Categories
Cold War Canadian prototypes Coldwar American Prototypes

‘Cobra’ Light Cross Country Combat Vehicle (Cobra LCCCV)

USA/Canada (1950-51)
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.

Overall Design

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.

Comparison of standard track to the new spaced link type track. Source: Modified from Army Service Technical Information Agency Working Paper ATI 149375, 1951

Automotive

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.

Comparison between existing 140hp 6 cylinder 4-stroke Hercules unit and the desired 180hp 18 cylinder 2 stroke multi-bank engine. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

Armament

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.

American T124 76mm Anti-Tank gun. Photo: Lovett Artillery Collection

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.

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Hit probability based on the three types of ranging. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951
Salvo based hit probability for the M27 recoilless rifle. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

Armor

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.

Configurations

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.

Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951
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Cobra AC-1 Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

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.

Cobra AC-2 Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

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.

Cobra AC-3 Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

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.

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Cobra CC-1. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951
CC-2. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

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.

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Four other drawn variants on the articulated platform Cobra. Mortar, AA, Rocket launcher and Cargo versions. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

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.

Conclusions

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

Sources

Army Service Technical Information Agency. (1951). Working Paper ATI 149375: Analysis of a Light Cross Country Combat Vehicle ‘The Cobra’.
Lovett Artillery Collection
US Army Materiel Command. (1976). Engineering Design Handbook: Recoilless Rifle Weapon Systems.
US Army (1951). TM9-329 105mm Rifle M27, 105mm Rifle Carriages M22 and T47 Modified and 105mm Rifle Mounts M75 and T143.
US Army. (1952). T/O&E 7-15 M27 105mm Recoilless Rifle
Rayle, R. (2006). Random Shots: Episodes in the Life of a Weapons Developer. Merriam Press


Categories
Coldwar American Prototypes

Assault Amphibian Personnel Carrier LVTPX-12

U.S.A. (1964 – 1982)
Landing Vehicle Tracked (LVT) – 15 Built

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.

Planning

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
Ramp forward concept for the LVTPX-12, which was quickly abandoned. Source: Chrysler Corporation

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.

Diagrammatic of the twin-engine LVTPX-12 proposal. Source: Chrysler Corporation

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.

Table showing the different equipment systems that were under consideration.

Modelling

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.

Side and cross sectional views of the narrow LVTPX-12 concept. 20 % narrower than the standard vehicle. Source: Chrysler Corporation
Partial model made for water testing lacking stern and bow. Source: Chrysler Corporation

Testing

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.

Water Propulsion

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.

Large flat sern plane. Source: Chrysler Corporation

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.

Rear view of LVTP12 designs with single 27” (686mm) Kort propeller. 26” (660mm) versions were also tested. Source: Chrysler Corporation
Double 29” (737mm) Kort propellers in the open and stowed positions seen from the rear. Source: Chrysler Corporation

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.

LVTPX-12 with the rear ramp and hydrojet positions at the bottom of the hull. Space for 26 men and three crew provided. Source: Chrysler Corporation

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.

Positions of one of the auxiliary drive units. Source: Chrysler Corporation

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:

  • Concept 1: Track Propelled, 12V71T engine
  • Concept 2: Auxiliary Propelled, 12V71T engine
  • Concept 3: Auxiliary Propelled, 8V53T engine
  • Concept 4: Auxiliary Propelled, 8V71T engine
  • Concept 5: Auxiliary Propelled, twin AC-350C engine

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).

Final hull profile of the LVTPX12. Source: Chrysler Corporation

Protection

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.

Structural framework for the LVTPX12. Source: Chrysler Corporation

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.

LVTPX-12 ‘Track Propelled’ version. Source: Chrysler Corporation
LVTPX-12 ‘Screw [Propeller] Propelled’ Version. Source: Chrysler Corporation

Suspension

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.

Transmission

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.

Artist’s conception of the LVTPX12. Source Hunnicutt

Crew

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.

LVTPX-12 model completed 1967 in an early form with boat-shaped front, which was later abandoned.

Outcomes

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.

LVTPX-12 possible prototype hull No.1 during trials. The ‘guns’ appear to be dummies with the cannon below the machine gun rather than coaxial. The lines are clean and smooth but the front has lost its boat shape. Photo: snafu-solomon.com

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.

LVTPX-12 3rd prototype seen during trials about 1970. Very little of the original LVTPX-12 remains. Source: US Marine corps

Epilogue

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.

Planned but never built LVTPX-12 based LVTHX-5 with turret-mounted 105mm gun. Source: Hunnicutt

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.

LVTPX-12 10th Prototype during trials with the 4th Marine Division at Camp Pendleton (California) in about 1971. One of two prototypes was received there for familiarisation training. Source: USMC and Hunnicutt

At least one of the original prototype vehicles survives at the Allegheny Arms and Armor Museum, Pennsylvania.

Surviving LVTPX-12 prototype number 12. Source: Harold Biondo


Illustration of the Assault Amphibian Personnel Carrier LVTPX-12 produced by Jarosław Janas, funded by our Patreon Campaign.

Specifications LVTPX-12 Track-Propelled Version

Dimensions (L-w-H) 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
Crew 3 (Driver, Assistant Driver, Commander) + 25 troops
Propulsion GM 12V71T 800hp
Maximum speed > 10 mph (16.1 km/h) in water, 30 mph (48.3 km/h) on land. < 5 mph (8 km/h) in reverse in water
Armament 1 x 20mm Hispano Suiza cannon and 1 x 7.62mm machine-gun
Armor Welded steel up to 8mm thick

Specifications LVTPX-12 Auxiliary-Propelled Version

Dimensions (L-w-H) 26 x 10.6 x 8.6 feet (7.9 x 3.2 x 2.6 meters)
Total weight, battle ready 53,670lb (24.3 tonnes, combat laden) with 10,000lb (4.5 tonnes) payload
Crew 3 (Driver, Assistant Driver, Commander) + 25 troops
Propulsion GM 12V71T 800hp, 8V53T 400hp, or 8V71T 530hp
Maximum speed > 10 mph (16.1 km/h) in water, 30 mph (48.3 km/h) on land. < 5 mph (8 km/h) in reverse in water
Armament 1 x 20mm Hispano Suiza cannon and 1 x 7.62mm machine-gun
Armor Welded steel up to 8mm thick

Specifications LVTPX-12 (LVTP-7) Prototype

Dimensions (L-w-H) 26 x 10.6 x 8.6 feet (7.9 x 3.2 x 2.6 meters)
Total weight, battle ready 48,500 lbs (22 tonnes)
Crew 3 (Driver, Assistant Driver, Commander) + 24 troops
Propulsion GM 8V53T 400hp diesel
Maximum speed 40mph (64.3 km/h) land 8.4mph (13.5 km/h) water
Armament 1 x 1 x .50 cal. (12.7 mm) Browning M2 Heavy machine gun
Armor Welded 5083 aluminium

Sources

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


Categories
Coldwar American Prototypes

M109 Maxi-PIP Howitzer Improvement Program

USA (1979-1984)
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)

Artist’s impression of the FMC M109 Maxi-PIP project. Source: Janes

The Flaws

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.

Artist’s impression of the FMC M109 Maxi-PIP project. Source: Janes
The mock-up vehicle on display. Source: Ed Francis
Rearview of the same mockup showing the resupply doors open. Source: Ed Francis

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.

M109 Maxi-PIP weighed mockup. Source: US Army

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.

Conclusion

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.

Artist’s impression of the ammunition stowage and loading system on the Maxi-PIP. Source: Richard Eshleman

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.

Specifications

Armament 155 L45 main gun, one cupola mounted .50 cal heavy machine gun
Ammunition 50 rounds in two 25 round drums with fully automatic feed capable of firing unassisted projectiles to 23km

Sources

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


Categories
Coldwar American Prototypes

Cargo Carrier M548 with Surface-Launched Unit, Fuel Air Explosive (SLUFAE)

U.S.A. (Mid-1970s)
Mine Clearing Vehicle

Minefields are, quite rightly, well feared by troops and commanders alike. Hidden, silent killers, these weapons can lie dormant for years and cripple men and machines alike. With the Cold War stand-off between NATO and the Warsaw Pact in full flow, both sides planned to make extensive use of minefields to disrupt enemy movements and attacks. The side with the fastest and most efficient means of clearing a path through an enemy’s minefield would obviously have a significant advantage in a war.
Early research work with turning Fuel Air Explosive (FAE) technology into weapons was undertaken by the US Navy in the early 1960s at their China Lake Naval Weapons Center in California. By the mid-1970s, research had progressed sufficiently to weaponize FAE technology into two primary weapons systems: one ground-launched which was developed in conjunction with the US Army Missile Command (MICOM), the ‘Surface Launched Unit’ (SLU-FAE); and one delivered by air, the CBU-55/72. The design was completed by 1975, and prototype firings ready that year for testing the SLUFAE for its intended primary role, defeating enemy minefields. This evaluation was done in conjunction with the US Army Mobility Equipment Research and Development Center (MRDC) at Fort Belvoir, Virginia.

The ‘Surface-Launched Unit, Fuel Air Explosive’ or ‘SLUFAE’ mounted on the M548. This photo shows the arrangement of the tubes in the POD. Photo: US Army

The SLUFAE System

The SLUFAE system consisted of a single giant octagonal ‘pod’ containing 30 smooth walled 35cm diameter tubes, although the original artwork for the program had shown 36 tubes in a rectangular pod and then confusingly described it as a ‘30-tube’ system. These barrels were able to the fired individually or ripple fired at intervals variable from 1.0 seconds to 9.7 seconds in 1/10 second intervals. The whole system could throw all 30 rockets in sequence which was capable of breaching an 8m wide path 900m long. The minimum safe detonation distance was 100m so the carrier could park as close as 100m from the edge of the minefield and launch the rockets.

Uncamouflaged SLUFAE during test firing. The very large size of the rocket is apparent. Photo: US Army
The whole pod was to be mounted on a ground vehicle and the vehicle selected was the M548 Tracked Cargo Carrier vehicle, although it has also been described as being based on the M752 Lance Missile Carrier which was being decommissioned as a platform at the time.
Stowed horizontally on the back of the M548, the POD stuck up well above the vehicle line and could be elevated up to a maximum of 30 degrees when the POD was to be deployed.

SLUFAE rocket launched from the camouflaged POD on the M458. Use of such a system was liable to draw a lot of enemy attention. Photo: Zaloga via US Army

Rear of the SLUFAE showing the use of the POD mounted crane arm for reloading these large rockets. Photo: Yuri Pasholok

The rocket

The XM130 SLUFAE (also sometimes written as ‘SLU-FAE’, was a 2.55 m long, 345 mm diameter, 84.8 kg unguided rocket fitted with an XM750 Slowed Nose Probe (discriminating against the effects of foliage) and Mild Detonating Fuze. Propelled by a 5” (127 mm) ‘Zuni’ rocket motor inside the launching tube body, this would propel it from the vehicle-mounted tube out to a maximum range of 1000 m, although 700m was deemed to be the effective limit.

Preserved SLUFAE rocket (center, dark green) at the Hawthorne Ordnance Museum, Nevada. Photo: Courtesy of the Hawthorne Ordnance Museum
Once over the target, the rocket was retarded by a parachute in the tail shroud and the main charge, consisting of 45 kg of Propylene Oxide (PO) explosive liquid, was burst over the target forming a cloud 12’ x 54’ (3.7 m x 16.5 m) which was then ignited (150/1000 second delay) causing a huge explosion and overpressure on the target which would subsequently detonate any mines. An inert version for training use was designated XM131. Accuracy for this unguided system was poor though. with a dispersal of 2.6 m laterally and 6 m in range for every 300 m traveled, meaning a maximum deflection of 8.6 m laterally and 20 m in range leaving a chance that at the end of the lane of cleared mines that some mines may not have been covered by the overpressure.

Diagrammatic break down of the XM-130 SLUFAE rocket showing the large payload (8), burster charge (9) at the front and the Zuni rocket tube (3) behind. The retarding parachute is marked at (5). Photo: Dept. of Defense


The Cargo Carrier M548 fitted with the large Surface-Launched Unit, Fuel Air Explosive (SLUFAE) launcher fitted to the rear of the vehicle. Illustration by Andrei ‘Octo10’ Kirushkin, funded by our Patreon Campaign.

Testing

Testing of the SLUFAE on the M548 took place in 1975, with further tests throughout 1976 and 1977. Consideration was given to the effectiveness of ground-pressure detonation of mines, including tests of the FAE system (although not SLUFAE rockets) on frozen ground in Alaska, which provided concern over their effectiveness, particularly against frozen or partially frozen soils. By 1981, further studies were recommended into the performance degradation of this type of system in cold temperatures and against the frozen or thawing ground.

Montage showing demonstration of SLUFAE rocket against a target building at China Lake and alternative deployment of FAE device by helicopter. Photo: British Ordnance Collectors Network
The overpressure effects on vehicles and troops were devastating. Trucks were crushed by the overpressure and exposed troops would be killed or seriously injured. Light structures such as houses were seriously damaged, but the effect was very small against armored targets. The primary intended use had been seen in using overpressure against landmines causing them to detonate and under normal temperate conditions, it had worked. The use of FAE had even worked for underwater mines, making it suitable for use in clearing mines laid below the water line on a beach, but the carrier was unprotected and the whole system was huge.

Demonstrated effect of FAE explosives in 1975 showing a 2 ½ ton standard US Army truck completely crushed by the overpressure blast which also set it on fire and blew off major parts. Photo: US Army

Future Developments

The SLUFAE system was eventually not adopted for use. In the 1998 patent for an improved version of FAE mine clearance, a description of the SLUFAE rockets put the maximum range to just 700 m and that to ensure mines are destroyed a lot of overlap was required to destroy single impulse mines or ones buried in excess of 15cm deep. As a result, the clearance area from 30 rockets was just 8 m by 160 m, substantially less than the 700-1000 m lane originally intended. This is likely the key reason the system was not adopted. It just was not reliable enough. Systems such as ‘Giant Viper’ were more effective and provided a cleared lane through a minefield by virtue of the 183 m long hose filled with PE6/A1 High Explosive. That system was much simpler logistically as it was carried in a trailer and could be brought to a designated area by almost any vehicle rather than relying upon a dedicated and much bigger tracked carrier.
The SLUFAE was a good idea but was unsuitable for actual combat. The USMC, who was particularly interested in amphibious assault vehicles, looked at the Army’s SLUFAE for their own use in 1987. They concluded that “this system is not compatible with Marine Corps amphibious assault and tactical vehicles, does not provide a breaching capability starting at the high watermark, and does not meet the Marine Corps stated requirements”.
The development of SLUFAE had been quick in military terms, completing development and being officially accepted in December 1980 (FY 1981). It had been pursued, however without sufficient testing under different terrain conditions and the tactical disadvantages of this large, vulnerable and conspicuous machine were readily obvious. It was duly shelved and received no procurement orders.

Conclusion

By the 1990’s, FAE technology had continued with the addition of aluminum particles to increase the overpressure from the blast, but the SLUFAE rockets were gone. Nothing is known about the location of the SLUFAE launcher, but at least two rockets survive. One in a private collection and one in the collection of the Hawthorne Ordnance Museum in Nevada.

Minefield clearance with FAE from Patent US4967636A preparing the route for a tank. Photo: US Patent US4967636A
The original design had morphed to consider the use of a flexible hose containing FAE launched in a manner similar to that of the ‘Giant Viper’ system. Instead of exploding in the air, this version of the SLUFAE system would explode on the ground instead. The means of destruction was the same though – the creation of a pressure wave to detonate the mines. The system was never adopted though and production of the SLUFAE was limited to a single prototype.

Sources

Osprey Publishing, New Vanguard #252: M113 APC 1960-75, Steven Zaloga
Special Report 81-20, Mine/Countermine Problems during Winter Warfare, Virgil Lunardini, September 1981
NAWCWD Quick Facts, China Lake and Point Mugu, California, March 2008
Department of Defense Military Handbook – Fuzes, April 1994
William Stirrat, US Army Armament Research and Development Center Large Calibre Weapon Systems Laboratory, Minimum nonpropagation distance for the cloud detonator of the XM130 SLUFAE rocket, February 1984
Infantry Magazine Vol.66, US Army, March-April 1976
Jai Agrawek, High Energy Materials: Propellants, Explosives and Pyrotechnics.
James Dennis, MERDC Demonstrates Fuel Air Explosive Mine Neutralization Capabilities, US Army Research and Development Bulletin January-February 1975
US Patent US4967636A filed 23rd September 1988
Canadian Patent CA2197508, Land Mine Destroying and Disabling System, 13th August 1998 and 30th November 1999
Required Operational Capability for Amphibious Continuous Breach and Land Mine Countermeasure System. Department of the Navy, 1987
Remote Controlled Vehicle Mounted Minefield Detector System, US Army Mobility Equipment Research and Development Command. November 1982
US Army Mobility Equipment Research and Development Plan, March 1981
FY 1982 Department of Defense Program for Research Development and Acquisition

Categories
Coldwar American Prototypes

120mm Gun Tank T57

U.S.A. (1951)
Heavy Tank Prototype – 2 Turrets Built

The T57 started life in the early 1950s. At this time, the 120mm Gun Tank T43 (which would become the M103) was well on its way to becoming America’s next heavy tank, but even before it had entered serialization, ideas began to circulate about future upgrades.
One such idea was the possibility of mounting an auto-loading device in the tank’s turret, and further study into this idea proved that such a device would be ill-suited to the T43’s turret. As such, concentration turned to a new turret design, which would be mounted on pivoting trunnions. In other words, designers began to consider the addition of a new technology at the time, an Oscillating Turret. Testing at the Aberdeen Proving Grounds (APG) had already proved that smaller caliber guns worked in such turrets. There was no reason that a larger caliber gun, such as the powerful 120mm, wouldn’t work in such a turret. A development program was initiated on October 12th, 1951, with the project receiving the designation of 120mm Gun Tank T57.

One of the earliest concepts of the T57. Photo: Presidio Press

Development

On 12th October 1951, a development program began to design a 120mm armed heavy tank with an Oscillating turret and automatic loader. Two pilot models were authorized, and the tank was designated as the 120mm Gun Tank T57. The turrets, each with 2.1 meter (85 inch) rings, were to be tested on the hull of the T43. Two hulls of which were earmarked for this purpose.
The initial design for the autoloader was for a cylindrical type mounted directly behind the breach of the gun in the turret bustle. However, it was predicted that the measurements of such a device would take up a space of 76 cm – 1 meter (30 – 42 inches) but this depended on whether the cylinder would hold 11, 9 or 6 rounds. Army Field Forces (AFF) rejected this design, stating that such equipment would end up with the turret bustle being overly large in overall dimensions, as well as in the overhang of the bustle.
To overcome this possible design flaw, a contract was drawn up with the Rheem Manufacturing Company to design and construct the two authorized pilot vehicles.

Another early concept of the T57

Turret

The Oscillating type of turret consists of two actuating parts, these were a collar that is attached to the turret ring, allowing horizontal traverse, and a pivoting upper part that holds the gun, loading mechanism, and crew. Both halves of the T57’s turret were cast in construction, utilizing cast homogeneous armor. Armor around the face was 127mm (5-inches) thick, angled at 60 degrees. The armor on the sides of the turret was slightly thicker at 137mm (5.3 inches) but was only 51 mm (2 inches) on the bustle.
The sides of the collar were bulbous to protect the trunnions that the upper half pivoted on, with the other half consisted of a long cylindrical ‘nose’ and a low profile flat bustle. The turret was mounted on the unmodified 2.1 meter (85 inch) turret ring of the T43 hull.

Cutaway views of the enternal systems and layout of the turret. Photo: Presidio Press
Though it looks as though there were two, there were actually three hatches in the roof of the T57. There was a small hatch on the left for the loader, and atop the commander’s cupola which featured five periscopes and a mount for a .50 Caliber (12.7mm) machine gun. These hatches were placed on top of the third hatch, which was a large square that took up most of the middle of the roof. This large hatch was powered and granted a larger escape route for the crew but also allowed internal turret equipment to be removed easily. In front of the loader’s hatch was a periscope, and there was another above the gunner’s position.
Behind the large hatch was the ejection port for spent cartridges. To the right of this was the armored housing for the ventilator housing. On each side of the turret were ‘frogs eyes’, the armored covers for the stereoscopic rangefinder used to aim the main gun.

Gun

The initial Rheem concept had the gun rigidly mounted without a recoil system in a cast, low silhouette Oscillating turret, with the gun protruding from a long, narrow nose. The gun featured a quick change barrel, which was which was similar to the 120mm Gun T123E1, the gun being trialed on the T43. However, for the T57, it was modified to accept single piece ammunition, unlike the T43 which used separately loading ammo. This new gun was attached to the turret via a conical and tubular adapter that surrounded the breech end of the gun. One end screwed directly into the breach, while the front half extended through the ‘nose’ and was secured in place by a large nut. The force created by the firing of the gun and the projectile traveling down the rifled barrel was resisted by rooting the adapter both the breech block and turret ring. As there was no inertia from recoil to automatically open the horizontally sliding breech block, a hydraulic cylinder triggered by an electric switch was introduced which would be engaged upon the firing of the gun.
This new variant of the T123 was designated the 120mm Gun T179. It was fitted with the same bore evacuator (also known as a fume extractor) and muzzle break as the ‘T123’. The gun’s rigid mount was designated the ‘T169’, making the official nomenclature ‘120mm Gun T179 in Mount T169’
In the oscillating turret, the gun could elevate to a maximum of 15 degrees, and depress 8 degrees. Projected rate of fire was 30 rounds per minute. The main gun had a limited ammunition supply due to the large size of the 1-piece rounds. The T43 hull had to be modified to allow storage, but even then, only 18 rounds could be carried.
It was proposed that two .30 Caliber (7.62mm) machine guns would be mounted coaxially. This was later reduced to a single machine gun placed on the right side of the gun.

Automatic Loader

The automatic loader used on the T57 consisted of a large 8-round cylinder located below the gun, and a ramming arm that actuated between positions relative to the breech and magazine. The loader was designed for 1-piece ammunition but an alternate design was prepared for use with 2-piece ammunition.
Operation: 1) The hydraulically operated ramming arm withdrew a round and aligned it with the breach. 2) The rammer then pushed the round into the breach, triggering it to close. 3) Gun is fired. 4) Effect of gun firing trips the electric switch that opens the breech. 5) Rammer picks up a fresh round, at the same time ejecting the spent cartridge through a trap door in the roof of the turret bustle.

A diagram of the loading process. Photo: Presidio Press
Ammunition types such as High-Explosive (HE), High-Explosive Anti-Tank (HEAT), Armor Piercing (AP), or Armor-Piercing Ballistic-Capped (APBC) could be selected via a control panel by either the Gunner or the Tank Commander (TC). The HEAT round could punch through a maximum of 330mm (13 inches) of Homogeneous Steel Armor.

Hull

The hull that was used for the project was the same as the 120mm Gun Tank T43, which would later be serialized as the M103, the US’ last heavy tank. Armor on the hull was unchanged. The cast “beak” was 100 to 130 mm (3.9-5.1 in) at the thickest.
An 810hp Continental AV1790 12-cylinder air-cooled gasoline engine propelled this chassis to a speed of around 21 mph (34 km/h). The tank’s weight was supported on seven road wheels attached to the torsion bar suspension. The drive sprocket was at the rear while the idler wheel was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. The return of the track was supported by six rollers.

Line drawing of the complete T57, with OScilliating turret mounted on the T43/M103 hull. Photo: Presidio Press

Crew

The T57 had a crew of four men. The Driver’s position was standard for T43/M103 hulls. He was located centrally in the bow at the front of the hull. Arrangements inside the turret were standard for American tanks. The Loader was positioned at the left of the gun. The Gunner was on the right with the Commander behind him.

Fate

The T57 project eventually ground to a halt. Progress became slow due to delays in procuring some equipment from the US Government. This problem was due, in no small part, to changing opinions in tank design. Designers were moving towards lighter vehicles that retained powerful guns, instead of heavy (as in weight and class) tanks.
One of the two pilot turrets constructed by Rheem was trial fitted to a T43 hull. Work on the project, however, stopped before tests of the systems could take place. The United States Ordinance Committee officially canceled the project on January 17th, 1957. Both turrets were subsequently scrapped, and the T43 hulls were returned to a supply depot for future use.
The T57 did, however, live on in another tank project, but this time in the shape of a medium tank. This project was designated the 120mm Gun Tank T77. It was a project to mount the T57’s turret on the hull of the 90mm Gun Tank T48, the prototype of the M48 Patton III. Just one photo, a model, and blueprints exist.
The Rheem Company would also continue to design tank components for the United States Military. Other projects they worked on included the 90mm Gun Tank T69, and 105mm Gun Tank T54E1 projects. Both of which featured similar turrets and loading systems.

A small scale mock-up of the T57. Photo: Presidio Press

TE to the Rescue

In late-2017, a scale model of the T57 produced by Rheem appeared on the internet auction sight, eBay. This model had appeared a number of times on the website without being purchased. The model was made for Fort Benning Armored Force Command. It is made from solid aluminum and weighs nearly 22 pounds (10 kg), it is also 2 feet (70 cm) long.

The scale model of the T57 from when the item was put up for auction on eBay.
Rather than let the model fall into the hands of a private collector, and be hidden from view, the Tank Encyclopedia team decided to step in a secure its fate in partnership with the U.S. Army Armor & Cavalry Collection, Georgia, USA. A fundraiser was organized and launched by Andrew Hills of FWD Publishing – and one of our writers – on the website ‘GoFundMe’ in November 2018. The thinking behind this was that he (all of us) wanted to see the model get to its rightful home – a national collection where it could be enjoyed by future generations and help foster a greater understanding of the evolution of American armour.
By the end of 2018, we had raised the necessary $700 to purchase the model. Just as planned, it was sent to the Museum. It is now safe and sound, reserved for future generations to see.

The T57 model at the U.S. Army Armor & Cavalry Collection. Photo: AACC

An article by Mark Nash

Specifications

Dimensions (L-w-H) 37.4 (including gun) x 8.7 x 9.45 ft (11.32 x 2.6 x 2.88 m)
Total weight, battle ready 48.5 tons (96 000 lbs)
Crew 4 (Commander, Driver, Loader, Gunner)
Propulsion Continental AVDS-1790-5A V12, AC Twin-turbo gas. 810 hp.
Transmission General Motors CD-850-3, 2-Fw/1-Rv speed GB
Maximum speed 30 mph (48 km/h) on road
Suspensions Torsion bars
Armament Main: 120 Gun T179 Sec: 1 Browning M2HB 50. cal (12.7mm), 1 cal.30 (7.62 mm) Browning M1919A4
Production 2

Links & Resources

OCM (Ordnance Comittee Minutes) 34048
April 1954 Report from the Office of the Chief of Ordnance (PDF)
Presidio Press, Firepower: A History of the American Heavy Tank, R. P. Hunicutt


Rendition of the T57 heavy tank in a fictional livery based on common styles from the era. Illustration by Alexe Pavel, based on an illustration by David Bocquelet.

Categories
Coldwar American Prototypes

120mm Gun Tank T77

U.S.A. (1951)
Heavy Tank Prototype – 2 Turrets Built

In October 1951, a heavy tank project was underway to mount an oscillating turret with an automatically loading 120mm Gun on the hull of the 120mm Gun Tank T43. (The T43 would later be serialized as the 120mm Gun Tank M103, America’s last heavy tank.). This was the T57, and the Rheem Manufacturing Company were granted a contract to design and build two pilot turrets and autoloading systems.
During the T57’s development, it became clear that it was feasible to mount a lighter armored version of the T57 turret on the hull of the 90mm Gun Tank T48 (The T48 later became the 90mm Gun Tank M48 Patton III). This combination granted the possibility of creating a ‘heavy gun tank’ that was lighter than any previously designed.
In May 1953, a development project was started to create such a tank. It would be designated the 120mm Gun Tank T77, and another contract was signed with Rheem to create two pilot tanks.

Hull

The hull chosen for the project was that of the 90mm Gun Tank T48. The tank weighed about 50 tons, with armor of up to 110mm thick.
The tank was powered by a 650 hp Continental AVSI-1790-6 V12, air-cooled twin-turbo gasoline engine. This would propel the tank to a speed of 30 mph (48 km/h). The tank was supported on a torsion bar suspension, attached to six road wheels. The drive sprocket was at the rear, while the idler was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. The return of the track was supported by six rollers.

A small scale mockup of the T77. Photo: Presidio Press

Turret

The Oscillating type of turret consists of two actuating parts, consisting of a collar that is attached to the turret ring, allowing horizontal traverse, and a pivoting upper part that holds the gun, loading mechanism and crew. Both halves of the T57’s turret were cast in construction, utilizing cast homogeneous steel armor. Armor around the face was 127mm (5 inches) thick, angled at 60 degrees. This increased to 137mm (5.3 inches) of the sides of the turret and dropped to 51 mm (2 inches) on the bustle.*
*The T77’s turret was supposedly designed to be lighter by having thinner armor, however, Hunnicutt’s data shows it to be the same as the T57’s turret. Whether this is erroneous or not is unknown.
The sides of the collar were made to be round and bulbous in shape to protect the trunnions that the upper half pivoted on. The other half consisted of a long cylindrical ‘nose’ and a low profile flat bustle.

Cutaway views of the internal systems and layout of the turret. Photo: Presidio Press
Though it looks like two, there were actually three hatches in the roof of the turret. There was a small hatch on the left for the loader, and atop the turret, a commander’s cupola which featured five periscopes and a mount for a .50 caliber (12.7mm) machine gun. These hatches were placed on top of the third hatch, which was a large square which took up most of the middle of the roof. This large hatch was powered and allowed a larger escape route for the crew, but also allowed internal turret equipment to be removed easily. In front of the loaders, hatch was a periscope, there was another above the gunner’s position.
Behind the large hatch was the ejection port for spent cartridges. To the right of this was the armored housing for the ventilator. On each side of the turret were ‘frogs eyes’, the armoured covers for the stereoscopic rangefinder used to aim the main gun.

Gun

The initial Rheem concept had the gun rigidly mounted without a recoil system in a cast, low silhouette oscillating turret. The gun protruded from a long, narrow nose. The gun featured a quick change barrel, was basically identical to the 120mm Gun T123E1, the gun being trialed on the T43. However, for this turret, it was modified to accept single piece ammunition, unlike the T43 which used separately loading ammo. This new gun was attached to the turret via a conical adapter that surrounded the breech end of the gun. One end screwed directly into the breech, while the front half extended through the ‘nose’ and was secured in place by a large nut. The force created by the firing of the gun and the projectile traveling down the rifled barrel was resisted by rooting the adapter both the breech block and turret ring. As there was no inertia from recoil to automatically open the horizontally sliding breech block, a hydraulic cylinder was introduced. Upon firing the main gun this hydraulic cylinder was triggered via an electric switch.
This new variant of the T123 was designated the 120mm Gun T179. It was fitted with the same bore evacuator (fume extractor) and muzzle brake as the T123. The gun’s rigid mount was designated the T169, making the official nomenclature ‘120mm Gun T179 in Mount T169’
It was proposed that two .30 caliber (7.62mm) machine guns would be mounted coaxially. This was later reduced to a single machine gun placed on the right side of the gun.
In the oscillating turret, the gun could elevate to a maximum of 15 degrees, and depress 8 degrees. Projected rate of fire was 30 rounds per minute. The main gun had a limited ammunition supply due to the size of the 1-piece rounds. The T48 hull had to be modified to allow storage, but even then, only 18 rounds could be carried.

Automatic Loader

The automatic loader shared by the T77 and T57 consisted of a large 8-round cylinder located below the gun, and a ramming arm that actuated between positions relative to the breech and magazine. The loader was designed for one-piece ammunition but an alternate design was prepared for use with two-piece ammunition.
Operation: 1) The hydraulically operated ramming arm withdrew a round and aligned it with the breech. 2) The rammer then pushed the round into the breech, triggering it to close. 3) Gun fires. 4) Effect of gun firing trips the electric switch that opens the breech. 5) Rammer picks up a fresh round, at the same time ejecting the spent cartridge through a trap door in the roof of the turret bustle.

A diagram of the loading process. Photo: Presidio Press
Ammunition types such as High-Explosive (HE), High-Explosive Anti-Tank (HEAT), Armor Piercing (AP), or Armor-Piercing Ballistic-Capped (APBC) could be selected via a control panel by either the gunner or the tank commander (TC). The round could punch through a maximum of 330mm (13 inches) of Rolled Homogeneous Steel Armor.

Crew

The T77 had a crew of four men. The driver’s position was standard for T48/M48 hulls. He was located centrally in the bow at the front of the hull. Arrangements inside the turret were standard for American tanks. The loader was positioned at the left of the gun. The gunner was on the right with the commander behind him.

Fate

The T77 would share the same fate as other Rheem designed tanks such as the T69, T57 and T54. Like the T57, the T77’s development was arduously slow, and in 1957, the project was finally canceled by the US Ordnance Department. Both turrets were scrapped in February 1958.

An article by Mark Nash

Specifications

Dimensions (L-w-H) 20’10” (without gun) x 11’9″ x 10’10” ft.in
(9.3m x 3.63m x 3.08m)
Total weight, battle ready Around 48.5 tons (96 000 lbs)
Crew 4 (Commander, Driver, Loader, Gunner)
Propulsion Continental AVDS-1790-5A V12, AC Twin-turbo gas. 810 hp.
Transmission General Motors CD-850-3, 2-Fw/1-Rv speed GB
Maximum speed 30 mph (48 km/h) on road
Suspensions Torsion bars
Armament Main: 120 Gun T179 Sec: 1 Browning M2HB 50. cal (12.7mm), 1 cal.30 (7.62 mm) Browning M1919A4
Production 2

Links & Resources

OCM (Ordnance Comittee Minutes) 36741
Presidio Press, Firepower: A History of the American Heavy Tank, R. P. Hunicutt


Illustration of the 120mm Gun Tank T77 by Tank Encyclopedia’s own David Bocquelet.

Categories
Coldwar American Prototypes

Chrysler K (1946)

U.S.A. (1946)
Heavy Tank Concept – None Built

The Chrysler K was an American heavy tank prototype designed in response to the increasing interest in heavy tanks at the end of the Second World War. The growth in interest was thanks, in no small part, to the discovery of German plans for super heavy tanks such as the Maus and E100. Most importantly, however, it was the appearance of the Soviet IS-3 at the Berlin victory parade in 1945 that really jump-started the process.
The appearance of the IS-3 sent a chill down the spine of all major allied powers. Each nation invested large amounts of time, energy, and resources in heavily armored tanks with powerful main armaments, not least the USA, whose only heavy tank was the M26 Pershing. This vehicle was considered to lack the required firepower and protection to face tanks such as the new IS-3.
One of these early designs was a submission from the Chrysler Motor Corporation. Called the ‘Chrysler K’, it would be armed with a 105 mm main gun, and armor up to 18 cm (7 inches) thick.

Soviet IS-3 Heavy Tanks at the Berlin Victory parade in 1945. This pike-nosed heavy tank was the catalyst for many western heavy tank designs. Photo: Wikimedia Commons

Background, the Stilwell Board

On 1st November 1945, the ‘Stilwell’ Board was convened, named after the man heading the meeting, General Joseph W. Stilwell. The official designation, however, was ‘War Department Equipment Review Board’. The findings of this board, submitted in a report on 19th January 1946, agreed, for the most part, with earlier recommendations that Light, Medium, and Heavy tanks should all be developed. However, experiments with Super Heavy tanks, such as the T28/T95, would be abandoned. Another omission from the report was the development of dedicated tank destroyers, following the Armored School’s (based at Fort Benning, Georgia) opinion that the best anti-tank weapon would be another tank. As such, a Heavy tank was favored in tank versus tank combat due to powerful guns and thick armor.

Chrysler’s Submission

The famous motor car company, Chrysler, based in Michigan, submitted their design for an unconventional Heavy tank to the Armored School in a presentation by a Mr. F. W. Slack at Fort Knox on 14th May 1946. It would be known as the ‘Chrysler K’. The origin of the ‘K’ may lie with Kaufman Thuma Keller, the president of the Chrysler Corporation from 1935 to 1950, and advocate of the creation of Detroit Arsenal (DA). It is quite possible that the tank was named after him, given his position at Chrysler, and his relationship with the military thanks to DA.

Kaufman Thuma Keller, President of the Chrysler Corporation 1935-1950. Quite possibly the man behind the ‘K’. Photo: mountjoyhistory.com

Design

Chrysler’s design would incorporate a number of features that were sophisticated for the period they were designed in. These included an electric motor, remote controlled secondary armaments, and a ‘Driver in Turret’ arrangement.

Armament

The 105 mm Tank Gun T5E1 was chosen as the main armament for Chrysler’s heavy tank. Designed in 1945, it was the popular choice for American Heavy tanks at the time and was also mounted on vehicles such as the Heavy Tank T29, and the Super Heavy Tank T28. The T5E1 had a medium velocity of 945 m/s (3,100 ft/s). A variety of ammunition (which was two-part, separately loading. eg, projectile loaded then charge) allowed it to be as good a bunker buster as a tank killer, with the gun proving capable of penetrating concrete as well as metal. Ammunition types included APBC-T (Armor-Piercing Ballistic-Capped – Tracer), HVAP-T (High-Velocity Armor-Piercing – Tracer), (Armor-Piercing Composite Rigid – Tracer) APCR-T and HE (High Explosive). The APBC-T shell could penetrate 135 mm (5.3 in) of armor at a 30-degree slope or 84 mm (3.3 in) of armor at a 60-degree slope, 914m (1,000yd).
At 7.53 m (24 ft 8 in), the barrel of the weapon was rather long. It was concluded that if the turret was mounted in the usual place, ie, centrally, the gun would become hazardous in convoy travel or whilst maneuvering. As such, the decision was made to place the turret at the back of the tank, off-setting the length of the gun. This design choice resulted in the vehicle having an overall length of 8.72 m (28 ft 7.5 in). This is just 7.62 cm (3 in) longer than the M26, despite the 105 mm gun being 16.5cm (6½ inches) longer than the 90 mm gun of the M26. The gun could elevate up to 25 degrees, and depress to 4-degrees.
Secondary armament was machine gun heavy, with three .50 Caliber (12.7mm) heavy machine guns and two .30 Caliber (7.62 mm) machine guns. One of the .50 Cal. machine guns was mounted coaxially with the main gun, the other two were placed in secondary turrets on the left and right rear corners of the hull. They had a limited horizontal traverse, but could be elevated upwards to defend against air attack (quite how practical this was is debatable). The two .30 Cal. machine guns were placed in blisters at the left and right top corners of the upper glacis. It is unknown whether they were ball mounted and had a degree of traverse, or whether they were completely fixed. All of these weapons were controlled and fired via a remote control system that was an improved and simplified version of the turret control system on the B-29 Superfortress bomber. If they were fixed, it is debatable as to whether these weapons would’ve been any use at all. Fixed, forward mounted machine guns like these were abandoned from designs long before the ‘K’. As an example, the original versions of the Medium Tank M3 and M4 Sherman had fixed forward facing MGs, but not the later ones. The layout of Machine guns on the hull is similar to an Army Ground Forces (AGF) design for a medium tank.

Turret

One problem with the T5E1 gun was that it had a long breech. Still, the turret had to accommodate this, 100 rounds of 105 mm ammunition, and the crew which consisted of a commander, gunner, loader, and the driver. As a result of this, the turret diameter had to be wider than anything previously designed for an American tank. The internal diameter was 2.9 meters (9 foot 10 inches), while the turret ring was 2.1 meters (86 inches), as opposed to 1.75 meters (69 inches), the largest of previous designs. It stated that 100 rounds of the separately loading 105mm ammunition were carried by the tank and that they were stored circumferentially around the turret. However, an investigation into this reveals that there simply isn’t enough room for all 100 rounds inside. Though it isn’t stated in any source material, it is reasonable to suggest that ammunition was stored under the turret, as there is enough unaccounted for space from the bottom of the hull to the floor of the turret. As stated this is speculation but it is not unreasonable as it was a very common practice.
The turret was hemispherical in shape, and cast in construction – this shape offered excellent ballistic protection. The turret face was 18 cm (7 inches) thick, while the rest of the casting was 7.62 cm (3 inches) thick. Ammunition was stored circumferentially at the rear of the turret. The face of the turret was reinforced with a mantlet consisting of a large, thick disc. The exact diameter and thickness of this mantlet plate are unknown.
An unusual feature of the Chrysler, for the time, was the fact that the driver was located in the turret with the rest of the crew. It wasn’t the first time that a tank could be driven from the turret, however, as a remote control box in the turret of the T23 allowed control from within should the driver be knocked out. It was believed that having all the crew in the turret provided better communication and cooperation. The turret still had the ability to rotate 360-degrees. The driver’s seat (and presumably controls) were geared so that they were always linear (always facing forward in relation to the hull) to the tanks hull, no matter where the turret was pointing. His position was surrounded by pericopes so no matter where he was in relation to the turret, he would always be able to see where he was going.
The exact crew positions in the turret are unknown, but looking at the position of hatches and pericopes we can make an educated assumption. It would appear the Driver sat at the front left of the turret with the Loader behind him. The gunner sat at the front right, with the Commander at his rear.


A small-scale mock-up of the ‘K’ tank. This is as far as the project got. Note that the rear machine gun turret is traversed out slightly. Photo: Presidio Press.

Propulsion

With the turret moved to the rear of the tank, the engine would now take up the space left at the front end. The power requirements for the vehicle were based on a US Ordnance Department idea calling for 20 hp per-ton for this projected 60-ton tank. The gasoline-fueled engine was an unspecified design by Chrysler and was powerful with a projected output of 1,200 hp.
The engine was placed in the front end of the hull was to was to be connected to two electric motors that formed the tank’s final drives at the front of the vehicle. This system is similar to that used on the Medium Tank T23 prototype. The electric drive system on the ‘K’ tank was designed by a Mr. Rodger.
The engine system was fed by 600-US gallon (2727 liter) fuel tanks. The exact number of tanks is unknown, but it is likely to be at least two, judging by other American heavy tanks of the time.

Suspension

The suspension was the usual torsion bar type. There were eight twin road-wheels per side, with the idler at the back and the drive sprocket at the front. The idler was the same type of wheel used for the road wheels. The return of the track was not supported by rollers. This is known as a flat track suspension and is common on Soviet tanks such as the T-54 and so on. The track was 76.2 cm (30 inches) wide.

Hull

The hull was rather square in its overall shape, with the frontal plate 18 cm (7 inches) thick and angled at 30-degrees. Such angling brought the effective thickness up to roughly 36 cm (14 inches). Armor on the tank’s sponsons was less impressive being just 7.62 cm (3 inches) thick. They were sloped inwards slightly at around 20-degrees, this would’ve made the effective thickness 8.1 cm (3.1 inches). A 25 mm (1 inch) thick armored floor protected the underside of the vehicle. The tank was 3.9 meters (12 foot 8 inches) wide. For rail travel, the sponsons and outer halves of the road-wheels could be removed.
The overall height of the ‘K’ tank, turret included, was 2.6 meters (8 foot 8 inches) tall. This was 7.62 cm (3 inches) shorter than the M26. Altogether, the tank was projected to weigh 60 tons.

A modern side-on schematic of the Chrysler ‘K’ heavy tank concept. Photo: Tank Archives Blogspot.

Fate

Funds for tank design gradually dwindled after the Second World War. As such, the Chrysler K tank never left the development stage, with only line drawings and a scale model produced. Unfortunately, the drawings and scale model are not thought to survive, and only a photo of the model remains. The project was abandoned, with attention turning to more conventional tank designs such as the Heavy Tank T43, which would eventually become America’s last heavy tank, the 120 mm Gun Tank M103.
Some of the design features of the ‘K’ tank were carried over into future tank projects. The ‘Driver in Turret’ concept was utilized on the M48 Patton based M50/53 self-propelled gun, and also the MBT-70 and subsequent prototypes. To the east, the Soviets also used this concept in their prototype medium tank, the Object 416.

The Other ‘K’

This heavy tank was not the only tank designed by Chrysler to bare the ‘K’ designation. Twenty-two years later, in 1968, Chrysler would put forward another design intended to be a possible upgrade of the 105mm Gun Tank M60. The design featured a brand new, comparatively smaller turret and a new main gun.
Two guns were tested on the tank. One of these was the 152 mm Gun Launcher XM150, a modified version of the gun used in the MBT-70 project. The gun could fire conventional Kinetic Energy (KE) rounds, or launch Anti-Tank Guided MIssiles (ATGMs). The other gun was the 120 mm Delta Gun. This was a Hyper-Velocity Gun that was smooth-bore and fired an Armor-Piercing Fin-Stabilised Discarding-Sabot (APFSDS) round. The gun also used combustible cartridge cases, meaning the entirety of the round would ignite upon firing, much liked the bagged charges used on the 120 mm gun of the British Chieftain.
Another modification that Chrysler designed for the M60 was for the suspension, specifically the torsion bars. A modification by Chrysler allowed the wheels to have an extra 45 percent travel when actuating on their suspension arms.
Despite notable merits to the Chrysler’s ‘K’ tank, the design was not accepted into service. Two mockup turrets were constructed and tested on M60 hulls, but at the time, all spare funds were being spent on equipment for the lingering Vietnam War. As such, all work on the vehicle was dropped.

Chrysler’s other ‘K’ tank from 1968. This time being a possible upgrade of the M60. This is the first version with the MBT-70s XM150 152mm Gun/Launcher. Photo: Presidio Press

An article by Mark Nash

Specifications

Dimensions (L-w-H) 8.72 x 3.9 x 2.6 Meters (28 ft 7.5 in x 12ft 8in x 8ft 8in)
Total weight, battle ready 60 tons
Armor Bow: 18cm (7in), angled at 30-degrees (36cm, 14in, effective)
Sides: 7.62cm (3in), angled 20-degrees (8.1cm, 3.1in, effective)
Turret Face: 18cm (7in)
Turret Sides/Top/Rear: 7.62cm (3in)
Crew 4 (Commander, Driver, Loaders, Gunner)
Propulsion 1,200 hp Chrysler Petrol/Electric engine
Suspensions Torsion bars
Armament Main: 105mm Gun T5E1 Sec: 2 x Browning M2HB 50. cal (12.7mm) MGs in remote turrets, 3 x cal.30 (7.62 mm) Browning MGs. 2 x in fixed mounts on the bow, 1 x coaxial.

Links & Resources

Presentation by Mr. F. W. Slack, 14th May 1946. Original document provided by The Richard Hunnicutt Collection in the at the National Armor and Cavalry Museum Archives. Thanks for this are also extended to the Museum’s Curator, Rob Cogan.
Presidio Press, Firepower: A History of the American Heavy Tank, R. P. Hunicutt
Presidio Press, Patton: A History of the American Main Battle Tank, Vol. 1, R. P. Hunicutt


Profile of the Chrysler ‘K’ Heavy Tank with a speculative livery of Olive Drab with basic US Markings. Both the color and markings were commonplace at the time. Length and height wise, the ‘K’ wouldn’t have been much larger than the United States then serving tank, the M26 Pershing. At the time, the M26 was considered a Heavy Tank.


A head-on view of the ‘K’ Heavy Tank. This view shows just how wide tank would’ve been. While the ‘K’ was only a maximum of 7.62 cm (3 in) taller and longer than the M26, it was much wider at 3.9 m (12ft 8in), approximately 40cm (16in) wider than the M26. Note also, the 76.2 cm (30 in) wide tracks, and how far the remote rear turrets extend from the hull sides.

Both of these Illustrations were modeled by Mr. C. Ryan and were funded by our Patreon Campaign.

Categories
Coldwar American Prototypes

120mm Gun Tank T110

U.S.A (1954)
Heavy Tank Concept – Wooden Mockup Built

Improving the Breed

Even while the T43 (M103) was still in development, the U.S.A. was not done with attempts at making better heavy tanks. Development was split into two schools of thought. One based its work on the T43, leading to the T57 and T58 auto loading tanks; and the other started from scratch.
In June 1954, the Detroit Arsenal held its third Question Mark Conference, the goal of which was brainstorming ideas for new heavy tanks. Suggested designs included the TS-2, TS-5, TS-6, and TS-31.
Conditions these proposals had to meet were that a prototype had to be constructed within two years (hence “TS”, for “Tracked vehicle Short Development”), and it had to be able to fit within the confines of the Berne International Clearance Diagram; a code of standardization for rail tunnels established at the international conference at Berne, Switzerland, in 1913. (There is no single Berne National Tunnel, as claimed by Hunnitcutt’s ‘Firepower’; this was merely a building code for rail tunnels)
The TS-2 and TS-5 were both armed with a 105 mm (4.13 in) T210 smoothbore gun; in a turret on the TS-2, and in a fixed casemate on the TS-5.
The TS-6 and TS-31 were armed with the 120 mm (4.72 in) T123E1 gun; again in a turret on the TS-6, and casemate on the TS-31.
Power for the tanks would have been supplied by either a 700 hp Continental AOI-1490-1 engine with an XT-500 transmission (TS-2 and TS-5), or an 810 hp Continental AVI-1790-8 with an XT-500 transmission (TS-6 and TS-31).
In the end, the TS-31 was chosen for further development; it had a gimbal gun mount, and was estimated to weigh 45 tons. Chrysler was assigned to the development of the TS-31, which was given the designation “120mm gun tank T110”; at the same time, the T43 was entering pre-production.
The TS-31/T110 had a driver in the hull, a gunner to the left of the gun, a commander and his machine gun cupola to the right of the gun, and two loaders. It was rear-engined and had six roadwheels on either side. Armor was to be as thick as 9 inches (228.6 mm) on the gun mantlet. Despite the TS-31 concept being chosen as the winner, it still was slightly too big to fit through the Berne Clearance Dimensions. Additional problems were found with the off-center commander’s cupola: the additional metal to support it added to the tank’s weight and increased its size. These flaws led to Chrysler redesigning the tank.

Losing Some Weight

The second draft was an improvement over the original TS-31. It was slightly smaller, becoming shorter and the front becoming flat. The driver was moved into the casemate, to the left of the gun, with the gunner being moved to the right of the gun. Behind the driver and gunner were two loaders and the commander behind them. The commander was placed directly in the middle of the tank, leaving him to sit almost directly atop the engine and with his feet worryingly close to the gun breech. Despite all this, it was still too big to fit through the Berne Clearance Dimensions. Size, in addition to the Detroit Arsenal’s disapproval of the driver’s position, led to a second redesign.
The third draft was sort of a reversion to the original; the driver was moved back to the hull outside of the casemate, and the gunner was moved back to the left of the gun. The commander’s turret was moved slightly forward, so he would no longer have to sit on the engine, but was now forced to sit in a very awkward and cramped position in order to avoid being crushed by the gun’s recoil every time it fired. The casemate reverted to being rounded at the front. The third draft was no smaller in size than the second.

Detroit Fires Back

The Detroit Arsenal replied to Chrysler’s two proposals with the fourth draft of the T110. The casemate was moved to the back, hanging over the rear of the tank. The transmission was moved to the rear as well, joining the engine. In its place up front was a massive fuel tank, nearly encompassing the driver. The power plant (which was now a Continental 700 hp AOI-1490) was pushed to the left to afford the commander a more comfortable (but still probably hot) position on the far rear right. The suspension was changed to a more conventional (for the Americans) type, with smaller road wheels; although the original draft is without them, return rollers would have been necessary.

Hammering out a Design

Chrysler rejected the Detroit Arsenal’s idea to put the casemate on the very back on the tank and kept it in the middle. The driver was moved back inside the casemate, to the right of the gun. You may know this vehicle as the T110E3 or E4, although these designations are completely fictional. Chrysler originally tried to simplify maintenance on this design by allowing the engine to be pulled out, on rails, via a hatch in the rear of the tank. This feature created rigidity issues and the engine was returned to a standard position, now turned lengthwise in the tank. This new engine placement again left the commander stuck between the engine and the gun breech. The gun mantlet, which had been relatively tiny before, was much bigger in this iteration; weighing 2 tons and being 9 inches (228.6 mm) thick. The tank was now short enough to fit through the Berne Tunnel, but it was still too wide.
This version of the T110 was the first to have serious work done on it. A wooden mockup was built and engineering diagrams were drawn up. Gun traverse was 15 degrees to each side, with 20 degrees of gun elevation and 10 degrees of gun depression. Armor was 5 inches (127 mm) at a 60 degree slope from vertical. Secondary weaponry comprised the commander’s .50 cal (12.7 mm) M2 Browning, as well as a .30 cal (7.62 mm) paired with the main gun.
Artist's interpretation of design five
Artist’s interpretation of design five
The original TS-31/T110
Small scale model of design five
At some point, Chrysler realized that there was no need to stick with a casemate design, as a turret could be accounted for within the weight requirements for the tank. In its sixth iteration, the T110 was completely changed, becoming a far more conventional tank. The driver was moved to the middle of the hull, under the gun barrel. The crew was reduced to four instead of five men by dropping a loader. To ease the life of the remaining loader, a gun rammer was fitted. The gunner was on the left of the turret, with the commander above and behind him, and the loader on the right. This, the last version of the T110, shared the 85 inch (2.16 m) turret ring with the M103. Engineering diagrams and a full-size mockup were made, but by this time the T43E2 had been built and showed promise. The success of the M103, as well as changing ideas in terms of tank design, were the doom of the T110, and the project was canceled.
Artist's interpretation of design six
Artist’s interpretation of design six
The original TS-31/T110
Small scale model of design six
Even the definitive version of the T110 failed its main goal, as it was still too big to fit through the Berne Clearance Dimensions.

The original TS-31/T110
The original TS-31/T110
Chrysler's first revised T110
Chrysler’s first revised T110
Chrysler's second revised T110
Chrysler’s second revised T110
The Detroit Arsenal's T110 counter-proposal
The Detroit Arsenal’s T110 counter-proposal
The fifth T110 design -Chrysler
The fifth T110 design -Chrysler

The fifth T110 design -Chrysler
The original TS-31/T110
Schematics of the fifth T110 design
The sixth T110 design -Chrysler
The sixth T110 design -Chrysler
The original TS-31/T110
Schematic of the sixth T110 design

T110, Draft Six specifications

Total weight, battle ready Probably around 50 tons
Crew 4 (driver, gunner, commander, loader)
Propulsion Continental 700hp AOI-1490
Suspension Torsion Bar
Armament 120 mm (4.72 in) T123E1 rifled cannon
Total production A few wooden mockups

Sources

Presidio Press, Firepower: A History of the American Heavy Tank, R.P. Hunnicutt.
(This is also the source for every image used in the article)
Originally published on November 13, 2016.


The fifth T110 design submitted by Chrysler. The 120 mm cannon is mounted in a fixed superstructure, with a machine gun armed commander’s cupola on the roof. Illustration by Jaroslaw “Jarja” Janas.

Categories
Coldwar American Prototypes

155mm Gun Tank T58

U.S.A. (1952)
Heavy Tank Prototype – 2 Turrets Built

In the early 1950s, the American military’s quest for a powerful new heavy tank was well underway. The T28, T29, T30, T32, and T34 projects had all ceased in favor of the 120mm Gun Tank T43, which eventually became America’s last heavy tank, the M103.
While still in development as the T43, however, there were parallel projects competing for the role of America’s next heavy tank. One of these projects was the 120mm Gun Tank T57. It used the same hull as the T43, but incorporated new technologies for the turret. The turret was of the oscillating kind, but it was also outfitted with an autoloading mechanism.
In the Army Development Guide of December 1950, both the T43 and T57 were expected to more than meet the requirements of the military and be a worthy adversary of Soviet armor such as the infamous IS-3. However, in the Tripartite Conference of Armor and Bridging of October in 1951, it was recommended that a 155mm gun armed tank be developed instead.

A mockup of the T58 Heavy Tank. Photo: Presidio Press

Development

A list of recommended characteristics for this new heavy tank was outlined in a paper on the 18th of January 1952. Such recommendations included a gun that exclusively fired HEAT (High-Explosive Anti-Tank) or HEP (High-Explosive, Plastic. Otherwise known as HESH – High-Explosive Squash Head) rounds. This paper also recommended the construction of two prototype turrets complete with autoloaders and 155mm guns for installation on T43E1 chassis. The resulting vehicle received the designation of 155mm Gun Tank T58.
On the 10th of April 1952, a contract was drawn up with United Shoe Machinery Corporation of Beverly, Massachusetts for the design, development and manufacture of the two pilot turrets.

Hull

The hull that was used for the project was the same as that of the 120mm Gun Tank T43, which would later be serialized as the M103, America’s last heavy tank. Armor on the hull was the same. The cast ‘beak’ was 3.9 – 5.1 in (100 to 130 mm) thick.
An 810hp Continental AV1790 12-cylinder air-cooled gasoline engine propelled this chassis to a speed of around 21 mph (34 km/h). The tank’s weight was supported on seven road wheels attached to torsion bar suspension. The drive sprocket was at the rear while the idler wheel was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. The return of the track was supported by six rollers.

Turret

The T58’s turret was one of the largest oscillating turrets ever designed, at approximately ¾ the length of the hull. Changes had to be made to the T43/M103 hull to accommodate the new large turret. When initially tested on one of the hulls, the turret bustle would collide with the mufflers of the main engine and auxiliary generator located on the engine deck. To fix this issue, the mufflers were relocated 20-inches (51cm) to the rear. A new travel lock was added to the deck to accommodate the larger gun.
This turret had similarities to the T69 medium tank prototype, in that its roof had multiples ways of ingress and egress. The turret roof was constructed from two removable plates. The rear plate was bolted in place, while the front section, like the T69, was hinged and could be opened outward by use of a hydraulic piston. The large opening made it easier to exit the turret in an emergency. In the open position, this opened section also provided a shield for the crew while evacuating. These sections were designed to be easily removed to permit installation of the autoloader mechanism and other components.
A ventilator was placed at the rear-right of the turret atop the bustle to vent gases and smoke produced when the gun is fired.

Line drawing of a face-on view of the T58. Note the size of the turret. Photo: Presidio Press

Links, Resources & Further Reading

Presido Press, Firepower: A History of the American Heavy Tank, R. P. Hunnicutt
An official US Government report dated April 1954. READ HERE
On History of War


A cut-away view of the inside of the T58’s turret. Photo: Presidio Press

Armament

Originally, it was planned to utilize the 155mm Gun T80. This proved unnecessary as the chosen ammunition for the gun was of the chemical type and did not require the high-velocity granted by the T80. Designers instead opted for a lighter weight version of the lower velocity 155mm Gun T7, the gun developed for the Heavy Tank T30. Firing HEAT through this gun, the maximum armor that could be penetrated (angled at 0 degrees) was 16 inches (406mm).
This modified version of the T7 was originally designated as the 155mm Gun Howitzer T7E2. It was later changed, however, to ‘155mm Gun Howitzer T180’. There was no actual change to the gun, just a change in nomenclature. The T180 differed greatly from the original T7 though. The breech block was changed from a horizontal to a vertically sliding type. A bore evacuator (fume extractor) was added towards the end of the gun, and a T-shaped blast deflector installed on the muzzle. The gun tube wall was thickened and the chamber lengthened about an inch (~25mm) to accommodate the plastic closing plugs used on the cartridge cases of the two-part ammunition.
Unlike the T57 that had a rigidly mounted gun, the T58 was outfitted with a four-cylinder hydro spring recoil system in a mount designated the T170. There were 2 springs to each side of the breach. To save space and remove the need of extending the length of the turret, the recoil of the gun was limited at 12 to 14 inches.
Secondary armament consisted of a coaxial .30 Cal (7.62mm) Browning machine gun, and a .50 cal (12.7mm) Browning heavy machine gun mounted atop the commander’s cupola. The oscillating turret provided an elevation of 15 degrees, with a depression of 8 degrees. The original specifications included a second coaxial machine gun, but this was not included.
The main gun was aimed via periscopic sights. There was one lens on each side of the turret, known as ‘frog’s eyes’. These types of sights were used on many American tanks from the early 1950s onwards, including such tanks as the T69, M48 and M60.
The armor on both the collar and upper part the turret was extremely thick, but exact measurements are unfortunately unknown.

Autoloader

The 155mm gun was fed by an autoloading mechanism located in the turret bustle. It was not too dissimilar to the one used on the T69 medium tank prototype, consisting of a 6-round cylinder magazine with an incorporated rammer. On the T69, it actuated up and down during the loading sequence. On the T58, due to the size and sheer weight of a fully loaded magazine, the cylinder was fixed in place.

Two diagrams looking at the front and back of the auto-loading mechanism. Photo: Presidio Press
The loading sequence was thus: The loader used an internal, electrically powered hoist attached to the turret roof to remove one of the 95 pound (45kg) shells from the ready rack and insert it into the loading tray of the cylinder. The round was then slid into an empty cylinder chamber. The loader then selected the requested ammo type by manually rotating the cylinder with a hand crank. The separately-loading ammunition (projectile then charge) was rammed into the breach as one unit. After firing, the empty propellant cartridge was ejected back into the cylinder, where it was removed by the loader before the sequence began anew.

Crew

The crew consisted of a Commander, Gunner and Loader located in the turret and Driver in the front of the hull. The Gunner was located at the front right of the turret, the Commander sat behind him under a vision-cupola. The Loader was positioned on the left of the turret under his own hatch.

Fate

Work on two pilot turrets continued into 1956 despite numerous design changes during production and delays in obtaining and producing various parts required for assembly. By this time, however, trends had shifted, and a tank such as the T58 was no longer thought a necessary to the military.
The T58 project, along with the T57 and many other projects, was canceled on the 17th of January 1957. Following this outcome, both pilot turrets were scrapped. All that survives today are a few photos and government reports.

An article by Mark Nash

Specifications

Dimensions (L-w-H) 37.14 x 12.34 x 9.45 ft (11.32(oa) x 3.76 x 2.88 m)
Total weight, battle ready Around 62.5 tons (125 000 lbs)
Crew 4 (Commander, Driver, Loaders, Gunner)
Propulsion Continental AV-1790-2 V12, AC Twin-turbo diesel 810 hp.
Transmission General Motors CD-850-3, 2-Fw/1-Rv speed GB
Maximum speed 21 mph (34 km/h) on road
Suspensions Torsion bars
Armament Main: 155mm Gun Howitzer T180 Sec: 1 Browning M2HB 50. cal (12.7mm), 1 cal.30 (7.62 mm) Browning M1919A4
Production 2


Illustration of the 155mm Gun Tank T58 by Tank Encyclopedia’s own David Bocquelet.

Categories
Coldwar American Prototypes

76mm Gun Tank T92

USA (1952-58)
Light Tank – 2 Prototypes Built

In May of 1952, the hunt was already underway for a new light tank that would replace the M41 Walker Bulldog which had only entered service the previous year. Three companies were competing for a production contract. These were the Cadillac Motor Car Division (CMCD) of General Motors Corporation (GM), Detroit Arsenal (DA), and Aircraft Armaments Incorporated (AAI).
Cadillac and Detroit would compete individually with their own designs. These would both be designated as the T71. The T71 was rather traditional in its design when comparing it to AAI’s proposed tank, which was rather unique, to say the least. As such, the latter vehicle would receive the designation of T92.

The initial T92 prototype. Photo: Presidio Press

Development

After review, a contract was handed to the AAI to produce a full-scale mock-up. Their tank was considered an extremely innovative design which offered greatly improved performance over previous light tank models. This also meant that it included newly developed features including some which were so novel they had never been tested before, which is considered risky when building a new tank.
The Chief of the Army Field Forces and the Assistant Chief of Staff authorized development of the tank in late July 1953. The United States Ordnance Technical Committee also approved the design in March 1954, with clearance given to produce a pilot vehicle. On the 18th June 1954, AAI was given permission to build an additional pilot vehicle. Meetings on the 5th of November 1954 and 27th of January 1955 resulted in recommendations for numerous design changes.
Development continued into January 1956, at which point the competing T71 project was canceled. This was thanks, in no small part, to the rapid progression of the T92, and the troublesome development of the T71 which ran into funding issues.

Design

Hull

Welded steel armor and castings formed the hull of the T92, which was extremely flat and made up of oblique surfaces. The hull was wedge-like in its shape and extremely low profile. One of the more outlandish thoughts behind the shape was that it would help to deflect the blastwave of a Nuclear Blast should it have taken one head on.

A comparative image showing the size difference between the T92 and the M41 Walker Bulldog. Photo: Presidio Press
The armor thickness was almost identical to the M41, which was 31.7mm (1.2 inches) at its thickest, but it was considerably lighter at 18-tons than the 26-ton Walker Bulldog. This was due to a reduction of overall parts, with some constructed from Aluminum alloy. Such parts included the access doors of the power plant, generator, and battery compartments. The fenders were constructed from a blend of Aluminium and fiberglass reinforced plastics. It was designed to be as light as possible to allow it to be air-transported or deployed via-parachuted drop.
Access into the hull, as well as the various cupolas over the various crew positions, was through a rather large, square two-part armored door in the rear. Each door was fitted with a vision block. To the left of the doors was stowage for the pioneer tools (shovel, pick-ax, etc). To the right was stowage for two fuel “Jerry” cans. These were stored vertically with one on top of the other.

A view of the rear of the tank showing the two-part door and stowage positions. This is the updated vehicle with the added idler wheels. Photo: Presidio Press

Mobility

The T92’s power pack consisted of a 357 horsepower AOI-628-1 (AOI: Air-cooled, Opposed, Inline) engine that was located in the front right of the hull. It was connected to an Allison XT-300 transmission providing 6 forward and one reverse gear. The top speed on road was 35 mph (56 km/h). There were two air intakes; the large grill on the upper glacis and a ‘mushroom’ ventilator at the right front of the turret. The exhaust ran to the back of the vehicle under the right sponson, ejecting fumes through a grille at its rear. The whole power pack (engine & transmission) could be removed and installed as one piece. Fuel was stored in two 75-gallon (341 liters) bladder-type tanks for a total of 150 gallons (682 liters). These bladders were located at the rear of the hull.
The driver sat to the left of the engine, just in front of the turret ring and was protected by a steel firewall. The vehicle was operated by two small control handles that were used to steer and brake. He had a hatch above his head fitted with vision blocks. It swung open to the left on a pivot. There was also an escape hatch beneath his position.
Suspension on the T92 consisted of a Torsilastic system which is not commonly used on armored vehicles. In the case of the T92, this consisted of a cylinder attached to the hull sides. This intern, consisted of a hollow shaft and a coaxial tube, with rubber between the shaft and the tube. The rubber was sulfurized to make sure the shaft and the tube were firmly attached. The Torsilastic suspension type eliminated the friction between metal parts and thus did not need to be lubricated as often as standard suspension types. The rubber acted as an elastic element, as well as a shock absorber, meaning the vehicle could be quieter and more comfortable to drive. This suspension system was also used on some LVT models and the M50 Ontos. The external nature of the Torsilastic suspension saved a great deal of room inside the vehicle that would otherwise have to accommodate the long torsion bars of a traditional suspension. There were 4 road-wheels per-side, each with a corresponding suspension unit. The drive wheel was at the front, and did not have traditional external teeth. There were long posts around the wheel which slotted in guide holes in the track which would pull it around. In the initial design, there were no return rollers. As such, the track would’ve been quite slack over the return which could result in ‘track-slap’ damage or the loss of the track. The meetings of November 1954 and January 1955 brought this to light, and it was recommended that at least two return rollers be installed. One was installed behind the suspension unit of the second road wheel, the other was installed behind the suspension unit of the last road wheel/trailing idler.
The tracks were a band type which did not require pins to hold the links together. They were mostly rubber and reinforced with steel cable, and were rather thin at just 16-inches (40.64 cm) wide. The full length of the track was 390.25 inches (9.91 meters), composed of nine separate sections. Two spare sections were stowed on the gun cradle at the rear of the turret.

Photo: Presidio Press

Turret

The turret and arrangement of the T92’s armament was perhaps the most unique feature of the vehicle. It sat on an 89-inch ring and was cleft in its design, with a large hollow in the middle cut out for the 76mm Main Armament. On either side of the gun were two cupolas which could rotate independently of the turret and were armed with machine guns. The one to the right of the gun was the commander’s and the one on the left was for the gunner. These cupolas were based on commander’s cupolas found on the M48 and M60 tanks. In the initial design of these, it was intended for both of them to be armed with Browning M2 .50 Caliber (12.7mm) machine guns. However, in the meetings of November 1954 and January 1955, it was decided to replace the machine gun in the Gunner’s cupola with a Browning M1919 .30 Caliber (7.62mm). The cupolas retained the ability to mount either weapon.
As well as the vision blocks in these cupolas, both the gunner and the commander were equipped with periscopes that enabled them to look over the gun. The cupolas were manually traversable but could also be brought into line with the main armament with the use of hydraulic slewing motors. The traverse range was 194 degrees, 10 degrees inboard forward, and 4 degrees inboard aft. The machine guns could elevate manually through a range of +60 to -10 degrees. Beneath each cupola was a suspended seat for the respective crew member to sit on, under which were drums for the machine gun ammo.
Both the gunner and commander could traverse the turret, aim and fire the main armament. The power elevation and traverse controls, as well as the gunnery controls, were mirrored in the commander’s position. The commander could override the controls to lay the gunner on to a target or engage it himself.

Illustration of the First prototype by David Bocquelet
The early version of the T92 utilized a trailing idler wheel instead of the traditional raised version which was added to the vehicle at a later date. This side view shows off the Tank’s unique profile. Illustration by Tank Encyclopedia’s own David Bocquelet.

Armament

Main armament of the T92 consisted of the 76mm Gun T185E1. This gun was ballistically the same as the 76mm Gun M32 found on the M41 Walker Bulldog and was even fitted with the same T-shaped single-baffle muzzle-break and fume extractor. This gun could fire Armor-Piercing (AP), High-Velocity Armor-Piercing (HVAP) and High-Explosive (HE) rounds.

A top down view of T92 pilot number 2 after arrival at Aberdeen on 22 July 1957. Note the unique turret and armament arangment. Photo: Presidio Press
The major differences with the weapon was its quick-change barrel, and the fact it was mounted upside down. This was to accommodate a semi-automatic loading system. The loader, who was seated in the left rear of the vehicle, placed one of the tank’s sixty 76mm rounds (28 in the main rack, 24 in the dispenser rack, 7 in the ready rack, and 1 kept in in the loading system) onto a tray behind the breach. When it is properly seated on the tray, it is automatically locked into position. The loader then held down a button for the duration of the cycle which consisted of the round being brought into line with the breach (whatever the guns state of elevation) and rammed in. The gun also featured a fully-automatic ejection system. When fired, the gun’s recoil would push the spent cartridge out of the tank through a small void in the armored box surrounding the breach. This was seen as essential as without it, the small crew compartment of a light tank like the T92 would soon fill with large, empty 76mm cases and the resulting irritant fumes.
The gun was mounted in a cradle in the center of the turret. The breach end was protected in an armored box and extended back to the rear of the turret. When the gun was depressed, the breach end lifted out of the turret roof. When the gun was elevated the breach sank into the hull. The voids created between the gun and body of the turret were covered with a canvas screen. Maximum elevation was +20 Degrees, maximum depression was -10 degrees. A semi-circular cage which acted as a guardrail was installed at the rear of the turret to protect the breach. It was to this that spare track sections were stored. Mounted above and to the left of the main gun was a coaxial Browning .30 Cal (7.62mm) M1919/M37 machine gun.

Tests

T92 Pilot No. 1 arrived at the Aberdeen Proving Grounds (APG) for tests on the 2nd of November 1956. Due to a miscommunication with constructors, some parts were missing from the vehicle. Namely, the Commander and Gunner’s cupolas. Weights were added to the positions to simulate for the automotive tests before the cupolas arrived at Aberdeen and fitted. T92 Pilot No. 2 arrived at Aberdeen on the 22nd of July 1957. This vehicle was used to evaluate the crew and their respective compartments and positions. At the time, it was expected that the T92 would enter full-scale production by mid-1962.

The T92 (with original tracks) taking part in cross-country tests. Photo: Presidio Press
Testing at Aberdeen identified a number of areas where the tank needed to be improved. These were mostly with the suspension. The band type track proved to be prone to breakage and throwing. After just 202 hours of test time, the track was replaced with the thinner (14-inch/35.56 cm as opposed to 16-inch /40.64 cm) traditionally linked tracks of the Light Tank M24 Chaffee. There were no long-term plans to keep this track for the production model, and plans were made to design a stronger band-type track. The adoption of this track necessitated the modification of the sprocket wheel to the traditional type with external sprocket teeth.
Another attempt to stop the track being thrown was the addition of a compensating idler wheel. This was the most drastic of the changes. Such idler wheels were mounted on a lot of tanks of the era, such as the M48, M60 or M103. They are attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. These were mounted on a frame that was welded to the vertical rear plate of the tank.

The revised T92 with the added compensating-idler and the tracks of the M24 Chaffee. Photo: Presidio Press

Fate

In 1957, funding was made available for two further Pilot vehicles, each one would have the suggested improvements incorporated. Delivery of these was expected by mid-1958. However, the order was canceled prior to completion.
In 1957, it was discovered that the Soviets were working on an amphibious capable light tank. This would later come to be identified as the PT-76. The T92 was assessed to see if it could be made into an amphibious vehicle. This was soon proved to be unfeasible. The effectiveness of the 76mm gun was also now called into question. In a time where the larger 90mm gun was beginning to struggle, the 76mm was now seen as obsolete. Following this, the T92 project was canceled in late 1958. Light Tank design work would then focus on the United State’s own amphibious light tank, ultimately culminating in the problematic M551 Sheridan.
One surviving T92 was preserved for a long time at the United States Army Ordnance Museum at the Aberdeen Proving Grounds in Maryland. The tank has since been removed from the site with the closure of the museum in late 2010. It was moved to Fort Lee in Virginia where it currently resides in storage.

An article by Mark Nash

Specifications

Total weight, battle ready 18 tons
Crew 4 (Commander, Driver, Loader, Gunner)
Propulsion 357 horsepower AOI-628-1
Top speed 35 mph (56 km/h)
Suspensions Torsilastic
Armament 76 mm (3 in) gun T185E1
.50 Cal (12.7mm) Browning M2
2X .30 Cal (7.62 mm) Browning M1919A4/M34
Armor Up to 31.7mm (1.2 inches) thick
Production 2 Prototypes

Links, Resources & Further Reading

Presidio Press, Sheridan: A History of the American Light Tank, Volume 2, R. P. Hunicutt
Osprey Publishing, New Vanguard #153: M551 Sheridan, US Airmobile Tanks 1941–2001
Profile Publications Ltd. AFV/Weapons #46: Light Tanks M22 Locust and M24 Chaffee, Colonel Robert J. Icks
US Archives