In 1962, the US Armor Association launched a competition for the design of a next generation of Main Battle Tanks (MBTs) to replace the M60 Gun Tank in light of advanced Soviet vehicles which were being developed. The goal was to gather ideas as to how people thought the tanks of 1965-1975 might look and left the various designers a lot of freedom in terms of armament and propulsion. Many designs were sent in from around the world but one very close to home came from a serving US soldier, David Bredemeir, based at Fort Knox, the home of the US School of Armor at the time. This design was to eschew conventional suspension, layout, and armament and produce a missile carrier capable of destroying any future Soviet threat. Named the ‘M-70’ (no connection to the MBT-70), presumably for the anticipated in-service date, this vehicle provides a semi-professional glimpse at some of the thinking of the era.
The basic layout of the M-70 was a long slender tank. The engine, a “long slender gas turbine”, was positioned alongside the driver at the front. The turbine would power the front-mounted transmission.
The M-70 was not to be a conventional gun tank. Bredemeir eschewed the conventional cannon approach for his design and put the offensive capability for the tank in the hands of anti-tank guided missiles. This design choice was based upon the logic that it would be able to fire before an enemy tank could and to ensure a first-round hit each time. The result was that the tank was to carry a battery of 8 anti-tank guided missiles (ATGM) in each ‘fender’, the sponsons along each side above the tracks. As the missiles traveled slower than a conventional shell, they could be fired in the general direction of the enemy even without aiming, with this process then being picked up by means of the guidance as the vehicle stopped. There would then be time to guide the missile onto its target before the corresponding enemy tank had had time to stop, aim and fire its main gun. Another launcher was retained in a rotatable turret at the back of the vehicle and between 50 and 60 missiles could be carried. Storage was facilitated for them, as their fins were all spring-loaded to fold down. Of those 50-60 missiles, 20 were to be stored in the turret.
Various types of missiles were proposed, including smoke, chemical, heat-seeking, and even atomic rounds, guaranteeing these missiles were capable of taking on even the heaviest of enemy armor. The heat-seeking missiles also enabled this tank to counter enemy aircraft and it could track them itself too with a built-in onboard radar. A machine gun was mounted on the commander’s cupola.
The M-70 was to use a three-man crew consisting of commander, gunner, and driver, although the gunner also served as a radar operator. When the gunner was busy loading the missile tube, the commander could take over his duties. Of the three crew, the driver would be at the front, leaving the commander and gunner in the turret at the back. The gunner, situated on the left, would be able to operate the missile launch-tube centrally as well as the radar, and when he was otherwise engaged, the commander could take on the gunner’s duties. The commander sat in the turret on the right-hand side and had his own cupola with a machine gun.
Being lower than the M60 Gun Tank would give the M-70 a higher chance of survival on the battlefield, as it would be less likely to be hit. It also meant a lighter and more maneuverable tank but it still needed armor. The result was that the M-70 was to be made out of aluminum. This, in turn, would keep the overall weight down to 20 to 25 tons (18.14 to 22.70 tonnes)
The suspension for the M-70 was a ‘two-stage’ system, with the tracks and road wheels divided in half and connected together via a single leaf-spring holding them to a beam that ran the full length along each side. Each of those beams was then connected by a pivot arm at the front and back of the tank to a connector on the opposite side. The hull itself was not mounted directly to these track units but held via coil springs from each end of the beam instead. Only the driving axles for the sprockets would directly link the hull to the tracks units. This double-spring system was felt to provide maximum comfort. Small road wheels would spread the weight of the tank along its track and also serve to keep the overall height of the vehicle down.
During the 1960s, faced with the enormous growth in power of anti-tank guided missiles, many were speculating it meant the end of the conventional tank. Likewise, the potential of ATGMs outstripped the anti-armor potential for large caliber guns with the advantage of being significantly smaller and lighter. Many countries would consider and even develop ATGM-based tanks during the Cold War, but just like the US Army, they were constrained by budgets, thinking, and a conservative attitude of trying to keep developments relatively simple. The M-70 offered superior firepower to the M60 in a much smaller vehicle but in 1962, this gun-launched missile concept was already underway on the M551 Sheridan. It was never to work satisfactorily for that tank and the M-70 offered little to warrant development.
Post World War 2, the United States had a glut of tanks including large stocks of M4 Shermans and new designs such as the M26 Pershing. There was, as a result, little impetus for new vehicles, even though design work, if anything, increased apace at this time.
Throughout the 1950’s, US tank designers were looking at every aspect of the problems of tank technology, from armor to propulsion and armament. Whereas a lot of development had made great strides during this time in other areas, armor was still fundamentally based upon large steel castings. Various ideas though had been tried, including compositions with glass in armor cavities and even work on bar armor to defeat incoming projectiles and the increasingly common HEAT-type warheads.
By the early 1960s though, even with a new generation of Main Battle Tanks (MBTs) at hand, the US was short of a light modern tank that was air-transportable, amphibious, well-armed, and well protected. Obviously, this is a holy grail of tank design, light-enough weight to be air-transportable but with enough armor protection to be useful in direct battle rather than just scouting or skirmish roles. The tank which was to become the M551 Sheridan was in development but this was not the only possible light tank in development at the time. Another design from the Forsyth brothers was also being planned, and this vehicle was a technological step well ahead of anything the Sheridan offered. The first glimpse of this vehicle came in a competition held by the US Armor Association in 1962, with an entry deadline of August that year.
The first thing to address in looking at this design are the designers, John and Robert Forsyth. John and Robert were brothers who were engineers living in California and worked at the Vehicle Systems Development Division of the Lockheed Aircraft Corporation in California. Over the years, they designed and developed various transportation-related vehicles, amongst other things. These included a large bus for cars to travel in and various forms of unusual traction machines including a tri-wheeled amphibious vehicle and articulated machines.
Whether their tank design was already being considered prior to the Armor competition of 1962 is not clear, but it was certainly submitted, meaning it must have been ready before the end of August 1962.
The Need For a Light Tank
Despite a multitude of light tank designs considered during various conferences during the 1950s, it was not until January 1959 that work had begun in earnest of a new light combat vehicle under the designation AR/AAV (Armored Reconnaissance/Airborne Assault Vehicle). The specifications demanded of that design were presented in July 1959 by Ordnance Tank Automotive Command (OTAC). That vehicle was going to have to replace the existing stock of M41 light tanks, the M56 self-propelled gun and supplement/work alongside the existing main battle tanks and armored personnel carriers in service.
To meet this demand, a pilot vehicle was prepared by Aircraft Armaments Incorporated (AAI) with a 3-man crew tank in the 10-ton (9.1 tonne) class. Another company, Cadillac, designed a vehicle with a four-man crew and a little heavier. Neither of those vehicles though, as obvious by the incredibly low weight, had any reasonable protection outside of against small arms. Even so, the Cadillac proposal, although selected for development, was still woefully under-protected even outside the weight limit imposed. As a result, the allowance for weight was increased to 15 tons (13.6 tonnes) and was designated AR/AAV XM551, the progenitor of the M551 Sheridan. What that design sacrificed in height and size it made up for in armament, with a 152 mm main gun capable of firing a large HEAT (High Explosive Anti Tank) round as well as the Shillelagh missile with a HEAT warhead. Both of those weapons were capable of taking on even the heaviest contemporary Soviet armor and also provide fire support for airborne troops. Other weapons under consideration at the time were a conventional 76 mm, 90 mm, 105 mm, and even 152 mm guns, ENTAC (ENgin Téléguidé Anti-Char) (to supplement any conventional gun), TOW (Tube-launched, Optically-tracked, Wire-guided), or POLCAT missiles.
The first pilot XM551s were delivered in June 1962 for testing, with more pilots following in 1963, 1964, and 1965. Despite teething problems, the design was authorized for production and contracts issued in April 1965. The M551 went on to provide decades of service for the US military in various conflicts but it never really lived up to expectations. The armor was always inadequate and the firepower from the gun/missile system never really worked well.
A contemporary design though, offered some solutions to what became the flaws in the M551 Sheridan, whilst at the same time adding another layer of complexity to meet the demand to replace the old and obsolescent M41 Walker-Bulldog and M56 Scorpion vehicles in service. Providing a main battle tank class vehicle at a significantly reduced weight, this design was supposed to add mobility as it could go places a conventional tank, light or otherwise could not go.
Having won the tank design competition with their design at the end of 1962, the Forsyth brothers and Lockheed Aircraft Corporation were anxious to secure and market the idea. The result was an embodiment in the patent application filled in January 1963, but there was nothing in that application other than the layout.
What it showed was a small tank with 5 road wheels on each side, topped with a low-profile rounded turret. Inside that turret can be seen one large caliber gun and a smaller secondary armament. Most striking in that design though is what is behind the tank, a trailer. Not just a trailer in fact, but another tracked hull, with 5 road wheels but where the armored body is taller, reaching nearly the height of the turret of the preceding vehicle. The two sections connected together through an articulated joint. The details of the articulated design would be made clear in a following application filed in July that year.
The articulation was carried out by means of an assembly consisting of two rungs, the outer of which has two arms connected to the hull of one vehicle which controlled the pitch and roll between the two sections. The inner ring was mounted by means of an internally rotating ‘shoe’ to a yoke which was fixed rigidly to the other vehicle. In this way, the coupling allowed for a controlled degree of rotation between the two sections as well as movement sideways (as encountered when steering) and vertically (as encountered when climbing or descending).
The armor in the 1962 Armor competition was described as a steel and aluminum alloy with a maximum thickness of 76 mm to 150 mm (3 to 6 inches). This was clearly subject for more thought and the focus of the design submitted for patent in July 1963 was the armor. Instead of relying on a homogenous steel plate that was face hardened and was heavy and vulnerable to shaped charges, the Forsyth brothers envisaged a new system. This system consisted of a series of layers, a first and second layer of rigid armor spaced apart from each other which the cavity between them filled with a multitude of different armor panels, which were themselves held apart by a filler material proposed to be cellular or a foam-type material. This armor-system extended across the entirety of the front of the tank, covering the glacis and lower hull, but also along the full length of the upper hull side sponsons over the tracks. The lower hull, in order to save bulk, was just the single-thickness stiff section. Likewise, the roof was a single thickness of metal as was the rear.
The panels inside the armor cavities were suggested as being made from a variety of possible materials, including glass-fiber or metal fabric laminated together, coated with flexible epoxy-urethane resin. Other epoxy resins, polyurethane and plastics could also be substituted. The filler material between those panels served to hold them apart and offer rigidity and was to consist of polyurethane resin too. The difference between this resin filler and the other resin used was that this filler-resin was also to contain cyclohexylstearate or dimer acid, and a lead, cadmium, or boron compound (i.e. lead oxide, cadmium oxide, boric oxide) as protection against neutron radiation. In other areas where this filler did not need to be used throughout the cavity, it was to be substituted with foam, as this was a good thermal insulator and provided buoyancy.
As an aside, Forsyth and Forsyth also considered that this armor was suitable for consideration on ships and submarines. The projected weight for both parts was just 21 to 22 tons (19.00 to 19.96 tonnes) for the steel/aluminum armor version and fro, 24 to 32 tons (21.77 to 29.03 tonnes) for the composite armored version, depending on the exact composition. The composite armor-option was a significant improvement over the original steel and aluminum option and provided the design with substantially more protection than that of the Sheridan against both kinetic energy and shaped charge munitions.
As shown in the patents, there were two weapons mounted on the tank, and later, a third weapon mounted on the following unit. The tank’s weapons consisted of a single large-caliber gun of an undisclosed size in the patent, although it bears a close resemblance to a gun like that on the M551, the 152 mm. Bearing in mind the requirements from the army, as stated before, included 76 mm, 90 mm, 105 mm, and even 152 mm guns, ENTAC (to supplement a conventional gun), TOW, or POLCAT missiles, one of those would have been chosen and what is shown is too large for either the 76 mm or 90 mm guns. In their competition entry, the Forsyth brothers were clear that they planned a 155 mm gun as the primary weapon, capable of firing rocket-assisted projectiles. The secondary armament, as it appears in the patents, appears to be a cannon, but is only described as the secondary armament for anti-personnel purposes. No mention is made of the third gun at the back, which could be assumed to be a machine gun. In their competition entry, the secondary gun is confirmed as a 20 mm Hispano-Suiza HSS 820 automatic cannon in the front vehicle and the small turret at the back is confirmed to take a 7.62 mm Vulcan-type machine gun.
The M551 was to have a crew of four, as the use of a three-man turret was seen as having value in combat. The design from Lockheed though went away from that idea and back to a three-man crew with just two in the turret. The two men, commander/gunner, and gunner/loader were seated on the left and right, respectively. The driver, lying supine to reduce the overall height of the vehicle, was located on the front left of the hull, with the engine to his right. Although being self-powered and able to operate independently of the following unit, the unit behind contained more men. Four more men in the back acted as a small armored personnel carrier team attached to the main tank and accessed it via a door at the back. They could egress the vehicle to fight or carry out tasks dismounted, and in the final patent publication’s drawings, this following unit had gained a small turret with a gun so as to provide additional firepower. As part of a platoon of such tanks, the men in the rear sections would end up being a unit 15 to 40 strong without the need for additional APC’s to follow.
Automotive and Suspension
The engine for this first section of the vehicle was located in the front right of the hull and centrally in the second section. It is described only as “a piston unit [conventional petrol or diesel engine] or a gas turbine” which drove an A.C. electrical generator. That electrical power was then delivered to the back of the tank (in the case of the lead unit) where traction units drove the sprockets. On the trailing unit, the same system was used except that the electrical traction units and sprockets were at the front. Steering was electro-hydraulic, able to adjust power to the tracks on each side of each section to vary the turning moment applied but also allowed for steering forces to be applied through the coupling hydraulically.
Suspension for both sections was by means of a flat band track mounted on long-pitch, large-diameter road wheels, although the designers did suggest that if tracks were not suitable that a multi-axle wheel system could be substituted instead.
One advantage of this arrangement of power with two independently powered sections connected by an articulated joint was flexibility. Either vehicle could operate completely independently or together. If one unit failed or broke, the other could push or pull it along, reducing the chances of the design becoming stuck or crippled. Further though, the independence of the electrical transmission provided additional benefits. The sections could be split and have power sent from one half to the other via cable even though they are not attached. This means that the vehicle did not have to float across waterways but instead could submerge and receive power from another tank on the bank. Once it got to the other side, it started up and sent power to the following tank in a system very similar to that adopted for the German Maus in WW2. It made loading onto aircraft for transport easier too.
The design from Messrs. Forsyth and Lockheed was, in many ways, ahead of its time. During the early 1960s, the concept of using composite armor was still new thinking. There were, however, serious problems to overcome. The coupling concept was not new, ideas for coupled tanks date back to 1915, and although the coupling in 1962/3 was undoubtedly better designed than the ones from 1915, it was still not a perfected technology. Lighter than the M551, this design offered increased protection and capability and the potential for improved firepower, but it was unlikely to have ever received serious consideration. By the time the first patent was filed, the US Army’s eyes were on the XM551 project, which offered a lot of what they wanted without having to use new and as of yet unproven technologies. The potential offered by this design was thus lost, it received no orders and was never built. Coupled vehicles would continue to be examined by a variety of countries for a variety of purposes, as would coupled tanks and electric drive and composite hulls. This design, however, seems to be the first design to combine all of these elements in one.
The tracked version of the Lockheed/Forsyth Tank
The wheeled version of the Lockheed/Forsyth Tank
These illustrations were produced by Andrei Kirushkin, funded by our Patreon campaign.
1.83 m (72”) high
21 – 22 tons (19.00 – 19.95 tonnes) (aluminium/steel armor version) up to 24 and 32 tons (21.77 to 29.03 tonnes) (composite armor version) depending on armor selected.
3 (Driver, Commander/Gunner, Gunner/Loader) + 4
Petrol/diesel piston engine / gas turbine, with electric transmission
322 to 483 km (200 – 300 miles)
155 mm main gun firing rocket-assisted projectiles (24 rounds), 20 mm Hispano-Suiza HSS 820 automatic cannon (200 rounds), 7.62 mm Vulcan-type machine gun (2500 rounds)
Steel/aluminium alloy mix 76 to 150 mm thick later changed to composite-type 76 to 150 mm thick
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.
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
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.
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.
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.
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.
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).
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.
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 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.
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.
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.
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.
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.
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
4 (Commander, Gunner, Loader, Driver)
Avco-Lycoming Turbine (Petrol) 1,500 hp (1,119 kW)
41.5 mph (67 km/h) governed
High-hardness-steel torsion bars with rotary shock absorbers
120 mm XM256 smoothbore gun
12.7 mm M2HB QCB heavy machine gun
2 x 7.62 mm MAG58 general-purpose machine guns
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
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.
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.
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 coupledM113s 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).
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.
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.
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.
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.
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.
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’.
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.
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.
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
Total weight, battle ready
103,968lbs (47.2 tonnes) to 106,500lbs (48.3 tonnes)
Minimum 1 (driver), ideally 2 (one in each vehicle)
Specifications (Articulated LVT)
33 ft x 14 ft x 19 ft (10.06m x 4.27 x 5.79 meters)
main engine LCR-V903 890hp, auxiliary engine 100hp
primary automatic weapon in fore section controlled remotely, secondary weapon on commander’s turret on aft section
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
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.
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.
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.
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.
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.
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.
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 compartmentalization 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.
Petrol-Electric (8 Petrol turbine driving 32 high speed homopolar generators)
2 machine guns, cannon, surface to air/ground missiles
Armor Magazine January-February 1963
Hibbing Daily Tribune, 12th June 2011 ‘Everett Philip ‘Babe’ Ridlon
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 bodyM113 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.
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%.
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.
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.
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.
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.
Illustration of the Composite M2 Bradley modified by Pavel Alexe based on work by David Bocquelet, funded by our Patreon campaign.
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.
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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
In 1962, the Cold War was at a peak, with the two great power blocks of the Soviet Union/Warsaw Pact and the United States/NATO facing off across Central Europe. By the 1960s, the Soviets had made significant strides forward in their armored vehicles and possessed both a numerical and, in many regards, a technical advantage over the NATO forces seeking to safeguard Europe.
The US was still maintaining large stocks of obsolete weapons including many from WW2 and had, by the late 1950s, realized the need for a new light tank. That program eventually led to the M551 Sheridan. When the first prototype of that vehicle was published in the summer of 1962, it appears to have spurred some further thought about a replacement or supplemental main battle tank for the US, one suitable for the perceived battlefields of Europe from 1965 to 1975. The US Armor Association issued a design competition one month after the appearance of the M551 for exactly this purpose, to design a new tank.
One of the men who answered the call and submitted a design was Gustave L. Eischen. Eischen is described by the Magazine of the US Armor Association only as being from Luxemburg, with no other details. In the photo above, his uniform and cap badge appear to indicate that he was a member of the Army of Luxembourg and his rank is given as a Sergeant. The Army of Luxembourg at the time was contributing a brigade-sized force to NATO in Europe, with little prospect of beginning its own tank production.
In a newspaper article in Luxembourg published on 7th December 1962, it states that Eischen, a soldier for 8 years and a mechanic in the Luxembourg Air Force, resigned to pursue other opportunities.
Eischen submitted a sketch and a model and claimed to have been working on his idea for several months prior to the competition being announced, meaning it would date to around January or February 1962 at the earliest. He had to submit it by the deadline of August 1962, so it is clearly not later than this latter date.
The design, at first glance, is quite unusual, with four sets of tracks and a steeply angled front and rear in what could be thought of as two half-tanks joined together. This is because the design was to use a pair of air-cooled engines and two drivers, one in each half. Mounted on top of the four two-roadwheel track units, the height of the tank could be varied hydropneumatically.
Having one driver at each end allowed for the vehicle to be driven at high speed safely in either direction without having to turn around. Along with the variable height of the suspension, this would allow a good deal of off-road mobility and a range “triple that of the M60” by virtue of the several ‘special’ fuel cells arranged around the vehicle.
The shape had one more critical advantage too. It allowed for extremely good visibility from the turret both fore and aft and for the vehicle to be equally fightable in each direction.
At just 6 meters long and 3 meters wide, the vehicle would have been almost exactly the same size as the WW2-era M24 Chaffee, albeit slightly heavier at between 24 and 32 US tons (21.8 tonnes to 29 tonnes) depending on the armor thickness selected.
The armament was to consist of either a conventional 75 mm or 90 mm gun, which would provide excellent general-purpose firepower against vehicles and infantry support. For contact with heavier tanks, against which the gun would not be adequate, it was supplemented by a pack of ‘self-homing’ [guided anti-tank] missiles. In order to keep the silhouette as small as possible, Eischen took the unusual step of simply placing the gun and missiles at opposite ends of the turret, facing in different directions. Thus, should a heavier target need to be attacked, the gun would have to be fully rotated to fire the missile. On the drawing submitted, a machine gun, fitted to what is assumed to be the commander’s cupola on the turret roof, is also shown.
Given the low weight – less than 30 tonnes – even at its heaviest, protection would be modest. The M24 Chaffee, a comparative-sized vehicle, had conventional welded steel armor up to 38 mm thick in places. Given the additional weight of the missiles, additional driver’s station and second engine, the Eischen tank would unlikely have been able to mount armor much thicker than the M24 Chaffee. The mention of ‘special’ fuel cells though could imply that Eischen was considering the careful placement of these fuel cells to increase protection for the vehicle, but whatever details he might have provided were not included in the article concluding the competition.
Eischen appears to have got nowhere with his design. It won second place in the Armor competition in 1962, behind the articulated tank concept of the Forsyth brothers. His military career did not pan out either, but a lingering trace of him exists in a patent for a self-supporting element used in the manufacture of prefabricated houses filed in 1971 in Germany. There his home town is given as that of Ettelbruck in Luxembourg.
Eischen’s design featured the significant novelty for 1962 as hydropneumatic suspension for 4 separate track units. The two-driver idea was not particularly new as many armored cars had featured a second (backward) driver before this for the same reason, the ability to withdraw at speed. The armament offered little in the way of novelty too, a conventional 75 mm gun was by 1962 a hopeless concept for anything other than the lightest of armored targets. Even consideration of a 90 mm gun would likely have been of little use against modern Soviet tanks which is why he had added missiles. It is the missiles which are the most interesting novelty of the design as they faced backward, an unusual yet simple solution to a complex problem of mounting a missile battery on a tank.
Illustration of Eischen’s Main Battle Tank produced by Andrei Kirushkin, funded by our Patreon Campaign
6 x 3 meters
Total weight, battle-ready
21.8 tonnes – 29 tonnes)
4 (front driver, rear driver, commander, gunner)
x2, unknown type
75 mm or 90 mm gun supplemented with anti-tank guided missiles, machine gun
Light Combat Vehicle – None built
Prompted by the experiences of the terrible weather and terrain conditions during of the War in Korea (June 1950 to July 1953), in October 1950 the US Army began a collaborative project with the Canadian Directorate of Vehicle Development to produce a highly mobile tracked vehicle platform suitable for a variety of roles. A specific emphasis was placed on use in extremely poor quality ground which could otherwise not bear the weight of a large armored vehicle. Specifically, the purpose was defined as “to study armored warfare to ascertain armor’s probable role in a future war, especially as it may be affected by current trends in technology and tactics, new tank and antitank weapons and new methods of their employment”.
The task, therefore was a huge one. Creating a highly mobile, lightweight, tracked vehicle capable of being used for a variety of combat and logistics roles and able to operate at high speed in sand, snow, or mud.
The variants of the Cobra were various classified as ‘AC’ for an articulated vehicle, ‘CC’ for a conventional vehicle, and ‘AT’ for the articulated vehicle and troop carrier.
The front profile of the vehicles was to be kept as small as possible to ensure it presented as small of a target to the enemy as possible. The tracks on the other hand, would be as wide as possible, nearly touching each other under the vehicle. This removed most of the belly of the design, so that virtually all of the vehicle was above the tracks, unlike other designs, such as the Tracked Jeep or a modified Universal Carrier. The tracks would also be of a new ‘spaced-link’ design to save weight and consist of a main run with 4 road wheels driven from the rear with an additional pair of wheels and tracks, unpowered at the nose of the vehicle.
A final recommendation on the working paper was to investigate the use of a two-stroke multi-bank engine to replace the Hercules JXLD 140hp engine which had been selected. A new engine, it was felt, would reduce weight and improve performance and work had already been done on this subject for a prospective and later aborted 10 ton (10.1 tonne) light tank for which a 180 hp 1,000 lb (435 kg) multi-bank two-stroke unit had already been built in 1938 made from six separate 30 hp engines. Smaller, more powerful and lighter than the Hercules unit, switching to this type of engine would permit an armored roof or other protection to be added or simply improved performance for the Cobra.
The primary armament for the Cobra was to take the form of a recoilless rifle on multiple mounts. The weapons were to be kept loaded at all times when approaching a combat zone due to the time taken to reload it, but could fulfill both anti-tank and infantry support roles adequately.
The weapons selected had to be capable of engaging and destroying an enemy tank with a performance required on defeating 13” (330 mm) of armor plate at 2,000 yards (1,800 m), although accuracy would be assessed at 1,000 yards (910 m) temporarily for the study. As an absolute minimum, anti-armor performance had to at least meet that of the T124 76mm anti-tank gun. In particular, the vulnerability of airborne troops to Soviet armor after being landed meant that the primary user for the anti-tank capability would have to be designed around the US airborne force.
With a desire for at least a 75% fire round hit (with 15 seconds to aim at a target 2.3 metres square at 1,000 yards) being estimated as required to take out an enemy tank before it could fire back and no chance of a second shot in time, multiple recoilless rifles were needed, meaning a minimum of two guns were needed. The two guns considered being the 105 mm M27 rifle (formerly the T19) firing the T-43 High Explosive Anti-Tank (HEAT-T) round at 1,250fps (381m/s) or the newly proposed T136E2 or T137 BAT (Battalion Anti-Tank) gun firing a fin-stabilised projectile at 1,750 fps (533 m/s). With stadiametric range determination with two guns the chances of this first round hit increased to 79%, but this was considered to be an insufficient margin of error. As the Cobra carried almost no armor, it would have to destroy the enemy target first as it could not take any hit in reply.
Three guns firing the T-43 HEAT rounds using stadiametric range determination with one gun firing first and then the second two firing as a pair yielded an increased hit probably of 81%. However, the most effective combination was seen to be four of the then new BAT guns using the same ranging method which increased the probably to 95% at 1,000 yards (910 m) and 75% at 1,280 yards (1,170 m). This unusual method of one shot-adjust-salvo fire was seen as being more cost effective and simpler than the use of a dedicated range-finder which was considered expensive, difficult to adjust, and complex to train with. Multiple salvoes were simple, cheap, and provided a better margin of error. It should also be noted that although the report did not discuss projectiles other than the T-43 HEAT-T round, the M27 rifle could also fire the T268 High Explosive (HE, standardised as the M323), T-269 White Phosphorus (WP, standardised as the M325), T139 High Explosive Plastic (HEP-T, standardised as the M345B1) and M326 High Explosive Plastic (HEP, standardised as the M326) rounds. The BAT was to be an improvement over this M27 105mm rifle, lighter by 61 kg and despite being a ‘rifle’ was actually smooth bore.
The working paper concluded that, with regards to guns, further work should be conducted on improving the muzzle velocity of recoilless rifles in service and that more data should be obtained from firing trials under realistic combat conditions.
Not more than 20% of the weight of the vehicle was to be spent on armor with the heaviest protection concentrated at the front. The armor basis selected was steel ⅝” (16 mm) thick with a maximum of ¾” (19 mm) on the front of some variants. The armor was extremely thin, resistant at best to heavy machine-gun bursts, small arms fire, and shell splinters from 105 and 155mm guns. An alternative ‘light’ basis for armor of just ⅜” (9.5 mm) was also drawn up for the AC-1 design merely to serve as a comparison to the Tracked Jeep and to a modified Universal Carrier. The two thicknesses ⅜” and ⅝” respectively were also considered to be the minimum required to protect against .30 calibre and .50 calibre machine-gun fire but the ⅝” was considered to give the greatest margin of error for protection and was the overall recommendation for armor basis. This provided, according to the designers, complete protection to the front from the .50 calibre M2 Armour Piercing round at 2,930 fps (890 m/s) at any range and to the sides from 350 yards (320 m) for the AC-2 to 1,100 yards (1,000 m) for the CC-2. One final unusual note on the armor was that the hull sections were to be completely cast rather than welded to save weight.
With the articulated (AT and AC) form of the vehicle, the engine sat longitudinally on the right hand side with the driver sat alongside it, in a semi-supine position on the left. This front section of the vehicle held only the driver and engine, behind which was the articulation mechanism to the back half of the vehicle. The back half varied between the various roles to be performed but was also driven by the same engine with the drive sprocket at the front.
Moving large numbers of troops across long distances over rough or boggy terrain with some protection from the elements and enemy fire features prominently in the Cobra design. Various sizes were envisaged for the troop carrier version for 6, 8, 10, and 12 men, in the form of the AT-6, 8, 10, and 12 respectively. The single crew member was sat in the front compartment with the crew section located behind him in the articulated portion of the vehicle. No armament was drawn and the seating positions as shown suggest no option for crew served weapons or firing ports but the report made clear that such weapons could be mounted as desired later. Armor was very thin, just ¾” at maximum, which would be sufficient to protect against heavy machine-gun fire across the front. Even the largest and longest (AT-12) version weighed in at just over 12.25 tonnes which, combined with the very long and wide track run with 610 mm wide tracks would produce a very low ground pressure.
The troop transports had light protection over the sides and none over the top. Removing the roof would allow the troops to fire over the walls and also significantly reduce the weight of the vehicle. At a later date, when other weight savings (particularly the engine) were found, a roof of up to ⅜” thick was considered.
The Cobra AC-1 used a rear-half with 7 wheels and the turret mounted right at the front of this section. Two recoilless rifles were to be mounted on each side with the gunner sat between them. To reload, the third crew member could elevate a protective box at the back to access the venturi at the back of the rifles. This system had the advantage of protecting the loader, but on the other hand, the significant disadvantage that even if only one round had been expended no further firing could take place during reloading on the first rifle. Twenty rounds of ammunition for the rifles was carried in the centre section of this rear portion of the machine permitting up to 5 full salvoes to be fired.
The Cobra AC-2 was shorter than the AC-1 and the rear portion was just 5 road wheels long instead of 7. The turret was moved to the rear instead with the 20 rounds of ammunition stored ahead of it at the front of the section. This arrangement had the advantage of shortening and lightening the rear section but made reloading even more complex, in that the turret would have to rotate fully to the rear in order for the loader (now sat in front of the turret) to reload the rifles from behind.
The Cobra AC-3 sought a different solution to the armament mounting with just 3 rifles mounted in parallel to each other across the left hand side, to the centre line of the rear portion of the vehicle. The gunner and loader sat on the right alongside these guns with the gunner at the front facing forwards and the loader behind him facing inwards towards the guns. Eighteen 105 mm rounds were then stowed under these rifles for the loader permitting up to 6 full salvoes. The mounting for the gun was limited to just 30 degrees each side in this arrangement.
The Cobra CC arrangement was classed as ‘Conventional’ as it was not articulated. Unlike the articulated variants with the engine on the right and driver on the left, this arrangement was to have the engine lying centrally down the middle of the vehicle with the driver on the left and additional crew member on the right. The CC-1 design was just two man but the CC-2 had a third crew member sat in a small turret at the back. Both versions featured four rifles but reloading was much easier on the CC-2 due to this third crew member although it was consequently a longer and heavier vehicle. Seven road wheels were needed on the CC-2 compared to just 5 on the CC-1 and about 2.5 to 3 tonnes heavier depending on whether the CC-2 was to carry just a pair of guns or four. Both designs would be able to carry 12 rounds for their guns though, sufficient at least for 3 full salvoes.
Other Cobra LCCCV variants
With a capable off-road platform, the Cobra would be available for use as a mortar carrier, an anti-aircraft vehicle (drawn mounting a quad .50 cal. AA mount), a rocket launcher vehicle, a cargo carrier (with a 3.5 tonne trailer), an ambulance, communications vehicle, and even a flame-thrower vehicle, although the ambulance and flamethrower vehicles were not drawn.
Three versions of the Cobra were recommended for construction. The AC-2, the CC-2 and the AT-12 were seen as comprising the best ideas for the platform across its combat uses. Sadly, none of these vehicles appears to have found its way into production. The Army would keep using its Weasels for transport in place of the Cobra and, although there were some other vehicles which did enter production with multiple recoilless rifles, such as the famous M50 Ontos, none of these Cobra vehicles made it to production. The articulated vehicle design idea did not go away however, and the most famous of this type of vehicle in use is the Hagglunds BV206.
Illustration of the ‘Cobra’ Light Cross Country Combat Vehicle (Cobra LCCCV) produced by Yuvnashva Sharma, funded by our Patreon Campaign
The United States Marine Corps (USMC) has, as core element of its role, the task of assaulting enemy-held coastlines. In order to fulfill this obligation, they required a form of transport that could get them from the landing ship off the coast to shore quickly and safely. It needed to be fast in the water as it was vulnerable to enemy fire with nowhere to hide and had to protect the occupants to get them onto the beach. It should also be able to deliver supporting firepower to support the Marines in their attack. All that sounds simple enough, but the combination of these demanding requirements was a complex juggling skill to balance the competing requirements.
A Modern Amphibian – 1964
The existing fleet of amphibians dated back to the Second World War and were obsolete. The need of the Marine Corps had not gone away so a new vehicle was needed. As a result the Bureau of Ships (a Department of the Navy) issued a preliminary specification on 23rd January 1964 for an Assault Amphibian Armored Personnel Carrier with a minimum requirement for a forward water speed of 8 mph (12.7 km/h) from tracks or 10 mph (16 km/h) from auxiliary power, a reverse (backing) speed in water for 3.5 mph (6.3 km/h). The vehicle was to carry enough fuel for 7 hours at 8 mph and to manage a forward speed on land of 30 mph (48.3 kmh).
The dimensions of the vehicle were not to exceed 26’ (7.9 m) long, a beam (width) of not more than 10.5’ (3.2 m), and a deck height of 8.5’ or less (2.6 m). Space was important and the inside of the vehicle had to provide a space of at least 14’ (4.3 m) long and 6’ (1.8 m) wide sufficient for a team of 25 marines with field equipment.
Weight was to be kept at a minimum but not at the expense of armor. The LVTPX-12 was to be an amphibious assault vehicle, so the gunner had to have an efficient view, and the protection had to be enough against 99% of 105 mm air burst shrapnel at 50 feet (15.2 m). Armament was to consist of either a 20 mm cannon or 7.62 mm machine gun mounted in a turret. The US Marine Corps followed this 1964 requirement with their own in March of that year for a new Landing Vehicle Tracked (LVT) to replace their LVTP-5’s.
Several ideas for construction were entertained, and the firm of Chrysler was one of them, and was awarded contract number 4777 for their work. Engineers at Chrysler looked afresh at all areas of amphibian vehicle design with work on the project divided into several phases, with Phase 1 running from June 1964 to May 1965. Three specific area required attention for the design: water speed, armor protection, and the transmission.
Various options for a layout with a single engine were considered including:
Single engine and transmission forward
Single engine and transmission aft
Single engine forward, transmission aft
Single engine aft, transmission forward
Double engines anywhere along the length
Although, in theory, the troops could be unloaded through a front opening door, this exposed them to enemy fire, and consequently the choice, following advice from the US Marine Corps, was an engine and transmission forward design allowing the crew to disembark via a power ramp at the rear covered by fire from the vehicle.
A double or dual engine design permitted more flexibility, being able to put the engines anywhere in the vehicle making the trim much easier to manage. The only engine narrow enough to fit was the GM6-71T but each one produced less power than a 12V71T, just 460 hp. A pair of GM6-71T’s though would produce 800 hp which was plenty, but came at a higher price as together they were heavier and were not as efficient.
The only advantage of the dual engines therefore was an ease of control and with that, the idea was dumped. When consideration was given to transmissions, either Mechanical, Hydrostatic, or Electric, only two engines were under consideration: the 12V71T or the 8V71T.
More than 100 separate models of various types and modifications of the design were produced over the course of testing, including models of just the bow and stern respectively to find the optimum shape. A single box shaped model was made of a 5 road wheel layout to which various shaped box and stern sections could be attached for trials. All these various designs meant that the length and exact water-trim level varied each time. Only the width, at 10.3’ (3.14m) remained the same, although the trials were conducted with a ⅕ scale wooden model rather than a full size pickup. Some of the trials also involved a beam reduction of 20% with a much thinner vehicle to see if that would deliver the water speed improvements demanded. The narrow design caused a lot of problems, the wheels had to have very little travel, just 9” (229mm), and the whole wheel and suspension arrangement was much more complex. This also made handling harder and less efficient. There was insufficient width for two propellers, so only a single propeller could be used, which would mean a loss of ground clearance too. The marginal improvements in performance in the water were not worth the compromises required and the idea was dropped.
Testing of the models was conducted at the Ship Hydrodynamics Laboratory at the University of Michigan, and involved not just the various LVTPX-12 configurations, but also the LVTPX-11, LVTPX-2 and LVTPX-7. The model tests showed that very small scale models gave unreliable results and no model smaller than ⅕ scale should be used for testing. They did however, confirm the final hull shape required and the most efficient method of propulsion in water.
Two options for propulsion of the LVTPX-12 were considered; propulsion in water by the tracks alone, and propulsion by other means, such as bow or stern propellers. Additional consideration was given to the use of hydrojets too.
For the tracks driving the vehicle in water, 5 different types of grousers ranging from 1.12” (28.5 mm) to 1.25” (31.8 mm) wide were tested to find the most efficient type.
The grouser tests showed that increasing the height of the grouser without increasing the width did not increase the efficiency of the vehicle in water, as it simply increased the friction instead. Wider grousers, likewise, did not improve performance either, although grouser number one was marginally better than all of the others. It was also found that, just like with the LVTP-5, the space between the hull and return portion of the track had to be as small as possible and blocked or the returning track would rob the forward track of motive power as it was effectively driving the vehicle in the opposite direction. An attempt of the LVTPX12 model to alleviate this with a completely covered side track made the problem even worse; large side plates did not help and neither did cutting holes in them. If a fender was to be used it would have to be small and only on the forward portion of the track and were essential to meet the design speeds wanted.
Precisely the opposite was true using the propellers to drive the vehicle. Even these small front fenders were harmful to water speed. Therefore, the LVTPX-12 would either be a track driven short-front fender design or a non-fendered propeller driven machine.
One peculiar finding was the use of a stern plane. Contrary to a first impression, the addition of a large flat stern plane placed flat along the back of the tracks, full width, actually improved performance in the water even though it actually interrupted the flow of water. The engineers at Chrysler did not know why this was but found that this had first been suggested in 1860 by Arthur Rigg in Great Britain to improve the efficiency of paddle wheels on ships.
Having looked at the stern plane, the engineers looked at bow vanes and the first attempt involved a design copying that on the LVTP-7. This plane was supposed to prevent submergence of the LVTP-7 at speeds of up to 10 mph, although even in a calm sea the real vehicle struggled to manage 7mph without serious swamping and even less in Sea-State 2 (2 foot waves). The same bow vane fitted toot the LVTPX-12 did not improve performance in the water at all and was actually a hinderance based on a loading of 59,000lbs (26.8 tonnes). The outcome was that a bow plane was pointless and the vehicle was simply better served with a boat shaped bow. Stern shape was even simpler. Because the only bow shape acceptable had to be boat shaped it extended the vehicle to the maximum 26’ (7.92 m), the stern shape could not be boat-shaped. Any angle less than 15 degrees was equally bad and the conclusion was simply to make it square to maximize space instead.
On the question of propellers, the single 27” (686 mm) Kort propeller was found to be highly satisfactory for water propulsion, but caused other problems. It had to be fitted as low as possible for maximum propulsive effort, but it reduced the ground clearance to just 16” (406mm), although a secure stowed position for it was provided. The significant advantage of a single propellor was that it could easily be used for steering the LVTPX-12, but during sharp turns increased the risk of capsize. To solve this capsizing issue, the solution was two propellers with one on each side. Although they would be vulnerable to damage as they projected outside of the width of the vehicle, they would not affect the ground clearance and even should both fail the vehicle would use its tracks to manage 6mph. Controllable steering for a twin propeller design would necessitate the use of controllable pitch propellers.
A better form of steering for the LVTPX-12 was by means of electrically driven 7.5” (191 mm) diameter hydrojets fitted within the sponsons of the machine. These small hydrojets extended just 39” (991mm) along the inside of the sponson weighing just 87 lbs (39.5kg) each.
It was recommended, however, that later some kind of reactive steering should be incorporated within the track drive. For the initial recommendation from Chrysler, the choice was to use twin propellers and vary the pitch to steer the machine. This saved weight and space and allowed for 13 hours of water operation at 8mph.
The Final Designs
After all of the development work, there were 5 main possibilities for the LVTPX12 recommended by Chrysler, all with the same basic dimensions, 26’ long by 10.5’ wide by 8.5’ high (7.9m x 3.2 m x 2.6m), and all of which met the requirements from the Navy, although the report from Chrysler was clear that only concepts 1 or 2 were ideal:
The final designs were based upon a final vehicle weight (unladen) of 45,000 lbs (20.4 tonnes) although some of them went as high as 53,670 lbs (24.3 tonnes) and 26 feet (7.9 m) long. Bow fenders would wrap 150 degrees around the front sprockets with the ability to retract for operation on land. The design would have stern baffles with a contravane extending 4” (101.6 mm), also retractable for land use.
Side skirts were also to be added. They improved water speed and it did not matter what they were made of, just so long as they were smooth and extended to the level of the bottom of the hull. The type 3 bow shape with type 1 grouser were also to be used.
Original requirement was 8 mph (12.8 km/h), but the design was calculated to be able to achieve 10.7 mph (17.2 km/h), although testing only went as high as 9.55 mph (15.4 km/h).
The hull was to use a modern generation of high hardness steel developed by Chrysler Defense Engineering providing the ballistic protection required making the vehicle lighter than it would be with an aluminium hull, as it permitted the hull to be semi-monocoque. Consideration had been given to a dual-hardness steel hull, but although this could save 1090 lbs (494 kg) in weight, the costs involved were considered too high to be justifiable. The same went for the idea of using titanium or ceramics within the armor; the costs simply did not justify the small additional benefits.
The top of the hull, including the cargo hatch, was to be made from military-grade steel (MIL-S-12560), 0.375” (9.5mm) thick with a nylon blanket backing. The sides, front and stern were made from BHN-500 steel, 0.31” (8mm) thick, and the bottom from military-grade steel (MIL-S-12560) too, 0.375” (9.5mm) thick, with structural elements made from either US Steel’s T1 high strength alloy or Cor-Ten low alloy steel as they were far more resistant to corrosion. The flooring inside the vehicle was to be aluminium paneling as were the fenders and external baffles
Protection had been required to defend against shell fragments and small arms fire only, and the use of a steel hull met these requirements. As for armament, Chrysler exceeded the requirements for either a 20mm or a machine gun by adding both. The 20mm Hispano-Suiza cannon and machine-gun were to be mounted coaxially, forwards on the hull in a small 360º rotating turret with 12º of depression. Just 325 rounds of ammunition for the cannon could be carried, but, along with 700 rounds for the 7.62mm machine-gun, provided adequate firepower for the vehicle. Spent casings from the cannon were ejected overboard via an ejection port, but spent cases from the machine-gun were simply to be collected internally. Additional firepower could be given by the mounted troops for whom small arms ports were provided.
During trials, the multiple small wheels had been shown to have far too little travel, so the vehicle to be built was to have 6 large rubber-tyred road wheels on each side instead. These were supported on torsilastic springs cantilevered out from the sides of the vehicle. Drive was delivered to the sprockets at the back, pulling the rubber padded single pin track. The front idler was compensated to account for track movement during amphibious driving and was used to tension the track too.
The transmission for the LVTPX-12 design was a complex problem. The engine would have to deliver in excess of 600h p (recommended to be 800 hp) through the tracks to power the vehicle, which would still only deliver a top speed of 16 mph (25.7 km/h) on land. Various solutions over different types of transmission were considered, all of which were going to be more suitable than using the transmission from a tank like the LVTP-5 had done.
Chrysler concluded that for the final design a new transmission should be developed by a Phase II contractor of a type recommended by Chrysler. Chrysler were prepared to develop this new transmission but not out of their funds. They were clear it would have to be a government-funded and owned project only.
The vehicle itself was to feature just three crew members. A driver positioned in the front left, an assistant driver in the front right and the commander acting as the gunner stood who centrally with his head in the small turret at the front. Seating at the back was provided for 25 troops on benches, although, had the LVTPX-12 been accepted for service, it is likely this area would have been adapted for a variety of other uses too from mortar carrier to recovery vehicle all on the same platform. Access for personnel was via either the large cargo hatch above the troop compartment, the large rear powered ramp, or crew hatches. Two hatches were at the front, with one each for the driver and co-driver, and there were two emergency escape hatches in the vehicle with one on each side of the hull.
Chrysler’s model LVTPX-12 development team had been tasked with producing an amphibian vehicle capable of 8 mph and yet was calculated to be able to manage over 10 mph. In all areas, this design surpassed the LVTP-5, providing for improved armament and performance. The problems of making an amphibian APC were obvious during the development. A large amphibian was simply ill suited to both land and sea operations. Either too heavy for the sea or ill protected for the land. Big, bulky and cumbersome, these vehicles, packed with troops, were to be the amphibious assault vehicles for the US Marine Corps. In comparison with the LVTP5-A1, the LVTPX12 was considered by Chrysler to be a better design and still manageable within the budget constraints imposed by the military.
The US military continued with development of the amphibian as fighting in Vietnam had shown the extreme vulnerability of these vehicles to mines in particular and the requirements of 1964 had changed from high speed beach assault to more emphasis on land operations. The LVTPX-12 design was therefore modified to a more modest vehicle and subsequently the LVTPX-12 was manufactured as a prototype first in September 1967 and later as a batch of 14 more prototypes by Food Machinery Corporation (FMC), which were finished by 1969. It was still the ‘Landing Vehicle Tracked LVTPX-12’, but not for long.
The engine and transmission had been relocated and it was only an LVTPX-12 in name. At least three prototypes and possibly as many as 10 were manufactured under the LVTPX-12 name, but are easily mistaken for the LVTP-7, as the design was modified in favor of a smaller size and weight and refined further. The finished vehicles were smaller, but the work on the original LVTPX-12 was not wasted. It produced valuable experience and lessons for the military.
One prototype vehicle which underwent tests around June 1969 was reported as being made from aluminium instead of steel as originally planned. This switch to aluminium is also confirmed by Hunnicutt, who states that the LVTPX-12s made for trials were made from 5083 aluminium, just like the M113 APC. The Chrysler prefered engine was changed for the smaller 8V53T diesel producing just 400 hp and the torsilastic suspension was changed to torsion bars.
The LVTPX-12 program might not have been successful in itself, but it continued into what was to become the LVTP-7 program instead. By this time, very little of the original form of the LVTPX-12 remained. Gone were the boat shaped front, the central front turret, and side egress doors, and the visual similarities with the LVTP-7 make identification and tracking of the vehicle from this point almost impossible.
Following successful trials of the LVTPX-12 at Aberdeen (Maryland), Yuma Proving Grounds (Arizona), Fort Greely (Alaska), and in Panama it was accepted for service, and the LVTPX-12 name was almost completely dead by 1969, when it was officially redesignated LVTP-7 in this new form and it entered service with the US Marine Corps in 1972, replacing the LVTP-5 completely by 1974.
The fate of these prototypes is not known, although two did get modified into test beds of the LVTRX-2 recovery vehicle with a 30,000 lb (13.6 tonne) winch fitted to the vehicle roof. The weapons cupola was removed at that point. Other experiments were the LVTCX-2 as a Command Variant and LVTEX-3 as an Engineering variant. A final variant planned but never built was the LVTHX-5 with a turret mounted 105mm gun, but all of these had little to do with the original LVTPX-12 and were now firmly in the realm of the LVTP-7.
Strangely, although the LVTPX-12 was ‘dead’ by 1969, the name crops back up again in 1982 with Congress allocating money to design and construct 2 sets of hydropneumatic suspension units for the LVTPX-12 along with clear armor inserts, suggesting the vehicle was still serving, performing a continuing role for testing and evaluation.
At least one of the original prototype vehicles survives at the Allegheny Arms and Armor Museum, Pennsylvania.
Illustration of the Assault Amphibian Personnel Carrier LVTPX-12 produced by Jarosław Janas, funded by our Patreon Campaign.
Specifications LVTPX-12 Track-Propelled Version
26 x 10.6 x 8.6 feet (7.9 x 3.2 x 2.6 meters)
Total weight, battle ready
51,990lb (23.6 tonnes, combat laden) with 10,000lb (4.5 tonnes) payload
1 x 1 x .50 cal. (12.7 mm) Browning M2 Heavy machine gun
Welded 5083 aluminium
Final Engineering Report on the LVTPX12, Vol.1 Technical Study. (1965 ). Chrysler Corporation, Detroit.
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.
The Stability of the amphibious Craft LVTPX-12 in Waves and Surf. (1968). Robert Patterson. Massachusetts Institute of Technology, Department of Naval Architecture.
Evaluation of LVA Full-Scale Hydrodynamic Vehicle Motion Effects on Personnel Performance. (1979). William Stinson. Naval Personnel Research and Development Center.
Bureau of Ships Preliminary Specification for Assault Amphibian Personnel Carrier (LVTPX12), (1964). Bureau of Ships
US Marine Corps FY82 Exploratory Development Program. (1982). Marine corps Development and Education Command
LVTPX-12 Accepted. (November 1967). J.H. Alexander. Marine Corps Gazette Vol. 51, Issue 11
Special Test for LVTPX-12. (June 1969). Marine corps Gazette Vol.53, Issue 6. Amtracs: US Amphibious Assault Vehicles. (1999). Steven Zaloga, Terry Handler, Mike Badrocke. Osprey New Vanguard No.30 Bradley: A history of American fighting and support vehicles. (1999) R.P. Hunnicutt, Presidio Press
Self-Propelled Gun (SPG) – 1 Prototype
During the mid-1970s, the US Military determined that there was a need to update, replace or overhaul their existing and aging fleet of self-propelled guns (SPG). The focus was on the replacement of the M109 SPG and several options were available. The US Army could select a foreign vehicle such as the French GCT, or the Italian/UK/German SP-70 project, or a new project could be started. The military, unsurprisingly, selected a US-based program and had to consider whether to replace the whole fleet with a common chassis fulfilling roles of command, resupply, and repair or instead, just modernize/upgrade the existing fleet.
Amongst the replacement vehicles considered, the proposal made by Food Machinery Corporation (FMC) under the name DSWS New Start (DSWS – Division Support Weapon System) was rejected by 1983. The emphasis instead of replacement was going to be upgrade and modernization. FMC had invested a considerable amount of time and financial resources into their design and would try to reuse this development in an M109 rework. This was to be the M109 Maxi-PIP (Product Improvement Program)
The existing US SPG fleet was a mix of vehicles, calibers, and ages. There was no simple common Ammunition Resupply Vehicle (ARV) either, and a common vehicle platform for both an artillery system and its resupply vehicles would have obvious advantages for parts, supplies, logistics, and training. The work on FMC’s own platform for all of this had been discontinued already though.
The rate of fire for existing in-service SPG’s was also too slow, of the order of just 4 rounds per minute manually loaded. The US Army wanted to improve on this and an automatic loader would achieve this with up to 12 rounds per minute being possible. Another problem was that the crews of existing SPGs were too large, which lead to logistical problems such as training and maintaining these soldiers in the field. An automatic loader and automatic subsystems would help reduce this human burden.
In particular, the existing engine of the M109 was considered underpowered for its role. An improved power-to-weight ratio of 20 horsepower per ton was set for the upgrade project along with improved reliability. The M109 was a product of the 1950s and simply did not reflect the realities of modern warfare. It was vulnerable to counter-battery fire from Soviet artillery as it took too long to stop, fire, and then move on. Modernized fire control systems, gun elevation motors, and ground mapping would allow the improved vehicle to fire, move, and fire again to reduce successful enemy retaliation. Finally, the old M109 just did not have the range needed to counter fire the Soviets, which was a huge tactical weakness. These requirements formed the basic needs of the Howitzer Improvement Program (HIP).
Howitzer Improvement Program
The 155 mm gun caliber would remain, but the barrel had to be between 38 calibers (5.89m) and 50 calibers (7.75m) long. It had to be able to fire all current and future 155 mm rounds and have a range of 25 to 30 km when using High Explosive Rocket Assisted (HERA) ammunition. Either a fully or semi-automatic loading system was needed to increase the rate of fire and reduce the number of crewmen. New electronics were also needed to enable a 1-minute fire-move-and-fire-again cycle, along with a facility to fire a 3 round burst in 10 seconds. Increased ammunition capacity of at least 50 shells was also demanded.
FMC M109 Modification Proposal
When the original FMC DSWS project was canceled, FMC had luckily also submitted a proposal to update the existing M109 fleet. It was as an alternative to their own proposal for a completely new vehicle with the 155 mm L/45 gun. The upgrade/update idea though was to combine the old M109’s with some of the elements from the completely new vehicle proposal.
This would include the new suite of electronics which would improve accuracy from the same 155 mm L/45 gun but the most obvious and important change would be the switch to an automatic loading system. Fed from two large drums in the back of the turret, the 155 mm shells would be replenished by means of two circular hatches at the bottom of each door. Both doors could also be opened to allow for complete inspection or repair of the drums. The autoloader would also decrease the crew for the vehicle by eliminating the need for one of the loaders.
This upgraded M109 would be marketed under the name M109 Maxi-PIP (Product Improvement Program) and had the advantage of retaining the turret (albeit modified) of the M109. A wooden mockup was shown to the military and received sufficient interest to have a single test chassis produced based on an M109. This prototype weighed in at just over 29 tonnes.
The M109 Maxi-PIP was still under development in 1982 with an existing M109 chassis modified to simulate the new 29-ton (26.3 tonnes) vehicle weight. The engine fitted was a 500 hp Detroit-Diesel 8V71TA and was subjected to the NATO 400 hour engine test. Tests were still scheduled to take place with this engine into 1983. Various other types of engines were considered but 500hp in a 29-ton (26.3 tonnes) vehicle would only produce 17 hp/t which was not the required 20hp/t wanted, therefore this new vehicle was not able to provide the required mobility improvements.
The M109 PIP from FMC faded away and was completely canceled by 1984 with the decision being made at the time to simply modify the M109 fleet with new ammunition stowage and a longer range gun. Pacific Car and Foundry (PCF) had also made its own proposal to fulfill the requirements for the future artillery system under the name ‘Self Propelled Artillery Weapon’ (SPAW). The PCF proposal was also a fully automatically loaded gun system but was capable of firing unassisted shells to a range of 30km and to 40km with a rocket-assisted projectile. The SPAW would have had a crew between 2 and 4 and with an engine providing a power to weight ratio of between 20 to 25 hp/t and could move at up to 40km/h off-road. Neither project could meet the Army’s needs and, as a result of the failure to develop or accept a replacement, the existing M109’s soldiered on.
As with many of these multi-year huge contracts in the US, this one is an enormous project of overlapping requirements. The HIP program did not end with FMC or PCF concepts though and was still going on into 1991. This was the date by which the vehicles for the program were meant to have been entering service yet development hadn’t even finished and only 8 prototype improved vehicles for the entire program had even been made by 1989.
The project was simply too large and phenomenally expensive. In 1989 alone, for example, the HIP program cost nearly US$28.5 million and nearly US$10.5 million the following year. It didn’t matter anyway for FMC. Their initial proposal had been rejected, as was their M109 improvement. The project was somewhat of a failure, no new vehicle was produced and a huge amount of financial resources was spent. The opportunity for a new and more capable platform producing a new family of vehicles was lost. The PIP had not managed to meet the needs for a future artillery system and the US finished out the 1980’s behind the Soviets in terms of self-propelled artillery, unable to select or develop a suitable M109 replacement.
Illustration of the M109 Maxi-PIP produced by Pavel Alexe, funded by our Patreon Campaign.
155 L45 main gun, one cupola mounted .50 cal heavy machine gun
50 rounds in two 25 round drums with fully automatic feed capable of firing unassisted projectiles to 23km
GAO Report AD-A141 422 M109 to M109A5 Report, March 26th 1984
Janes Armour and Artillery 1984-5
US Army Tank Automotive Command Laboratory Posture Report FY 1982, US Army
Research Development and Evaluation Army Appropriation descriptive summaries, January 1990, US Army Congressional Report
Report ARLCD-CR-81053, Demonstration Prototype Automated Ammunition and Handling System for 155mm Self-Propelled Howitzer Test Bed, December 1981, US Army ARRADCOM
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