is not known.

Whitehead and Wales’ laminate armour design showing the multiple layers of steel and wood bolted together they planned to use in their tank design. This design was not adopted. Image Source: Author

Floating

In terms of floatation, the technical assessment looked at the design seeing it would displace less than half of the stated 430 cubic feet (12.17 m3) and were not able to figure out how the designers came up with 430 cubic feet. It was assumed that in order to do so, the track guards were to act as floats for the machine. This design was condemned as it was open at the bottom, allowing any trapped air to escape easily adversely affecting buoyancy. Either way, the floats would be easily pierced by enemy machine-gun fire. The designers had selected a pneumatic gun mounting to resist the gun recoil of “as large a calibre gun as possible”, but did not specify a particular weapon. The only weapons specified were the machine-guns which were to be Bren and Lewis guns positioned on the vehicle in locations to be determined by the military.

The inventors were vague as to exactly how the machine could enter the water at ‘launch’, suggesting some kind of lowering would be needed, but this obviously rendered the machine unsuitable as an easily launched amphibian.

Firepower

For armament there was a complete disagreement between the inventors and the military experts. The inventors contended that it was the recoil length of the main gun which limited the firepower available whereas the experts concluded that this was not a problem and that the stowage of ammunition was a far bigger factor in determining the gun carried.

Termination

Following this assessment, the Army decided it was not worth further consideration, although the technical appraisal section of the department did have a few points of its own to raise which did not agree with those of the Army experts.

The technical appraisal section did not, for example, agree with the overall characteristics of the design, saying it was done to provoke some discussion so that it could be developed further for submission to the inventions board. Further, the low weight of the machine (just 12 tons) was as a result of the 40 lbs/sq.in. protection rather than the original 80 lbs./sq.in. and that the final weight would depend entirely upon the armor protection specified by the military – an entirely fair point.

Having made that fair point about the protection and weight, the section in the proposal did not accept the criticism of the scheme stating that “the writer [of the assessment] has no direct evidence of the efficiency of the proposed armouring” and that simple tests should be done to check out their idea. Here, this section also made clear that the proposed armouring scheme may have used more than just a lamination of steel or steel and wood. The appraisal of the design specifically referred to the armour on some British Cruiser tanks in the desert whose protection consisted of two armour plates with an airspace between them which suggests the armouring scheme involved some novel ideas about spacing between plates.

For floatation, again, the criticism was rejected, saying that the track guards did not play any part in floating the machine and the “the criticism does not apply being misconceived”

End

The Wales/Whitehead Amphibian Tank was considered to be well thought out and used some novel features. It had gained sufficient interest for the Army to consideration and the technical assessment did, in some regards, rate the vehicle as worthy perhaps of some further investigation.

The Army though was not interested, and was dismissive of the whole concept. Their final word on the matter was that it did not justify expenditure to investigate and that “in any case, there is no requirement, from the General Staff, for an amphibious tank”.

The Wales/Whitehead design then, regardless of what merits it may have had, was terminated and the drawings of the tank were sadly lost. All that remains of it are a few pages in a file. It is not even known who the two designers were as there is no information remaining to identify them.

Wales/Whitehead Amphibian Tank specifications

Dimensions 18’ x 9’ x 8’6” (5.48m x 2.74m x 2.59m)
Total weight 12 tons
Propulsion pair of V8 or similar engines – controlled differential drive
Suspension Equalised spring
Armor 2” (50.8 mm) thick laminate steel/wood

Sources

Australian Inventions Directorate File G177/701/1264 March – April 1941

Categories
Coldwar American Prototypes

Ridlon’s Main Battle Tank

U.S.A. (1962-1963)
Main Battle Tank – None built

By 1962, the 105 mm Gun Tank M60 was still a new tank in service with the US Army but, just like any current system, was already being considered for future replacement, redevelopment, and upgrading. The latest generation of Soviet tanks were well armed and armored, and much smaller than their American counterparts. A new tank would be needed to deal with this increasingly dangerous threat. During the height of the Cold War in 1962, the Armor Association of the United States Army held an open competition for the design of a new tank. Of the designs submitted, some were clearly better thought-out and practical in terms of production, cost, and combat effectiveness than others.

Nonetheless, the competition formed part of one means by which the US Army could assess new and novel ideas for the potential next generation of tanks. One such tank, perhaps the most outlandish of the top four finishers, came from the fertile mind of Everett Philip Ridlon of Hibbing, Minnesota. Ridlon, an electrical engineer by trade. He submitted a quad-track tank with a crewless turret propelled by a hybrid-drive system based on the M60.

Everett Ridlon 26/7/1934 – 9/7/2011. The designer of the tank. Source: Armor Magazine

Suspension

Probably the most obvious thing about Ridlon’s design is the suspension. Six wheels on each side divided into groups of three with a strong angling at the front and back respectively. Assuming the raised wheel at the front of the lead unit and rear of the rear-most unit were the drive sprockets this provided a strong degree of redundancy in the design so that should one unit become damaged by enemy fire or a land mine or accident, the vehicle would not be immobilised. Each wheel was held on a single arm providing a good degree of movement and is reminiscent of the suspension arms of the M60. If it was just like those on the M60, then the arms would be hydraulically damped in their movement.

Viewed from the front of the tank the curved lower hull of the M60 is clearly similar in style to that envisaged by Ridlon and shows how these suspension arm units would have to project from a curved body. Also visible at the back in the angled hydraulic damper and also the track tension adjuster to the idler wheel at the front. Source: Author

Hull

The design of this vehicle was not going to need a new tank hull, as Ridlon simply planned to reuse the lower hulls from the M60. He proposed stripping out of the original drive components and fitting a new engine and the motors. On each side in the middle, where the two track units were closest to each other, the road wheels would be on the ground, creating a large empty space above them. This meant that the new upper hull of the M60 donor tank was going to need to bulge out across the side to improve the ballistic protection in that area.

Within the hull would sit the two crew along with the myriad of engines and motors proposed. In amongst all of this would be compartmentalised storage for fuel, compressed air, hydraulic fluid, water, fire extinguishers, and other items which were seen as being able to add to the protective structures around the crew.

Ridlon’s crude and un-detailed sketch of a future main battle tank. Source: Armor Magazine

Armor

The lower hull would be that of an M60, but the upper half would be remade to feature a large curved section across the top half bulging out at the sides to make use of the low section above the ends of both track units on each side. Further, Ridlon wanted the armor to be made in sections so that, as it was hit by enemy shells, the outer sections would break away on impact. To accomplish this, he wanted the outer sections of the armor to be made ‘soft’, with ‘hard’ armor on the inside, in what he describes as a “live” system. Further, he stated “the outer armor is composed of ribbed interlocking plates which give greater depth of armor and less weight as well as catch the projectile higher on the sides and thus disperse impact energy over a larger surface area”. The whole plan was not practical in that sense, but it could be considered as modular as each damaged section could at least be replaced.

Firepower

The drawing of the turret and main armament is almost comically poor, with an impossibly small turret described as a ball-type turret. In this turret were to be two machine guns and either an automatic cannon or an automated one. The turret, as drawn, certainly appears far too small to accommodate any men but, if it is considered to be a remote turret, and a ball-type turret at that, it seems a little less ridiculous. Those turret-mounted weapons were not the end of the arsenal the tank would carry, as Ridlon also proposed rocket tubes should be placed in the upper hull, capable of attacking ground or airborne targets.

Automotive

Ridlon, somewhat preciently for a US Main Battle Tank, proposed the use of a very small ‘gas turbine’, that is, a turbine-type engine running on petrol. This engine was not to directly drive the tank though, but was to drive a series of small high-speed homopolar generators. Each of these generators would be spread around the vehicle to minimize the chance of a single one becoming damaged and incapacitating the vehicle. Ridlon envisaged this system being duplicated for all military vehicles, as the humble Jeep would need just a pair of these small generators, a truck three and eight for a tank. Ridlon proposed eight small turbines working together to deliver power to thirty-two motors which powered the four sprockets which drove the tracks. The idea was that, by increasing the number of possible drive options, it would be impossible to be crippled by the loss of any one drive unit, motor or generator. The chances of all of those elements being made to work without something breaking seems highly optimistic even though it is the best part of his design considering elements of protective redundancy in the drive units to avoid being crippled and vulnerable to enemy fire. Rearranging the automotive elements of the tank to multiple small motors and generators would have made significant changes to the internal layout possible but that was beyond Ridlon’s skills as a designer, which perhaps explains why the drawing was so poor and the ideas on armor so poorly conceived.

Conclusion

Ridlon’s design took third place in the Armor Association’s competition, behind the Forsyth brothers’ coupled-tank and Eischen’s MBT, yet is drawn and described very crudely. The design appears utterly impractical with multiple complex systems, yet was held in high regard by the Armor judges. The question is why?

Perhaps it was a combination of novelties of the ball unmanned ball turret, the hybrid drive, the compartmentalisation or some or all of those, but whereas the Forsyth design was a competent and well thought-through design, this vehicle was simply impractical and an example of fantastical thinking for the time. There was no likelihood this vehicle would ever have been built and its inclusion in third place seems surprising given other better thought out designs. Ridlon did better than his tank design did, by 1970 he was teaching at a technical college before retiring in 1992. He died of lung cancer in 2011.



Illustration of Ridlon’s Main Battle Tank, based on his original sketch, produced by Andrei Kirushkin, funded by our Patreon campaign.

 

Specifications

Crew 2
Propulsion Petrol-Electric (8 Petrol turbine driving 32 high speed homopolar generators)
Armament 2 machine guns, cannon, surface to air/ground missiles

Sources

Armor Magazine January-February 1963
Hibbing Daily Tribune, 12th June 2011 ‘Everett Philip ‘Babe’ Ridlon


Categories
Coldwar American Prototypes

Composite M2 Bradley IFV

U.S.A. (1983-92)
Infantry Fighting Vehicle – 1 Turret & Hull Built

The pressure on armored vehicle designers to keep down weight without compromising protection or performance is great. Much focus has been made on moving away from traditional steel armor to aluminium or even titanium and ceramics as an alternative. Whilst these can improve weight without reducing protection, they come with an often very steep price tag as well as other problems. One idea from the early 1980s was the possibility of using a new generation of fiber-reinforced plastics to form the hull of armored fighting vehicles, which led to the creation of a composite body M113 Armoured Personnel Carrier (APC). Whilst the M113 was already obsolete and being replaced with the M2 Bradley Infantry Fighting Vehicle (BIFV), the glass fiber composite technology had shown the potential of not just reducing weight of the new APC but also of increasing protection at the same time. The composite used on the M113 was rather basic and would be improved with the first generation of integrated ceramics to provide improved ballistic protection.

Composite-hulled M2 Bradley Infantry Fighting Vehicle with non-composite turret. Source: Pilato and Michno

At the same time, Food Machinery Corporation (FMC) of San Jose, California, the parent firm for the M113, undertook the development of a composite turret for the Bradley with the project starting in 1983, manufacturing 5 turrets by the middle of 1987. Unlike the ‘double sandwich’ of the hull used on the M113, this turret composite was a single layer of polyester bonded S-glass. Overall, the turret was identical in shape and layout to the standard M2 Bradley turret except that it was made in two halves with the resin impregnated glass fiber cloth and then joined together with a metal frame. Making the turret out of S-2 glass fiber/polyester resin composite saved 15% over the weight of the original turret structure with similar levels of ballistic protection. This turret design was then sent for firing trials at Camp Roberts, California, in Autumn 1986. These appear to have been successful, as, by September that year, FMC was awarded a further contract from the US Army Materials Technology Laboratory (M.T.L.), Watertown, Massachusettes to develop this idea further with a composite hull for the entire vehicle.

This hull is referred to technically as Glass Reinforced Polyester (GRP) hull, but often shortened simply to ‘plastic’. The structure of this vehicle was essentially the same as that of the composite turret, consisting of just a polyester bonded S-2 glass fibre, and fabricated in two halves (with the floor panel as a single piece rather than having a seam) which were then joined together using an aluminium alloy frame. Unlike the early tests of the composite M113, this was simpler to produce, lacking the ‘sandwiching’ of the earlier trials. Metal was not eliminated completely either from the prototype, as the turret ring remained metal, as did many of the fittings and the whole rear ramp arrangement. The aluminium frame providing the stiffness for the hull and to which the halves were attached also served as the attachment point for the suspension arms. The hull construction consisted of a floor deck and two side panels, each 2.4m x 6.7m fabricated from plies of S-2 glass fibre in polyester resin ranging from 22 to 69 plies thick. After fabrication and post-manufacture finishing, each panel weighed just 820 kg, a saving of 25% over the original metal structural panels. Work on the composite turret would be less successful and indicate that switching out just the aluminium-armour parts for composites could result in a weight saving of 15.5%.

The fabricated hull showing the composite construction. Source: Army Research Development and Acquisition Bulletin, 1990

Unlike the marginal improvements with the M113 composite hull, the weight saving for the Bradley composite was large, 27% lighter than the standard hull, even with the additional ceramic exterior tiles as applique armor.

Just like the turret, the hull was tested ballistically too. In terms of protection, it was more resistant against explosive blasts and more resistant to spalling than the standard M2 Bradley. The tests had been successful and significant savings in weight could be made, although the cost of mass production of such hulls, not to mention longevity issues, were still to be addressed. One additional advantage of the plastic hulled vehicle was that it had better thermal properties than the metal hull. It stayed cooler and was less prone to overheating, providing better insulation. On paper at least, it was successful enough that in 1992 a new project was started known as the Composite Armored Vehicle (CAV), intended to develop the technologies needed to produce a range of composite hulled military vehicles. That project was developed by United Defence as the third generation of their program of ceramic composite armor development with the Bradley constituting generation 1 and the M8 AGS, generation 2.

Protection

With the majority of the aluminium hull replaced with the S-2 glass fibre composite, the vehicle had structure but lacked the ballistic protection required to protect against the Russian 14.5 mm round. As a result, the vehicle was designed to take special ceramic tiles bolted to the outside. These tiles were made from TiB2 (titanium diboride), an extremely hard material (1800 Knoop, a hardness test unit for very thin or brittle materials) with a high melting point (2970 Celsius) and high density (4.52 g/cm3). Compared to steel with a density of 7.85g/cm3 and aluminium 5083 armor with a density of just 2.66g/cm3, TiB2 lay half way between the two materials but was more than ten times harder than aluminium (1800 Knoop vs 109 Knoop). These rectangular tiles were overlaid with each other in a ‘brick’ weave pattern.

Tile pattern on side of the BIFV. Source: McCauley et al
Composite-hulled M2 Bradley Infantry Fighting Vehicle with non-composite turret. Source: Richard Eshleman

Problems

Ignoring issues with the weight, there was a more fundamental problem with the composite body for the M2 Bradley. Just as was found during the same tests with the composite body for the M113, the new plastic hulls exhibited significant longitudinal twisting during testing. In comparative testing though, the small M113 came out better than the larger M2 Bradley in this regard. When fitted with engine, hatches and equipment etc., it simply showed less twisting along the longitudinal axis. Both designs showed themselves equally good at absorbing vibrations, with the plastic hull better than the metal versions.

Rear view of the testbed vehicle circa 1989. Source: Army Research Development and Acquisition Bulletin, 1990

The completed FMC Composite M2 Bradley Infantry Fighting Vehicle (BIFV) was shown off to 200 assorted military, media, and FMC representatives in June 1989 when it was unveiled by General Louis Wagner, then head of the US Army’s Materiel Command. From this public unveiling, it was taken to Camp Roberts in California for 6,000 miles (9,656 km) testing under real-world conditions. Optimistically at the time, the composite BIFV was seen as being able to deliver a 25% weight saving along with improvements to vibration, noise reduction (10dB), reducing spall, lower radar signature, improved thermal efficiency, improved protection against mines and a 20% saving in the cost of manufacture along with lower life-cycle costs. Certainly, these were very exciting potential benefits and they were, overall, somewhat successful. The composite M2 BIFV never went into production though, the hull could still be improved, the external ceramic tiles were too vulnerable to damage and, as with all composites, the issues of repair and multi-shot resistance were not addressed. Instead, a new project was started in 1992 – the Composite Armored Vehicle (CAV) program. This would require the manufacture of a completely new vehicle as a demonstrator test-bed for composite armors known as the Advanced Technology Demonstrator (ATD) as part of the US Army’s Thrust program. More than one company submitted bids for a new composite hulled vehicle platform for the US Military but the program faded out. The work on proving the technology on the M113 and then on the M2 Bradley was to evolve and find use in the CAV-ATD program, but the Composite M2 was not adopted. The fate of the prototype M2 Composite hull is not known.

Unveiling and examination of the composite hulled Bradley at AUSA. Source: Richard Eshleman’


Illustration of the Composite M2 Bradley modified by Pavel Alexe based on work by David Bocquelet, funded by our Patreon campaign.

Sources

Bradley: A history of American fighting and support vehicles. (1999) R.P. Hunnicutt, Presidio Press
Modal Analysis of the M113 Armored Personnel Carrier Metallic Hull and Composite Hull. (1995). Morris Berman. Army Research Laboratory
Aluminium 5083. (2018). ASM Aerospace Specification Metals Inc.
Ceramic Armor Materials by Design. (2012). James McCauley, Andrew Crowson, William Gooch, A. Rajendran, Stephen Bless, Kathryn Logan, Michael Normandia, Steven Wax. Ceramic Transactions Series No.134
Fourteenth International Conference Proceedings. (1999). American Society of Composites.
Composite Fighting Vehicle ‘Rolled Out’. (1989). Carrick Leavitt. UPI
Army Research, Development and Acquisition Bulletin, January-February 1990
Advanced Composite Materials. (1994). Louis Pilato, Michael Michno, Springer-Verlag, Berlin


Categories
WW2 German prototypes

Schwerer-Flammpanzer auf Tiger I (Flammanlage auf Tiger I – ‘Flammpanzer VI’’)

Nazi Germany (1944-45)
Flamethrower Tank – Experimental Only

There is something about a flamethrower that induces the primordial fear amongst those on the receiving end. The awe of seeing a sheet of flame projected towards you with little or no chance of stopping it was recognized as a very effective psychological weapon during World War I, when these devices first started to be fielded. Even as far back as then, there were ideas and plans to mount these flamethrowers into tanks. An armored all-terrain platform makes a lot of sense for a flamethrower-carrier, as it is protected by its armor from the small arms of the enemy but also able to traverse the rough or broken ground in front of the position. Further, whilst a man-portable system was limited by the ability and stamina of the man hauling it, a vehicle was not. A vehicle-mounted flamethrower system could carry far more fuel for a bigger flame thrower with a longer range than was possible with a man-portable system.

The Germans, right from World War I, were fans of flamethrowers and understood the potential of them both in their direct military application for clearing an enemy position as well as for their psychological effect. Various German tanks in World War II were trialed with flamethrowers, although some are better known than others. One of these projects that is mostly forgotten and was never realized in a vehicle was the fitting of a heavy flamethrower into the hull of a Tiger I, the Schwerer-Flammpanzer auf Tiger I.

Flamethrowers mounted on the Panzer I (Pz.Kpfw.I Ausf. A), also known as ‘Flammpanzer I’, were used in North Africa against the British and a version known as the ‘Flamingo’, based on the Panzer II (Pz.Kpfw.II(F) Sd.Kfz.122), also known as ’Flammpanzer II’, was used on the Russian Front. Both of these vehicles saw relatively limited service. They were simply too vulnerable to enemy fire with thin armor which even an anti-tank rifle could penetrate from the front. As such, the poor range of the flame projectors they mounted left them very vulnerable to being penetrated as they had to get too close. This, and carrying hundreds of liters of fuel inside the tank was thus a recipe for disaster for the crews. The Flammpanzer I had mounted its projector in the turret alongside a single machine gun but the Flammpanzer II went for two nozzles, one on each front mudguard over the tracks (Spritzkopfe – Spray Heads). Each was independently operable, able to be rotated through 180 degrees. The turret was changed to include new vision ports permitting a better view of each nozzle as it worked and just a single machine gun. Flame time for the Flammpanzer II was limited. Just 160 litres of fuel were carried, enough for up to 80 ‘shots’ lasting up to 2-3 seconds each with the usual method being to douse the target with fuel before igniting it.

Flammpanzers I and II (Flamingo) showing the turret-mounted flame-projector on the Panzer I and the front-wing mounted projectors on the Panzer II. Source: Jentz et al. (left)

A solution to the lack of armor on the Flammpanzer I and II was to use the hull of a more heavily armored tank. Whilst it was on a much slower platform, a successful flamethrower was retrofitted to captured French Renault Char B tanks (Pz.Kpfw.B2 (F1)). Powered by a J-10 Motor driving a pump rather than being reliant upon cylinders of compressed nitrogen gas as the propellant like on the Flammpanzer II, this system had a range of 40 to 45 metres with enough fuel for about 200 separate bursts. This was a new type of fitting designed by Wegmann, although the actual flamethrower was designed by Koebe. This partnership paired the heavily protected Char B hull with the flamethrower, allowing, at least in theory, for the vehicle to get close enough to the enemy to make use of it.

Two views of the front-mounted flame-projector fitted to the front of the captured French Char B2 (Pz.Kpfw.B2 (F)). Source: Jentz et al. via The Tank Museum, England

The Panzer III (Pz.Kpfw.III (F) Sd.Kfz.141/3) flamethrower version, also known as the Flammpanzer III, was different to the Pz.Kpfw.B2 (F) using a Koebe* HL II 40/40 1000/20 pump which, in turn, was driven by a two-stroke 28 hp Auto Union ZW 1101 (DKW) (1,100 cc) engine. It could achieve a jet of burning flame oil out to just 60 metres at a pressure of 1.52 to 1.72 MPa (15 to 17 atmospheres) and a rate of 7.8 litres per second. The fuel mix itself was a mixture of oil and petrol to create a thickened burning fluid which was easily ignited by means of Smits glow plugs (Smitskerzen). This system had far better mobility than the Pz.Kpfw.B2 (F) retrofitted system, but still required improvement and found limited use.

*(Koebe was the firm of Hermann Koebe Feuerwehr-Geraete-Fabrik of Berlin, a manufacturer of fire-fighting equipment)

Panzer III (Pz.Kpfw.III (F) Sd.Kfz.141/3) ‘Flammpanzer III’ in action. Source: Jentz and Doyle
Koebe HL II 40/40 1000/200 auxilliary pump and fuel tank (on top) as used in the Pz.Kpfw.III (F) to deliver the flame-fuel. source: Jentz et al.

Enter the Tiger

Despite the successful use of various flamethrower-armed vehicles, including tanks and half tracks, during the war, it was clear to the Germans that the short range of the flame systems used meant that the vehicles carrying them had to get too close to the enemy and this rendered them vulnerable to fire. The solution was twofold: first, put the flamethrower on a heavily armored platform (like had been tried on the Pz.Kpfw.B2 (F)), and secondly, partner this with a new, longer-range flamethrower system.

At the end of 1944, a solution was proffered by Hitler. On 5th December 1944, during a conference, he requested that a long-range flamethrower should be mounted behind as heavy an armored chassis as possible. Various heavy tank projects had been suggested up to and including the Maus (which had been through its own flamethrower development by this time). The Tiger II chassis was the most well armored vehicle in service which was in production at the time, but chassis for that vehicle were at a premium. The next best thing of course was the Tiger I (Sd.Kfz.181 – Tiger Ausf. E), a vehicle which had finished production and for which there were hulls available as vehicles were brought back from the front for repair.

Repurposing these hulls for this use was not dissimilar from the idea to reuse hulls for the Sturmtiger programme, as it meant that a tank which might have had severe and irreparable turret damage could be reused for the war effort. Unlike the Sturmtiger though, this flamethrower idea would not require extensive rebuilding with a new superstructure and weapon system. Instead, the plan was much simpler. Hitler’s goal was a Flammpanzer with frontal armor which was impenetrable to enemy fire with a target of 250 mm, but the Tiger I, with armor up to 120 mm thick on the front, would have to do in the short-term. This demand was repeated by Hitler on 29th December 1944 and the task passed over to Obert Crohn of the Entwicklungskommission Panzer (Tank Development Committee).

Preserved Tiger 131 at The Tank Museum Bovington. Currently the only running Tiger tank in the world. Source: Mark Nash

Development

Reusing Tiger I hulls would mean there would be no need to design a chassis on which to mount this flamethrower but there were still technical hurdles to overcome. First was the flame-part of the problem and, on 23rd January, Obert Crohn reported a solution. It was a reversion to the older high-pressure gas-based delivery system but it would provide a significantly longer range flamethrower, at 120-140 metres. The mounting for the weapon was selected as being the machine gun port on the front of the Tiger, meaning it could be directed by the man in the front right who had previously had the role of radio operator/hull machine gunner, but there was still the issue of the fuel tanks. The interior of the Tiger was crammed full already with the equipment it needed to function as a tank as well as the turret basket, ammunition etc., so there were only two easy options for the fuel. Either it would have to be hauled in a trailer behind (a solution adopted famously by the Churchill Crocodile) or else the turret would have to be removed to create the space. The advantage of a trailer idea is that the main gun could be retained, but this would come at a cost. The trailer would be vulnerable and, since the surplus Tiger Is were those with damaged turrets anyway, the turretless internal-fuel-stowage option was chosen instead. This would be lighter and avoid the vulnerable trailer but had its own flaws. First was the lack of armament as the hull weapon had been replaced, and the turret weapons had been lost. This would receive separate consideration for a solution. The second problem was the profile. A turretless Tiger would draw significant attention and be an obvious target on which an enemy could focus fire.

Certainly, production would not have been a significant issue as the modifications were modest but the whole concept had to be called into question. Major General Thomale was a fan of the flamethrower but only in limited circumstances. Specifically, he liked them on small, light, and maneuverable vehicles which could target the odd stubborn strongpoint and the Tiger I was neither small, light, nor particularly fast even with a turret removed. His second point was also valid. With its main gun, the tank could pick off the enemy at combat ranges up to 2,500 metres meaning a significant safety distance from their fire and, with 80 rounds, could do so many times. A flamethrower meant getting very, very close and offered relatively few attempts to destroy the enemy. Despite the limited advantages of the system, he was therefore against it.

The flame thrower system designed could still be used, but would have to be mounted on something smaller and lighter instead, and the Jagdpanzer 38 was selected as the replacement. Nonetheless, the idea of a flamethrower on the Tiger I was not over.

On 19th March 1945, despite the extremely dire war situation, the project, named ‘Flammenlage auf Tiger I’ (Flame mounting on Tiger I) or ‘Schwerer-Flammpanzer auf Tiger I’ (Heavy flamethrower on Tiger I) was still being listed as a project under development and Hitler ordered Maj.Gen. Thomale to fit the flamethrower system to a turretless Tiger I with the second idea of increasing the thickness of the armor on the front. Quite how much additional armor was meant to be added is not clear nor how it was to be done, but perhaps something akin to the method used on the Ferdinand/Elephant is the best approximation as to which would have been adopted. The Sturmtiger was similarly up-armored with an extra 50 mm plate, which suggests the frontal armour of the Schwerer-Flammpanzer auf Tiger I could have been increased to around 150 mm across the front, a lot less than Hitler might have wanted but certainly a significant improvement.

The original Tiger (P) armor was significantly improved with heavy armor plating bolted to the original front to improve protection. Source: Jentz and McKaughan
Prototype Sturmtiger with 50 mm thick additional front armor plate bolted on the lower front section.

Further progress was still reported into the final days of Nazi Germany, with an update from Wa Pruef 6 on the project as late as 3rd April 1945. In this report, Obert Holzhauer (head of Wa Pruef 6) reported that, following Hitler’s orders, the first steps in putting together this experimental heavy flamethrower on a Tiger I had taken place at Wegmann, Kassel on 21st and 22nd March with completion of the project estimated by 15th April. The Tiger I to be used had been dispatched by train from Kummersdorf on 17th March but, due to enemy bombing, had been delayed until 3rd April 1945. From Kassel, the vehicle was then sent to the firm of MIAG at Braunschweig for assembly there under supervision of men from Wegmann.

This additional movement and Allied bombing meant that the target completion date of 15th April was missed and the vehicle was never completed. Likely, work on actually fitting the system was never even started before Allied forces overran the facility. This is confirmed by a British intelligence report of the time which stated:

…It is believed that this equipment never progressed beyond the experimental stage and no specimen has yet been recovered….

– War Office. (26th July 1945). Technical Intelligence Summary Report 182 Appendix F ‘Flame thrower mounted on Pz.Kpfw. TIGER MODEL E (Sd.Kfz.181)’

System

The new flame-system that was to be fitted to the Flammenlage auf Tiger I reverted back to using compressed nitrogen and special reduction valves (obtained from the Kriegsmarine) which raised the pressure output from the tanks. This meant that this new system had abandoned the motor-driven-pump system. In this way, the pressure of the system could be raised from 1.52 to 1.72 MPa (15 to 17 atmospheres) to 2.03 to 2.53 MPa (20 to 25 atmospheres). With this increased pressure, the system could deliver a jet of burning fuel out to a range of 120 to 140 metres. A pair of 400-litre fuel tanks* would be fitted on the inside (there was more room because no turret was required), providing enough fuel for 16 to 20 bursts, meaning each burst would use about 40 to 50 litres of fuel. At 2-3 seconds per burst, this means the system delivered about 20 litres per second.

The fuel was different to what had been used before. Koebe, when asked at the end of 1942 to design a long-range flamethrower for use on the Porsche-Maus, proved unable to develop a system with a range of more than 100 m. Even then it would have required a flame-nozzle (Spritzkopf) 22 mm wide and would have used 33 litres of fuel per second propelled by a 30 hp engine driving a pumping system. To project a flame even further would require a narrower (12-14 mm) nozzle, but the jet would disperse with range. To go further, therefore, the fuel needed to be thicker and it was this factor which meant a pump could not be used. Even with a range of 140 metres, this was still not ideal and Hiter, in March 1945, still wanted a thicker fuel to match the type used by the British on their flamethrowers, but there would be no time to develop an even thicker fuel. The projector itself, when fitted into the front of the Tiger, would have had only limited traverse. A range of motion of just 10 degrees in all directions was possible.

*(A British report from July 1945 on the project reported a single 300 litre tank, suggesting just a single fuel tank was found with the remains of the system when it was recovered and mis-estimated in volume)

Given that this project was relatively crude, it is hard to know exactly how many men would have been required to crew it, but some things are known. For example, the tank would have had to have kept its driver, located in the front left. Without any kind of remote-control over the direction of the flame-projector, the flame-projector located in the front right would need manual operation too and this would have meant the retention of the man who would usually operate both the hull machine gun and the radio. He would have been the flame-operator and likely still the radio operator too, although it was also identified that flamethrower tanks should have a second radio set in order to coordinate with supporting vehicles. This would suggest the use of a Panzerbefehlswagen Tiger hull which was fitted with both a Fu 5 and Fu 8 (Sd.Kfz. 267) or Fu 7 (Sd.Kfz. 268) radio sets, although on the Panzerbefehlswagen Tiger the additional set was fitted into the turret and would have to be relocated within the hull. No loader was required nor was a gunner, but a commander would certainly have had to be retained in order to coordinate the operation of the vehicle, which would therefore indicate a crew of 3 men. Even with the removal of the turret and ammunition, the two 400-litre tanks required would have taken up a lot of the internal space and it is doubtful there would be room for a fourth man and, in any case, there was no clear role for him anyway.

Automotive

As the vehicle was based upon an existing Tiger I hull, there were likely no changes made to whichever hull was to be used. As the Tiger I had gone through production, various minor changes were made to some internal and external fittings. Some were fitted with special air filters at the back, and others not. Early production Tiger I vehicles received the 650 hp Maybach HL 210 650 hp petrol engine whilst later vehicles received the 700 hp Maybach HL 230 petrol engine. Early production Tigers used rubber-tyred road wheels but these were later replaced with a more resilient steel-tyred type. Without knowing which hull was to be used, it is impossible to know exactly what the Schwerer-Flammpanzer auf Tiger I would have looked like, but the essentials of the automotive system would be identical.

Layout

Changes to the Tiger I hull were relatively modest. Removal of the turret meant leaving a large hole in the roof of the tank which was obviously a serious hazard in combat so this would have been covered with a large armor-plate. Already discussed is the additional armor on the front, although how this might have looked around the machine gun mounting is unclear. Other than these changes and the interior changes, like the removal of the ammunition racks etc., there would have been few changes inside and most of the work would have been done on the roof. For the prototype, it is possible that just a single plain disc of metal welded or bolted over the hole where the turret would have sat would have been employed. This would have retained the front crew hatches but meant that a commander in the back would have been unable to get out except by these front hatches. Given the hundreds of litres of fuel he would be sat next to, this seems highly improbable for any design which would ever have been authorised for production and the description in the British 1945 report provides an additional clue.

Other Armament

Whilst with no turret and hull machine gun the vehicle might seem otherwise unarmed, it was to get a new machine gun, most likely either an M.G.34 (Maschinengewehr 34) or M.G. 42. This would not have been mounted within the vehicle, but this time mounted externally. This would have been controlled from inside, again supporting the proposition of a third crew member, and would have been mounted on the outside of the cover plate over the turret-hole.

The mounting of such a weapon was certainly not a new idea and was mounted on various Sturmgeschütz in the form of a 7.92 mm M.G. 34, fitted with a 50-round drum mounted behind a short and sharply curved gun shield. Under the gun was a small optical sight which permitted the man below the armor to see where he was firing. Reloading however, had to take place externally.

Roof-mounted remote-controlled weapon station as featured on a Jg.Pz.38t (left) and from an Allied Intelligence Bulletin (right). Source: pzfahrer.net/hetzermgs.html and Intelligence Bulletin May 1945

In order to provide any value to the commander, he would have needed to be provided with some optics as the small optic on even the roof-mounted machine gun would be wholly inadequate for the purposes of command. A hatch would also have been required for observations, access or egress to the vehicle, changing barrels, or reloading/clearing stoppage on the machine gun. Despite the description of the “single continuous roof plate”, it would appear that any development of this vehicle would have needed to include at least a moveable optic and hatch for him, or even just a repurposed tank cupola.

One extra piece to consider is that the Tiger was fitted with a self-protection system launching S-mines to protect against enemy infantry. As this Schwerer-Flammpanzer auf Tiger I was, by definition, having to get very close to the enemy in order to use its primary weapon, it would be logical to assume that this type of system would have been adopted for any production of the Schwerer-Flammpanzer auf Tiger I even if the prototype being assembled did not have them. Further, a lot of flame throwing vehicles used by the Germans carried smoke-candle launchers in order to create a smoke screen to protect them from enemy observation. Here again, the addition of smoke grenade launchers on the Schwerer-Flammenpanzer auf Tiger I is a very reasonable assumption as once it had ‘flamed’ its target it would need to withdraw and a smoke screen provides ideal screening during such a manoeuvre.

Conclusion

The overall idea was not a bad one. A flamethrower certainly had some practical military value and served as a potentially very effective psychological weapon against the enemy too. This fact was reinforced in February 1944 by considerations from Panzer Grenadier Division ‘Grossdeutschland’, which recommended the use of a motor-driven ‘howling siren’ to accompany the use of the flamethrower to maximise the demoralisation effect.

Early flame-throwing attempts had been too small (Panzer I), too lightly armored (Panzer II) and too short in range (Panzer III et al.). A heavy flamethrower paired with a heavily armored hull from the Tiger I seems like a system which could have fulfilled the requirements but it was simply flawed in premise.

With very little development time on hand and with the progress of the war going so badly, this was a weapon system which was not going to enter production. The days of assaults against fixed enemy positions like bunkers and trenches, for which a flamethrower is best suited, were over by 1945, as most of the fighting was defensive in nature. The Schwerer-Flammpanzer auf Tiger I was never finished so no photos of it exist and whatever plans may have existed for it are believed to have been lost. Outside of reports, both German and British, the project remains unknown, and the reader is therefore reminded that the discussion over the vehicle is speculative, as is the artist’s rendering.



Illustration of the Schwerer-Flammpanzer auf Tiger I (Flammanlage auf Tiger I – ‘Flammpanzer VI’’) based on existing descriptions. Modified by Pavel Alexe, based on wok by David Bocquelet.

Sources

Doyle, H., Jentz, T., Sarson, P. (1995). Flammpanzer German Flamethrowers 1941-45, Osprey Publishing, UK
Doyle, H., Jentz, T. (2011). Panzerkampfwagen III Umbau. Panzer Tracts, Maryland, USA
Jentz, T., McKaughan, J. (1995). Elefant Panzerjager Tiger (P). Darlington Productions, Maryland, USA
Jentz, T., Doyle, H. (2008). Panzer Tracts No.6-3 Schwere Panzerkampfwagen Maus and E 100.
US War Department. (May 1945). Intelligence Bulletin Vol. III No.9. War Department, Washington, USA
War Office. (26th July 1945). Technical Intelligence Summary Report 182 Appendix F


Categories
WW2 American Prototypes

Chrysler’s Improved Suspension M4A4

USA (1942)
Medium Tank – Blueprints Only

The Medium Tank M4A4 Sherman was an improved variant of the M4A3. The goal of the tank was to increase the speed of production of the M4 by using a new multibank engine and with a hull made from 5 pieces instead of seven. The longer and more complex engine would mean an increased length of track on the ground for improved performance of the M4A4 on soft ground, yet despite this, the M4A4 was not adopted by the US Army for use overseas. Early in the development of the M4A4, consideration was given to making us of the longer hull to improve the suspension. This led to the idea of using the ‘Christie’-style suspension from the T4 Medium Tank on this new Sherman. Whilst the M4A4 was built in large numbers and saw extensive service during World War 2 and later, the idea of using this ‘big-wheel’ suspension never left the drawing board.

M4A4 Sherman with the Vertical Volute Suspension System (VVSS) which Chrysler were investigating the replacement of with an improved big-wheel form. Photo: Mark Nash

Development

The design of the M4A4 began in February 1942. This new Sherman was going to be more mobile than the M4A3 by using the 435 hp Chrysler A57 multibank petrol engine. The selection of what was actually 5 engines fitted together created a crowded space within the engine bay, which necessitated a slightly longer hull than the M4A3. This was considered a tradeoff that could add a large number of tank engines into the supply chain which would aid in meeting their production targets. Further, the hull of the M4A4 was simplified, as it was made in fewer parts than the M4A3 (5 instead of 7), and featured a 3-piece final drive housing on the front instead of the single-piece final drive housing on the M4A3. This would improve the speed of repairs and maintenance on the tank although, initially, the complex engine arrangement had been unreliable.

Lengthening the hull by 11 inches (279 mm) in order to accommodate the engine also meant that the suspension would have to be lengthened. The M4A3 had used three pairs of volute spring suspension (Vertically Volute Suspension System – VVSS) and these could be spread out more along the slightly longer sides of the M4A4 or a new suspension system could be considered instead. This prompted a very short study by Chrysler, the design agent for the M4A4, to try and improve the performance of the tank by way of an improved suspension system. The system to be investigated was a modified version of that trialled on the T4 Medium Tank.

Rather than refit the three VVSS units, spaced out along the side, the idea was now to use five large road wheels connected on horizontal crank arms. Springing for the wheels was delivered by means of vertical coil springs mounted on the outside of the lower hull. This has been described variously online as being a ‘Christie Sherman’ or ‘Christie suspension’ but it really is not. The Christie patent for his system had already been sold off by then as well as licensed off to countries like Great Britain and the Soviet Union. One of the dominant features of Christie’s suspension design was the suspension springs operated within a double-wall cavity along each side of the tank. This system was adopted and adapted for use in tanks such as the British A.13 and Soviet BT-5 and remained in use on some tanks through to the end of World War 2. The British Comet, for example, was the last British tank to use a version of this system. This was not the case for this M4A4. Here, the springs would be mounted externally.

Christie, by February 1942, was almost a dirty word in US armor circles and had no formal involvement with the US Army. His last official contact had been with the Ordnance Department in March 1939 and ended when he had stormed out of a meeting in a tantrum when his demand for large orders for his tanks was rejected. He had stomped off saying he would go and see President Roosevelt and with that had ended any prospect of formal consulting work.

Consequently, attributing his name to this design would be incorrect. If there is any doubt on the matter, the somewhat awful book ‘Steel Steeds Christie’ published in 1985 by his son Edward and which makes numerous fallacious claims, makes no claim to this design. The T4 suspension design was certainly based on the work of Christie, but the first conceptualized drawings for a sprung suspension-arm suspension for the M4, prepared by the Ordnance Office in February 1942, had already departed from this arrangement.

T4

The T4 Medium Tank, built by Rock Island Arsenal in 1935 and 1936, weighed just 13.5 tons (12.2 tonnes). Different versions of the T4 were trialed between 1935 and 1940 when it was declared obsolete, but the key feature of the design was the four large road wheels on each side. The suspension of the T4 was certainly based on the suspension designs from Christie, but it did not use Christie’s patents. The track for the T4 was also a short-pitch type track 12 inches (305 mm) wide.

Medium Tank T4 showing the 4 large road wheel design with no return rollers. Source: Hunnicutt

The T4 weighed just 13.5 tons (12.2 tonnes), whereas the M4A4 would weigh 34.9 tonnes (31.6 tonnes), more than double the weight of the T4, so using the same suspension required changes. The T4 used just 4 wheels on each side, which would be inadequate for the extra weight of the M4. Thanks to the longer hull of the M4A4 though, 5 of these large-diameter wheels could be fitted on each side. The second change came about after the initial drawings from the Ordnance Board. Those drawings had shown the five, closely positioned wheels, each mounted on an individual arm with a corresponding spring cylinder angled forwards. To meet the increased weight of the M4, these springs had to be changed too. The solution here was to adopt heavier coil springs and to mount these vertically along the outside of the lower hull of the tank under the sponsons.


First plans for a T4 Medium tank-style suspension on the M4 Sherman, circa February 1942. Note the suspension springs are angled forwards rather than vertical. Source: Hunnicutt

Tracks

The adoption of the T4 style wheels was also met with the choice of a wider version of the T4 track. This single-pin track was 18.5 inches (470 mm) wide, wider than the standard M4A4 track and the original T4 track, and used a center guide to prevent lateral slippage. With 93 track links per side (compared to 85 on the T4) and the larger, heavier wheel, this new M4A4 was significantly heavier than the original volute-suspension M4A4 by 3,080 pounds (1,397 kg).

The volute-suspension M4A4 used either the T48 or T51 83-link 16.56 inch (421 mm) wide track with a ground contact length of 160 inches (4,064 mm), which was substantially longer than the M4A3 at 147 inches (3,734 mm). Using this T4 style suspension, the track length on the ground was only fractionally longer than that of the M4A3, at just 148 inches (3,759 mm), yet despite this shorter length of track in contact with the ground than the volute-suspensioned M4A4, the wider track made up for this and kept ground pressure to just 14 psi (96.5 kPa).

Front view of the Chrysler sprung swing-arm suspension M4A4 shows the width of the external springs on the sides of the outer lower hull (left), and with the additional width of the spring highlighted in pink (right). Source: Hunnicutt and Author respectively

With the new spring system fitted to the outside of the lower hull, this meant a lot of space was taken up under the sponson on each side. Consequently, the tracks and wheels would be further out than they would be if it had retained the VVSS system. This would have posed some additional issues regarding the transportation of the tank due to its increased width, about 450-470 mm wider than the M4A3 due to the projections of the track and the lack of space in which to add grousers to the inside of the track.

With the new spring system fitted to the outside of the lower hull, this meant a lot of space was taken up under the sponson on each side. Consequently, the tracks and wheels would be further out than they would be if it had retained the VVSS system. This would have posed some additional issues regarding the transportation of the tank due to its increased width, about 450-470 mm wider than the M4A3 due to the projections of the track and the lack of space in which to add grousers to the inside of the track.

M4A4 with VVSS (left) compared to M4A4 with T4 Style Suspension (right) showing the additional width of the M4A4 (not to scale). Source: Hunnicutt
M4A4 with VVSS (top) compared to M4A4 with T4 Style Suspension (bottom) (not to scale). Source: Hunnicutt

One final note of difference between the suspension systems on the M4A4 are the return rollers. Easily overlooked, the VVSS system used a small return roller angled back from the suspension bogie which served to hold the track off from fouling on the top of the bogies. No such rollers were drawn on the T4 suspension units to support the track. The angle of the track, as it descended from the front sprocket to the rear idler, would likely contact the top of the last roadwheel but other than that it was unsupported .

The final product. Five large diameter T4-style road wheels and vertical coil spring suspension on the M4A4. Note that the mantlet is misdrawn and should be further back, towards the turret front. Source: Hunnicutt

Conclusion

Despite the fact that the T4-style suspension was found by engineers at Chrysler to be workable, it was not pursued. The volute system was not ideal but it was simple and reliable. In the short-term, the volute-spring system was retained, although work on improved suspension for the M4 continued. No versions of the Chrysler vertical coiled spring suspension M4 were ever built. Despite 7,499 M4A4s being built, it only saw limited service with the US Army anyway, restricted mainly to training duties. It did, however, find extensive use overseas particularly with the British, where it was known as the Sherman V.



Illustration of Chrysler’s improved suspension M4A4. Illustration by Andrei Kirushkin, funded by our Patreon Campaign.

Specifications

Dimensions 6.06 m x 2.62 m (hull, 3.07 m to 3.09 m wide over tracks) x 2.74 m
Total weight, battle ready 72,780 pounds (36.29 US tons) (33 tonnes)
Crew 5 (commander, driver, co-driver, gunner and loader)
Propulsion 435 hp Chrysler A57 multibank petrol engine
Speed (road) 35 mph (56 km/h)
Armament M3 75 mm gun in M34 mounting
.50 calibre M2 AA machine gun
2 x .30 calibre M1919A4 machine guns
Armor 1.5 inches (38.1 mm) – 3 inches (76.2 mm) – 107.95mm

Sources

Armor Magazine, November-December 1991. Christie’s last hurrah.
Christie, E. (1985). Steel Steeds Christie. Sunflower University Press, USA
Gabel, C. (1992). The US Army GHQ Maneuvers of 1941. Center of Military History, United States Army, Washington D.C., USA
Hunnicutt, R. (1977). Sherman – A History of the American Medium Tank. Presidio Press, USA
Icks, R. (1969). The Fighting Tanks 1916-1933. We Inc. USA