Category: Cold War US MBT Prototypes

40-ton Electric Drive Main Battle Tank (E.D.M.B.T.)

Post author By Andrew Hills
Post date August 20, 2021
4 Comments on 40-ton Electric Drive Main Battle Tank (E.D.M.B.T.)

This is how the EDMBT was planned to look on the outside. While this was nothing more than a mockup (with the important parts of the project being inside), it is still interesting to see. Illustration by Yuvnashva Sharma, funded by our Patreon campaign.

United States of America (1984-1987)
MBT – Models Only

In 1984, the US military was considering the problems connected with a new range of vehicles, such as the new M1 Abrams main battle tank and M2 Bradley Infantry Fighting Vehicle (IFV). As part of the evaluation of trends in future vehicles, a commission looked into the potential for electric drive systems for a 40-ton (36.3 tonne) (tank) and 19.5-ton (17.7 tonne) (APC/IFV) platform.

The US Army’s Tank Automotive Command (TACOM) issued a contract to General Dynamics Land Systems for this project – to evaluate existing electric drive technologies to use in future vehicles. This was contract number DAAE07-84-C-RO16 divided into 2 phases – a third phase was added later under contract modification P00006.

The goal was roughly that of evaluating the ‘new’ (electric drive for vehicles predates armored vehicle) technology available across a variety of platforms for what it may offer for further development. What it actually generated was the realization that electric-drive fighting vehicles were not only possible but had some valuable features worth exploring, especially with regards to a series of heavy IFV platforms. However, like so many other studies, this work faded away and the design work was abandoned. To this day, in 2020, the M1 Abrams remains in service with a conventional power plant along with numerous other armored vehicles in the US inventory. Despite the billions of dollars spent, to date, the US military has yet to capitalize on the potential of electric-drive vehicles.

Phase I: A survey of existing technology (document JU-84-04057-002)
Phase II: Generation of concept vehicles with electric drive
Phase III: A parametric study and evaluation with selection of 3 recommended concepts for further consideration

General Dynamics had actually been looking into the potential of electric drive systems as early as 1981, producing electric-drive concept vehicles for various other vehicle projects. It also had possession of a 8 x 8 wheeled, 15-ton (13.6 tonne) Electric Vehicle Test Bed (EVTB) it had paid for itself in order to test and validate electric drive.

General Dynamics EVTB (also known as the Advanced Hybrid Electric Drive vehicle). Source: DiSante and Paschen, and Khalil

The timetable for the project was for Phase I to be concluded by the end of 1984. In the end, the report on this phase was finished in July 1984 and then published in January 1985. By this time the second phase was already underway with an expected conclusion date in the latter half of 1985 to be followed by another report and, starting in the middle of 1986, Phase III running through into the start of 1987.

Why Electric Drive?

The potential of electrical drive systems was experimented with on tanks as far back as WW1. An electrical transmission offered the designer a significant freeing up of the internal layout of an armored vehicle, as the drive motors did not have to be next to the engine, and the ability to deliver continuous, reliable power in preference to mechanical systems. This is primarily because an electrical drive system has far fewer moving parts and bearing surfaces than a mechanical system. There are also major advantages, not the least of which being volume. An electrical system could be smaller than the equivalent mechanical system and smaller volume meant more internal volume in a vehicle for other things and/or a reduction in the amount which needed to be protected by armor – that means less weight too. Electrical transmissions are also quieter due to the absence of gearing and driveshafts and offer the not insignificant potential to provide electrical power for the vehicle’s systems.

Study Concepts

Some 38 possible concepts across the 19.5 (17.7 tonne) and 40-ton (36.3 tonne) vehicles were considered over four basic vehicle considerations. Plans from various companies and one university submitted concept plans for the program namely: Westinghouse, ACEC (Ateliers de Constructions Electriques de Charleroi), Unique Mobility, Garrett, Jarret, and the University of Michigan. All of the options were to consider a scheme for a baseline vehicle.

Baseline 40-ton electric drive vehicle. Source: GDLS

Baseline Vehicle Description

The baseline vehicle for the EDMBT was very similar in external hull layout to the M1 Abrams, with the automotive elements placed under a raised engine deck at the back of the tank. It had a relatively conventional external shape except that all of the crew were in the hull. Seven wheels on each side were drawn mounted on what appear to be arms, suggesting that it probably kept the same style of torsion bar suspension as on the Abrams. The most noticeable difference though is the lack of a turret, as the vehicle adopted a crewless weapon mount on the roof. This is the only weapon carried on the vehicle and is shown as an automatically loaded 155 mm STAFF (Small Target Fire and Forget) cannon with an elevation range of -7 to +20. Fitted with a single 7.62 mm coaxial machine gun, the gun carries just 15 rounds in an unusual T-shaped bustle at the back. A further 18 rounds were to be carried in the front right of the hull, alongside the driver. No armor was described but, unlike the Abrams, it had a pronounced slope to the glacis. One important note from the drawing is the location of the primary fuel tank containing 420 liters at the front, which would have added to the frontal protection. Protection levels could therefore reasonably be assumed to be at least no less across the frontal arc of the hull as on the Abrams. It is important to remember though that the vehicle shown in the drawing (LK10833), whilst more than a mere doodle of a viable tank design, should only be taken as an illustration of a possible future tank. The power plant work could just as legitimately be refitted to the Abrams – the key part of the study was not this tank per se, but a study to evaluate these power systems for tank propulsion.

40-ton (36.3 tonnes) vehicle Concepts

With four (five including one minor amendment) configurations being considered, the design task was simplified by the specification of the engines to be used. Although the AD-1000 advanced diesel engine generating 1,000 hp was selected, other options were considered across the 19.5 ton (17.7 tonnes) and 40-ton (36.3 tonnes) projects for alternative forms of power. However, in the end, other than the possibility of switching to a petrol-turbine the existing diesel engines were the only technology mature enough to be considered.

Each design was identified by concept number followed by a design number, for example ‘I-3’’ was Configuration 1 Design 3, whereas II-4 was Configuration 2 Design 4, and so on. Vehicle concepts selected to go forward from theoretical design to a drawing stage were all allocated a drawing number starting AD-8432-xxxx.

For the 40-ton (36.3 tonnes) concept, just two candidates were identified for further study – these were I-3 and IV-2. I-3 was designed by Garret and used a larger version of the same system as I-10 for the 19.5-ton (17.7 tonne) vehicle. The second was IV-2 from Unique Mobility which used scaled-up versions of the dual-path AC permanent magnet system it had proposed for the 19.5-ton (17.7 tonne) IV-2 concept.

Garret Concept I-3 40-ton (36.3 tonnes) Application

The drive system for the 40-ton (36.3 tonnes) vehicle application was the same as that of the Garret I-10 19.5 ton (17.7 tonne) vehicle, namely that it used two different paths for the delivery of automotive power, one mechanical and one electrical. The electrical system alone delivered power for speeds from 0 to 15 mph (24 km/h) and, when more power was needed to go above that, the mechanical system was unlocked and coupled to the electrical system. The control unit then controlled the power between these two units.

The electrical power was provided by a permanent magnet AC generator driven by the engine rectified to DC and then inverted in order to provide power to the traction motors. The generator was an oil-cooled Garret-type rated at 400 hp and rotated at 18,000 rpm with 93.5% efficiency. The oil-cooled rectifier for this system operated at 685 Volts DC at 98% efficiency and connected to a 284 Volt AC inverter operating at 96% efficiency.

Garrett 40-ton (36.3 tonne) Concept I-3. Source: GDLS

Westinghouse 40-ton (36.3 tonne) Concept I-4. Source: GDLS

Unique Mobility 40-ton (6.3 tonne) Concept I-6. Source: GDLS

Unique Mobility 40-ton (36.3 tonne) Concept II-4. source: GDLS

Garret 40-ton (36.3 tonne) Concept IV-I. Source: GDLS

Unique Mobility 40-ton (36.3 tonne) Concept IV-2. Source: GDLS

The traction motors used rare-earth metal magnets made from neodymium which removed the problem of the cobalt-type magnets as the US had adequate stocks of neodymium. The cost of 400 of these power units for the 19.5 ton concepts was estimated to be 1985 US$145,000 per unit (just under US$350,000 in 2020 values), but for the 40-ton (36.3 tonnes) concept, the cost would be around 1985 US$240,000 (over US$575,000 in 2020 values) as it used two traction motors for each final drive.

The Garret traction motors delivered 192 hp each and were able to operate at 200% for up to 30 seconds and deliver power to the final drive units which operated at a 4:1 reduction ratio.

Cooling was an important factor in all of the systems and calculations for the Garret systems (both I-10 for the 19.5 ton and I-3 for the 40-ton) were made. For the 40-ton (36.3 tonnes) vehicle, a maximum heat rejection of 8,737 BTU/Min (9,218 KJ/ Min) was needed.

Analysis by GDLS across the 40-ton (36.3 tonnes) drive systems showed that there would be 855 hp available. The Garrett system was the better of the two for the 40-ton (36.3 tonnes) vehicle and was capable of forward acceleration from 0 to 20 mph (32.2 km/h) in under 7 seconds and reverse acceleration from 0 to 10 mph (16.1 km/h) in under 5 seconds.

Conclusion

When this study was being done, the M1 Abrams was still a relatively new tank in service with the US military. The Soviet Union was still the major enemy to worry about with potential hordes of tanks able to swamp the armies of NATO in Europe still a constant threat in the minds of the NATO Generals. Lacking the option for a quantitative advantage over the Soviets, a qualitative advantage was sought and part of that grand quest was the goal for a tank with greater protection and more firepower than any Soviet contemporary. Just as the M1 Abrams had entered service to provide that advantage, the plan was simply to make an even better vehicle. Here, a turretless design with an autoloader that offered a small target and was capable of destroying any Soviet threat, and which also had the design flexibility offered by an electric drive, was seen as a promising approach. This vehicle was certainly not the only concept at the time to try and shed the weight of a turret on the Abrams or to increase its mobility and firepower. However, no electric drive main battle tank was ever produced along these lines, as the need for such an expensive system expired along with the Soviet Union.

Of the 38 possibilities for a drive system and layout for a 19.5 ton vehicle just three systems had been identified as being suitable for investigation or development; the Belgian ACEC DC system, the Garret AC permanent magnet drive, and the Unique Mobility dual-path AC permanent magnet drive system. Yet, for this heavier, 40-ton (36.3 tonnes) concept MBT design just two ideas made the cut, the Garret (I-3) using a larger version of the system proposed and selected as a potential system for the 19.5 ton (17.7 tonne) vehicle (I-10), and the Unique Mobility concept (IV-2), once more using a scaled-up version of its system proposed for the 19.5-ton (17.7 tonne) (IV-2) concept. Clearly from a logistics point of view and likely from a cost point of view as well any system selected for this 40-ton (36.3 tonnes) project should really have as much in common with the system on the 19.5-ton (17.7 tonne) project as well. Both projects, however, came to nothing and were dropped.

The potential advantages of an electric drive have still not yet been fully exploited by the US military or other tier 1 militaries around the world. With the prospect of freeing up additional internal volume, allowing a new configuration layout, and offering improved performance, a new generation of electric-drive AFVs is possible but unlikely as militaries opt to stick to traditional tried and tested propulsion systems.

Sources

GDLS. (1987). Electric Drive Study Final Report – Contract DAAE07-84-C-RO16. US Army Tank Automotive Command Research, Development and Engineering Center, Michigan, USA
DiSante, P. Paschen, J. (2003). Hybrid Drive Partnerships Keep the Army on the Right Road. RDECOM Magazine June 2003
Khalil, G. (2011). TARDEC Hybrid Electric Technology Program. TARDEC

EDMBT specifications
Total weight, battle ready	40 tons (36.3 tonnes)
Height	70.5 “ (1.79 m) hull (raised engine deck) 104” (2.64 m) overall height
Length	296” (7.52 m) overall length, 109.84” (2.79 m) from front wheel to rear (centers)
Width	133” (3.38 m) wide (139” (3.53 m) with side skirts)
Track Width	22.83” (0.58 m) wide
Track Length on Ground	183.07” (4.65 m)
Crew	3 – driver, commander, gunner (estimated)
Propulsion	1,000 hp AD1000 Advanced Diesel engine
Speed (road)	45 mph (72.4 km/h)
Armament	autoloaded 155 mm STAFF cannon with 15 rounds in autoloader plus 18 more in hull stowage, coaxial 7.62 mm machine gun
For information about abbreviations check the Lexical Index

Cold War US MBT Prototypes Has Own Video

M-70 Main Battle Tank

United States of America (1962-1963)
Main Battle Tank – None Built

In 1962, the US Armor Association launched a competition for the design of a next generation of Main Battle Tanks (MBTs) to replace the M60 Gun Tank in light of advanced Soviet vehicles which were being developed. The goal was to gather ideas as to how people thought the tanks of 1965-1975 might look and left the various designers a lot of freedom in terms of armament and propulsion. Many designs were sent in from around the world but one very close to home came from a serving US soldier, David Bredemeir, based at Fort Knox, the home of the US School of Armor at the time. This design was to eschew conventional suspension, layout, and armament and produce a missile carrier capable of destroying any future Soviet threat. Named the ‘M-70’ (no connection to the MBT-70), presumably for the anticipated in-service date, this vehicle provides a semi-professional glimpse at some of the thinking of the era.

PFC David Bredemeir, the designer of the M-70. Source: Armor Magazine

Layout

The basic layout of the M-70 was a long slender tank. The engine, a “long slender gas turbine”, was positioned alongside the driver at the front. The turbine would power the front-mounted transmission.

Armament

The M-70 was not to be a conventional gun tank. Bredemeir eschewed the conventional cannon approach for his design and put the offensive capability for the tank in the hands of anti-tank guided missiles. This design choice was based upon the logic that it would be able to fire before an enemy tank could and to ensure a first-round hit each time. The result was that the tank was to carry a battery of 8 anti-tank guided missiles (ATGM) in each ‘fender’, the sponsons along each side above the tracks. As the missiles traveled slower than a conventional shell, they could be fired in the general direction of the enemy even without aiming, with this process then being picked up by means of the guidance as the vehicle stopped. There would then be time to guide the missile onto its target before the corresponding enemy tank had had time to stop, aim and fire its main gun. Another launcher was retained in a rotatable turret at the back of the vehicle and between 50 and 60 missiles could be carried. Storage was facilitated for them, as their fins were all spring-loaded to fold down. Of those 50-60 missiles, 20 were to be stored in the turret.

Various types of missiles were proposed, including smoke, chemical, heat-seeking, and even atomic rounds, guaranteeing these missiles were capable of taking on even the heaviest of enemy armor. The heat-seeking missiles also enabled this tank to counter enemy aircraft and it could track them itself too with a built-in onboard radar. A machine gun was mounted on the commander’s cupola.

Crew

The M-70 was to use a three-man crew consisting of commander, gunner, and driver, although the gunner also served as a radar operator. When the gunner was busy loading the missile tube, the commander could take over his duties. Of the three crew, the driver would be at the front, leaving the commander and gunner in the turret at the back. The gunner, situated on the left, would be able to operate the missile launch-tube centrally as well as the radar, and when he was otherwise engaged, the commander could take on the gunner’s duties. The commander sat in the turret on the right-hand side and had his own cupola with a machine gun.

Bredemeir’s M-70 tank design relied upon its low profile for protection and missiles for its firepower. Source: Armor Magazine

Armor

Being lower than the M60 Gun Tank would give the M-70 a higher chance of survival on the battlefield, as it would be less likely to be hit. It also meant a lighter and more maneuverable tank but it still needed armor. The result was that the M-70 was to be made out of aluminum. This, in turn, would keep the overall weight down to 20 to 25 tons (18.14 to 22.70 tonnes)

Suspension

The suspension for the M-70 was a ‘two-stage’ system, with the tracks and road wheels divided in half and connected together via a single leaf-spring holding them to a beam that ran the full length along each side. Each of those beams was then connected by a pivot arm at the front and back of the tank to a connector on the opposite side. The hull itself was not mounted directly to these track units but held via coil springs from each end of the beam instead. Only the driving axles for the sprockets would directly link the hull to the tracks units. This double-spring system was felt to provide maximum comfort. Small road wheels would spread the weight of the tank along its track and also serve to keep the overall height of the vehicle down.

Conclusion

During the 1960s, faced with the enormous growth in power of anti-tank guided missiles, many were speculating it meant the end of the conventional tank. Likewise, the potential of ATGMs outstripped the anti-armor potential for large caliber guns with the advantage of being significantly smaller and lighter. Many countries would consider and even develop ATGM-based tanks during the Cold War, but just like the US Army, they were constrained by budgets, thinking, and a conservative attitude of trying to keep developments relatively simple. The M-70 offered superior firepower to the M60 in a much smaller vehicle but in 1962, this gun-launched missile concept was already underway on the M551 Sheridan. It was never to work satisfactorily for that tank and the M-70 offered little to warrant development.

Illustration of the M-70 Main Battle Tank by Andrei ‘Octo10’ Kirushkin, funded by our Patreon Campaign

Sources

Armour Magazine January-February 1963

M-70 Specifications
Total weight, battle ready	20 to 25 tons (18.14 to 22.70 tonnes)
Crew	3 (Commander/Gunner, Gunner/Radar Operator, Driver)
Propulsion	Petrol turbine (fuel tanks under turret at the back)
Armament	ATGM launchers, 50-60 shells (incl. 20 in turret)

Cold War US MBT Prototypes Has Own Video

Lockheed/Forsyth Tank

United States of America (1962-1967)
Articulated Light Tank – None Built

Post World War 2, the United States had a glut of tanks including large stocks of M4 Shermans and new designs such as the M26 Pershing. There was, as a result, little impetus for new vehicles, even though design work, if anything, increased apace at this time.

Throughout the 1950’s, US tank designers were looking at every aspect of the problems of tank technology, from armor to propulsion and armament. Whereas a lot of development had made great strides during this time in other areas, armor was still fundamentally based upon large steel castings. Various ideas though had been tried, including compositions with glass in armor cavities and even work on bar armor to defeat incoming projectiles and the increasingly common HEAT-type warheads.

By the early 1960s though, even with a new generation of Main Battle Tanks (MBTs) at hand, the US was short of a light modern tank that was air-transportable, amphibious, well-armed, and well protected. Obviously, this is a holy grail of tank design, light-enough weight to be air-transportable but with enough armor protection to be useful in direct battle rather than just scouting or skirmish roles. The tank which was to become the M551 Sheridan was in development but this was not the only possible light tank in development at the time. Another design from the Forsyth brothers was also being planned, and this vehicle was a technological step well ahead of anything the Sheridan offered. The first glimpse of this vehicle came in a competition held by the US Armor Association in 1962, with an entry deadline of August that year.

The model from Robert and John Forsyth, which won the US Armor Association tank design competition in 1962. Source: Hunnicutt

Designers

The first thing to address in looking at this design are the designers, John and Robert Forsyth. John and Robert were brothers who were engineers living in California and worked at the Vehicle Systems Development Division of the Lockheed Aircraft Corporation in California. Over the years, they designed and developed various transportation-related vehicles, amongst other things. These included a large bus for cars to travel in and various forms of unusual traction machines including a tri-wheeled amphibious vehicle and articulated machines.

The Forsyth brothers. Source: Armor Magazine

Whether their tank design was already being considered prior to the Armor competition of 1962 is not clear, but it was certainly submitted, meaning it must have been ready before the end of August 1962.

The Need For a Light Tank

Despite a multitude of light tank designs considered during various conferences during the 1950s, it was not until January 1959 that work had begun in earnest of a new light combat vehicle under the designation AR/AAV (Armored Reconnaissance/Airborne Assault Vehicle). The specifications demanded of that design were presented in July 1959 by Ordnance Tank Automotive Command (OTAC). That vehicle was going to have to replace the existing stock of M41 light tanks, the M56 self-propelled gun and supplement/work alongside the existing main battle tanks and armored personnel carriers in service.

To meet this demand, a pilot vehicle was prepared by Aircraft Armaments Incorporated (AAI) with a 3-man crew tank in the 10-ton (9.1 tonne) class. Another company, Cadillac, designed a vehicle with a four-man crew and a little heavier. Neither of those vehicles though, as obvious by the incredibly low weight, had any reasonable protection outside of against small arms. Even so, the Cadillac proposal, although selected for development, was still woefully under-protected even outside the weight limit imposed. As a result, the allowance for weight was increased to 15 tons (13.6 tonnes) and was designated AR/AAV XM551, the progenitor of the M551 Sheridan. What that design sacrificed in height and size it made up for in armament, with a 152 mm main gun capable of firing a large HEAT (High Explosive Anti Tank) round as well as the Shillelagh missile with a HEAT warhead. Both of those weapons were capable of taking on even the heaviest contemporary Soviet armor and also provide fire support for airborne troops. Other weapons under consideration at the time were a conventional 76 mm, 90 mm, 105 mm, and even 152 mm guns, ENTAC (ENgin Téléguidé Anti-Char) (to supplement any conventional gun), TOW (Tube-launched, Optically-tracked, Wire-guided), or POLCAT missiles.

The first pilot XM551s were delivered in June 1962 for testing, with more pilots following in 1963, 1964, and 1965. Despite teething problems, the design was authorized for production and contracts issued in April 1965. The M551 went on to provide decades of service for the US military in various conflicts but it never really lived up to expectations. The armor was always inadequate and the firepower from the gun/missile system never really worked well.

A contemporary design though, offered some solutions to what became the flaws in the M551 Sheridan, whilst at the same time adding another layer of complexity to meet the demand to replace the old and obsolescent M41 Walker-Bulldog and M56 Scorpion vehicles in service. Providing a main battle tank class vehicle at a significantly reduced weight, this design was supposed to add mobility as it could go places a conventional tank, light or otherwise could not go.

Basic Layout

Having won the tank design competition with their design at the end of 1962, the Forsyth brothers and Lockheed Aircraft Corporation were anxious to secure and market the idea. The result was an embodiment in the patent application filled in January 1963, but there was nothing in that application other than the layout.

What it showed was a small tank with 5 road wheels on each side, topped with a low-profile rounded turret. Inside that turret can be seen one large caliber gun and a smaller secondary armament. Most striking in that design though is what is behind the tank, a trailer. Not just a trailer in fact, but another tracked hull, with 5 road wheels but where the armored body is taller, reaching nearly the height of the turret of the preceding vehicle. The two sections connected together through an articulated joint. The details of the articulated design would be made clear in a following application filed in July that year.

The basic design of Forsyth and Forsyth’s tank concept for Lockheed, as shown in US Patent 196779 of January 1963, illustrates a novel articulated vehicle.

The articulation was carried out by means of an assembly consisting of two rungs, the outer of which has two arms connected to the hull of one vehicle which controlled the pitch and roll between the two sections. The inner ring was mounted by means of an internally rotating ‘shoe’ to a yoke which was fixed rigidly to the other vehicle. In this way, the coupling allowed for a controlled degree of rotation between the two sections as well as movement sideways (as encountered when steering) and vertically (as encountered when climbing or descending).

The coupling between the two sections. Source US Patent 3215219

The whole construction was simple, just two fabricated sections forming a top and a bottom half of the hull fastened together. US Patent 3351374

Armor

The armor in the 1962 Armor competition was described as a steel and aluminum alloy with a maximum thickness of 76 mm to 150 mm (3 to 6 inches). This was clearly subject for more thought and the focus of the design submitted for patent in July 1963 was the armor. Instead of relying on a homogenous steel plate that was face hardened and was heavy and vulnerable to shaped charges, the Forsyth brothers envisaged a new system. This system consisted of a series of layers, a first and second layer of rigid armor spaced apart from each other which the cavity between them filled with a multitude of different armor panels, which were themselves held apart by a filler material proposed to be cellular or a foam-type material. This armor-system extended across the entirety of the front of the tank, covering the glacis and lower hull, but also along the full length of the upper hull side sponsons over the tracks. The lower hull, in order to save bulk, was just the single-thickness stiff section. Likewise, the roof was a single thickness of metal as was the rear.

Distribution of armor per US Patent 3351374. The armor is concentrated on the front and upper sides, where enemy fire is most likely to be received. This is repeated on the following unit for the tank as well. Note that in this drawing the tank has only 4 wheels.

The panels inside the armor cavities were suggested as being made from a variety of possible materials, including glass-fiber or metal fabric laminated together, coated with flexible epoxy-urethane resin. Other epoxy resins, polyurethane and plastics could also be substituted. The filler material between those panels served to hold them apart and offer rigidity and was to consist of polyurethane resin too. The difference between this resin filler and the other resin used was that this filler-resin was also to contain cyclohexylstearate or dimer acid, and a lead, cadmium, or boron compound (i.e. lead oxide, cadmium oxide, boric oxide) as protection against neutron radiation. In other areas where this filler did not need to be used throughout the cavity, it was to be substituted with foam, as this was a good thermal insulator and provided buoyancy.

As an aside, Forsyth and Forsyth also considered that this armor was suitable for consideration on ships and submarines. The projected weight for both parts was just 21 to 22 tons (19.00 to 19.96 tonnes) for the steel/aluminum armor version and fro, 24 to 32 tons (21.77 to 29.03 tonnes) for the composite armored version, depending on the exact composition. The composite armor-option was a significant improvement over the original steel and aluminum option and provided the design with substantially more protection than that of the Sheridan against both kinetic energy and shaped charge munitions.

The armor arrangement as outlined for the tank but used for a submarine (left) and boat (right). Source: US Patent 3351374

Armament

As shown in the patents, there were two weapons mounted on the tank, and later, a third weapon mounted on the following unit. The tank’s weapons consisted of a single large-caliber gun of an undisclosed size in the patent, although it bears a close resemblance to a gun like that on the M551, the 152 mm. Bearing in mind the requirements from the army, as stated before, included 76 mm, 90 mm, 105 mm, and even 152 mm guns, ENTAC (to supplement a conventional gun), TOW, or POLCAT missiles, one of those would have been chosen and what is shown is too large for either the 76 mm or 90 mm guns. In their competition entry, the Forsyth brothers were clear that they planned a 155 mm gun as the primary weapon, capable of firing rocket-assisted projectiles. The secondary armament, as it appears in the patents, appears to be a cannon, but is only described as the secondary armament for anti-personnel purposes. No mention is made of the third gun at the back, which could be assumed to be a machine gun. In their competition entry, the secondary gun is confirmed as a 20 mm Hispano-Suiza HSS 820 automatic cannon in the front vehicle and the small turret at the back is confirmed to take a 7.62 mm Vulcan-type machine gun.

Side view of the complete design showing the additional rear mini-turret. Source: US Patent 3215219

Front ¾ view of the design showing the two turret hatches and the armament. Source: US Patent 3351374

Crew

The M551 was to have a crew of four, as the use of a three-man turret was seen as having value in combat. The design from Lockheed though went away from that idea and back to a three-man crew with just two in the turret. The two men, commander/gunner, and gunner/loader were seated on the left and right, respectively. The driver, lying supine to reduce the overall height of the vehicle, was located on the front left of the hull, with the engine to his right. Although being self-powered and able to operate independently of the following unit, the unit behind contained more men. Four more men in the back acted as a small armored personnel carrier team attached to the main tank and accessed it via a door at the back. They could egress the vehicle to fight or carry out tasks dismounted, and in the final patent publication’s drawings, this following unit had gained a small turret with a gun so as to provide additional firepower. As part of a platoon of such tanks, the men in the rear sections would end up being a unit 15 to 40 strong without the need for additional APC’s to follow.

Layout of automotive elements and crew from US Patent 3215219

Automotive and Suspension

The engine for this first section of the vehicle was located in the front right of the hull and centrally in the second section. It is described only as “a piston unit [conventional petrol or diesel engine] or a gas turbine” which drove an A.C. electrical generator. That electrical power was then delivered to the back of the tank (in the case of the lead unit) where traction units drove the sprockets. On the trailing unit, the same system was used except that the electrical traction units and sprockets were at the front. Steering was electro-hydraulic, able to adjust power to the tracks on each side of each section to vary the turning moment applied but also allowed for steering forces to be applied through the coupling hydraulically.

Suspension for both sections was by means of a flat band track mounted on long-pitch, large-diameter road wheels, although the designers did suggest that if tracks were not suitable that a multi-axle wheel system could be substituted instead.

Forsyth’s articulated tank concept model. Source: Armor Magazine.

One advantage of this arrangement of power with two independently powered sections connected by an articulated joint was flexibility. Either vehicle could operate completely independently or together. If one unit failed or broke, the other could push or pull it along, reducing the chances of the design becoming stuck or crippled. Further though, the independence of the electrical transmission provided additional benefits. The sections could be split and have power sent from one half to the other via cable even though they are not attached. This means that the vehicle did not have to float across waterways but instead could submerge and receive power from another tank on the bank. Once it got to the other side, it started up and sent power to the following tank in a system very similar to that adopted for the German Maus in WW2. It made loading onto aircraft for transport easier too.

Working alone or in pairs, the design was flexible enough to allow power to be sent from one vehicle or pair of vehicles to another so it can travel submerged. Source: US Patent 3215219

At just 21 to 22 tons (19.00 to 19.96 tonnes) (steel/aluminum armor version) to 24 to 32 tons (21.77 to 29.03 tonnes) (composite armored version) in total, the vehicle was air-portable and was able to split in half to easily self-load into an aircraft. Source: US Patent 3215219

Conclusion

The design from Messrs. Forsyth and Lockheed was, in many ways, ahead of its time. During the early 1960s, the concept of using composite armor was still new thinking. There were, however, serious problems to overcome. The coupling concept was not new, ideas for coupled tanks date back to 1915, and although the coupling in 1962/3 was undoubtedly better designed than the ones from 1915, it was still not a perfected technology. Lighter than the M551, this design offered increased protection and capability and the potential for improved firepower, but it was unlikely to have ever received serious consideration. By the time the first patent was filed, the US Army’s eyes were on the XM551 project, which offered a lot of what they wanted without having to use new and as of yet unproven technologies. The potential offered by this design was thus lost, it received no orders and was never built. Coupled vehicles would continue to be examined by a variety of countries for a variety of purposes, as would coupled tanks and electric drive and composite hulls. This design, however, seems to be the first design to combine all of these elements in one.

Cross-sectional view of Forsyth’s couple tank concept. Source: Armor Magazine

The tracked version of the Lockheed/Forsyth Tank

The wheeled version of the Lockheed/Forsyth Tank

These illustrations were produced by Andrei Kirushkin, funded by our Patreon campaign.

Specifications
Dimensions	1.83 m (72”) high
Mass	21 – 22 tons (19.00 – 19.95 tonnes) (aluminium/steel armor version) up to 24 and 32 tons (21.77 to 29.03 tonnes) (composite armor version) depending on armor selected.
Crew	3 (Driver, Commander/Gunner, Gunner/Loader) + 4
Propulsion	Petrol/diesel piston engine / gas turbine, with electric transmission
Range	322 to 483 km (200 – 300 miles)
Armament	155 mm main gun firing rocket-assisted projectiles (24 rounds), 20 mm Hispano-Suiza HSS 820 automatic cannon (200 rounds), 7.62 mm Vulcan-type machine gun (2500 rounds)
Armor	Steel/aluminium alloy mix 76 to 150 mm thick later changed to composite-type 76 to 150 mm thick

Sources

Armor Magazine. (July-August 1962). Tank Design Contest.
Armor Magazine. (January-February 1963). The Winning Tank Designs.
US Patent 196779 ‘ Tank Unit’, field 28th January 1963, granted 5th November 1963
US Patent 3351374 ‘Armor Construction’, filed 1st July 1963, granted 7th November 1967
US Patent 3215219 ‘Articulated Vehicle’, filed 22nd July 1963, granted 2nd November 1965
Hunnicutt, R. (1995). Sheridan: A History of the American Light Tank. Presidio Press, California
Hunnicutt, R. (1990). Abrams: A History of the American Main Battle Tank. Presidio Press, USA

Cold War US MBT Prototypes Has Own Video

120mm Gun Tank M1E1 Abrams

Post author By Andrew Hills
Post date May 9, 2020
6 Comments on 120mm Gun Tank M1E1 Abrams

United States of America (1979-1985)
Main Battle Tank – 14 Built

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

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

Experimental Model Number 1

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

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

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

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

– US Dept. of the Army, 1983

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

Blocks

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

Upgrades – Turret M1 to M1E1

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

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

Armament M1 to M1E1

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

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

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

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

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

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

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

Visual differences between the turret front and armament of the M1 compared to M1E1. Source: Mesko

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

Mobility

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

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

NBC

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

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

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

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

Other

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

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

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

Trials

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

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

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

A sequence of shots showing an M1E1 from above during tropical trials in Panama. Source: US National Archives

M1E1 Abrams with turret traversed to the rear. Source: Mesko

One of the 14 M1E1s as fitted with the XM256 120 mm smoothbore gun and other improvements, including substantial slabs of steel welded to the hull and turret front to mock up the weight of a new armor package. Source: Mesko

Pictured in 1984, this M1E1 is being evaluated. The additional plating on the front of the turret is readily apparent. Source: Zaloga

Armor M1 to M1E1

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

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

This early M1E1 during testing provides a rare view of the additional plating on both sides of the turret face. Source: Hunnicutt

Two views of two of the 14 M1E1s fitted with the XM256 120 mm smoothbore gun and other improvements, including substantial slabs of steel welded to the hull and turret front to mock up the weight of a new armor package. Note that the application of welds differs for each vehicle. Source: Mesko (right) and unknown (left)

Conclusion

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

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

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

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

Sources

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

Cold War US MBT Prototypes

Ridlon’s Main Battle Tank

United States of America (1962-1963)
Main Battle Tank – None Built

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

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

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

Suspension

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

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

Hull

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

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

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

Armor

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

Firepower

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

Automotive

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

Conclusion

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

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

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

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

Sources

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

Cold War Luxembourgish Armor Cold War US MBT Prototypes

Eischen’s Main Battle Tank

Post author By Andrew Hills
Post date February 22, 2020
No Comments on Eischen’s Main Battle Tank

United States of America/Grand Duchy of Luxembourg (1962)
Main Battle Tank – None Built

In 1962, the Cold War was at a peak, with the two great power blocks of the Soviet Union/Warsaw Pact and the United States/NATO facing off across Central Europe. By the 1960s, the Soviets had made significant strides forward in their armored vehicles and possessed both a numerical and, in many regards, a technical advantage over the NATO forces seeking to safeguard Europe.

The US was still maintaining large stocks of obsolete weapons including many from WW2 and had, by the late 1950s, realized the need for a new light tank. That program eventually led to the M551 Sheridan. When the first prototype of that vehicle was published in the summer of 1962, it appears to have spurred some further thought about a replacement or supplemental main battle tank for the US, one suitable for the perceived battlefields of Europe from 1965 to 1975. The US Armor Association issued a design competition one month after the appearance of the M551 for exactly this purpose, to design a new tank.

The designer, Sgt. Gustave L. Eischen. Source: Armor Magazine

One of the men who answered the call and submitted a design was Gustave L. Eischen. Eischen is described by the Magazine of the US Armor Association only as being from Luxemburg, with no other details. In the photo above, his uniform and cap badge appear to indicate that he was a member of the Army of Luxembourg and his rank is given as a Sergeant. The Army of Luxembourg at the time was contributing a brigade-sized force to NATO in Europe, with little prospect of beginning its own tank production.

In a newspaper article in Luxembourg published on 7th December 1962, it states that Eischen, a soldier for 8 years and a mechanic in the Luxembourg Air Force, resigned to pursue other opportunities.

Eischen’s unusual tank of 1962 showing the distinctive shape of the front and rear and the rear-turret mounted missiles. Source: Armor Magazine

Date

Eischen submitted a sketch and a model and claimed to have been working on his idea for several months prior to the competition being announced, meaning it would date to around January or February 1962 at the earliest. He had to submit it by the deadline of August 1962, so it is clearly not later than this latter date.

Technical details

The design, at first glance, is quite unusual, with four sets of tracks and a steeply angled front and rear in what could be thought of as two half-tanks joined together. This is because the design was to use a pair of air-cooled engines and two drivers, one in each half. Mounted on top of the four two-roadwheel track units, the height of the tank could be varied hydropneumatically.

Having one driver at each end allowed for the vehicle to be driven at high speed safely in either direction without having to turn around. Along with the variable height of the suspension, this would allow a good deal of off-road mobility and a range “triple that of the M60” by virtue of the several ‘special’ fuel cells arranged around the vehicle.

The shape had one more critical advantage too. It allowed for extremely good visibility from the turret both fore and aft and for the vehicle to be equally fightable in each direction.

At just 6 meters long and 3 meters wide, the vehicle would have been almost exactly the same size as the WW2-era M24 Chaffee, albeit slightly heavier at between 24 and 32 US tons (21.8 tonnes to 29 tonnes) depending on the armor thickness selected.

Side view of Eischen’s tank showing the pair of track units on each side and the diamond-shaped hull. Source: Armor Magazine

Armament

The armament was to consist of either a conventional 75 mm or 90 mm gun, which would provide excellent general-purpose firepower against vehicles and infantry support. For contact with heavier tanks, against which the gun would not be adequate, it was supplemented by a pack of ‘self-homing’ [guided anti-tank] missiles. In order to keep the silhouette as small as possible, Eischen took the unusual step of simply placing the gun and missiles at opposite ends of the turret, facing in different directions. Thus, should a heavier target need to be attacked, the gun would have to be fully rotated to fire the missile. On the drawing submitted, a machine gun, fitted to what is assumed to be the commander’s cupola on the turret roof, is also shown.

Armor

Given the low weight – less than 30 tonnes – even at its heaviest, protection would be modest. The M24 Chaffee, a comparative-sized vehicle, had conventional welded steel armor up to 38 mm thick in places. Given the additional weight of the missiles, additional driver’s station and second engine, the Eischen tank would unlikely have been able to mount armor much thicker than the M24 Chaffee. The mention of ‘special’ fuel cells though could imply that Eischen was considering the careful placement of these fuel cells to increase protection for the vehicle, but whatever details he might have provided were not included in the article concluding the competition.

Epilogue

Eischen appears to have got nowhere with his design. It won second place in the Armor competition in 1962, behind the articulated tank concept of the Forsyth brothers. His military career did not pan out either, but a lingering trace of him exists in a patent for a self-supporting element used in the manufacture of prefabricated houses filed in 1971 in Germany. There his home town is given as that of Ettelbruck in Luxembourg.

Conclusion

Eischen’s design featured the significant novelty for 1962 as hydropneumatic suspension for 4 separate track units. The two-driver idea was not particularly new as many armored cars had featured a second (backward) driver before this for the same reason, the ability to withdraw at speed. The armament offered little in the way of novelty too, a conventional 75 mm gun was by 1962 a hopeless concept for anything other than the lightest of armored targets. Even consideration of a 90 mm gun would likely have been of little use against modern Soviet tanks which is why he had added missiles. It is the missiles which are the most interesting novelty of the design as they faced backward, an unusual yet simple solution to a complex problem of mounting a missile battery on a tank.

Illustration of Eischen’s Main Battle Tank produced by Andrei Kirushkin, funded by our Patreon Campaign

Specifications
Dimensions (L-W)	6 x 3 meters
Total weight, battle-ready	21.8 tonnes – 29 tonnes)
Crew	4 (front driver, rear driver, commander, gunner)
Propulsion	x2, unknown type
Armament:	75 mm or 90 mm gun supplemented with anti-tank guided missiles, machine gun

Sources

Armor Magazine. (July-August 1962). Tank Design Contest.
Armor Magazine. (January-February 1963). The Winning Tank Designs.
Carter, D. (2015). Forging the Shield: The US Army in Europe 1951-1962. Center of Military History, US Army, Washington DC
d’Letzeburger Land 7th December 1962 ‘Ideen machen sich bezahlt Gusty Eischens Spielzeug-Panzer’
German Patent DE2135276 ‘Selbsttragendes, plattenariges wandelment’ filed 15th July 1971, granted 25th January 1973

Cold War US MBT Prototypes

90mm Gun Tank T42

United States of America (1948-1954)
Medium Tank – 6 Built

Design and Development

At a meeting at Detroit Arsenal on the 28th of September 1948, specifications outlined by the United States military for a new Medium Tank were put forward. On the 2nd of December, the designation of Medium Tank T42 was secured.
The Military’s Specifications were thus:

A weight of approximately 36 tons
Better armor protection than the M46 but equivalent armament
Main armament stabilization in elevation and azimuth
An automatic loading system
A concentric recoil system (Hollow tube around the barrel. A space-saving alternative to traditional recoil cylinders)
Blister mounted .30 Cal (7.62mm) machine gun on each side of the turret
Coaxial .50 Cal (12.7mm) and .30 Cal machine guns.

A number of these initial features were based on the Prototype Light Tank T37. This included the blister mounted machine guns. Other features included a similar chassis length with five road wheels, powerplant and transmission, mudguards/sand shields over the tracks, and a turret ring diameter of 69 inches. This was the same diameter that was introduced in 1941 with the M4.
Construction of a mock-up was approved in March 1949 and reviews of this model were held in October and December, with a number of suggestions put forward to improve the design. The similarities to the T37 began to disappear. Ground contact length was increased from 122 to 127 inches (3.09 to 3.22 meters), the turret ring was widened to 73 inches and finally, the turret mounted blister machines guns were deleted.

Hull

The hull of the T42 was a combination of two parts. The forward bow portion was a single homogeneous steel casting, while the rear was a welded assembly of steel armor plates. The two halves were welded together in the middle of the tank. The casting of the upper glacis plate was 4.0 inches (101.6 mm) thick, sloped at 60 degrees.
The T42 eliminated the archaic feature of a bow machine gun and accompanying crew member. As such, the driver was alone in the hull. Room left over by the absent crew member was taken up by a 36-round ammunition rack.

One of the first T42 Prototypes. Photo: US Archives

Mobility

The T42 did retain the engine and transmission of the T37. This consisted of the Continental AOS-895 gasoline engine (AOS: Air-cooled, Opposed, Supercharged) rated at 500 horsepower, and the General Motors CD-500 cross-drive transmission. This gave the tank a top speed of 41 mph (66 km/h). The driver operated the vehicle with the Manual Control joystick, often known as the ‘Wobble Stick’.
The tank was considered underpowered, however. Tests were mounted by placing the powerplant in the hull of an unused Medium Tank T40 chassis and running it against a late model M4A3. These tests took place at the Aberdeen Proving Ground on the 7th of November 1950. The T42 proved to be only marginally more mobile than the M4, reinforcing the opinion that the tank was underpowered.
The tank ran on a five road-wheels with the drive sprocket at the rear. There were three return rollers unevenly placed along the return of the track. The wheels were attached to torsion bar suspension.

Turret

The turret was a completely new design, but not too dissimilar to that of the T41 (M41 Walker Bulldog) in length and shape. It was completely cast in construction. The lengthy turret bustle was used to store the radio set and also housing for the ventilator fan. The turret was manned by 3 crew members; Commander, Gunner, and Loader.
The outside of the turret was dominated most noticeably by the armored housings of the stereoscopic rangefinder lenses. Also known as ‘Frog’s Eyes’, this type of gun system continued to see use after the T42 on vehicles such as the M48 Patton III and M103. Atop the turret, on the right, was the commander’s vision cupola with an AA mount for a .50 cal. machine gun. The loader’s hatch was to the right of this.

Armament

It was suggested by a British liaison officer that the Ordnance QF 20-Pounder was far superior to the 90mm Tank Gun M3A1 used on the M46 Patton. Despite its use on Britain’s own Centurion and, being a more powerful weapon, the 20-Pounder was deemed unsuitable for use on a Medium Tank by the US.
The US instead opted for a newly developed 90mm gun, the T119. This gun was a vast improvement over the M3A1. Firing it’s APDS (Armor-Piercing Discarding-Sabot) round, it could punch through 11.1 inches (282mm) of homogenous steel armor, angled at 30 degrees, at a distance of 1000 yards (914.4 meters).
The main armament was complimented by the coaxially mounted Browning M1919A4 .30 cal. (7.62mm) Machine Gun and Browning M2HB .50 cal. (12.7mm) Heavy Machine Gun.

Nomenclature Change

On the 7th of November 1950, the United States Ordnance Committee instigated a change in nomenclature for tanks in the US Military. It was decided that weight designations (Light, Medium, Heavy) were no longer suitable due to changes in the way tanks were developed and employed on the battlefield, and the varying calibers now available. The caliber of the gun replaced the weight designation. For example, the T42 changed its designation from ‘Medium Tank T42′ to ’90mm Gun Tank T42’.

The Korean Tank Panic

Six prototypes were constructed and finally delivered to the Aberdeen Proving Grounds for testing on 30th December 1950. However, by this time, the Korean War had been raging for a full six months. To put it mildly, this caused a bit of a panic among the hierarchy of the US Military, and a crash program was launched to find a suitable tank to field in the conflict. The death warrant for the T42 was signed when the US Army Field Forces (AFF) declared the tank unfit for production. This did not stop the Ordnance Department though, who continued to work on the tank in the hopes that it could yet become the US Army’s next Medium Tank. Prior to this, in November, work had begun on the T42’s replacement, designated as the 90mm Gun Tank M47. Characteristics of the vehicle were outlined in January 1951.
The immediate answer to the panic was found by returning to the current tank in service, the M46 Patton. It was found that most of the T42’s issues were with its hull and the turret was found to be perfectly serviceable. As such, a program began to mount the T42 turret on the hull of the M46.
The M46 was slightly modified to accept the new turret. This modification took the form of expanding the hulls turret ring to match the turrets at 73 inches. This combination was tested with the use of an M46 hull. This vehicle was designated the M46E1. Only one was produced for tests purposes.
To bring the M46 hull up to the requirements for the M47, the angle of the 4-inch (101.6mm) upper plate was increased to 60 Degrees from the vertical. The air filter in the upper hull front was also removed, giving a better contour to the armor profile. This configuration was accepted and serialized as the Medium Tank M47 Patton II. However, it arrived too late to serve in the Korean War. The tank was declared obsolete in 1957 in the US Military but went on to see service in the arsenal of other countries military’s. In the US, the M47 was replaced in service by the 90mm Gun Tank M48 Patton III.

An early production M47. Photo: Presidio Press

The 90mm Gun Tank T42.

The 90mm Gun Tank M47 Patton II, the combination of the T42’s turret and the hull of the M46 Patton.

The Medium Tank T69 with an Oscillating Turret mounted on the Hull of T42 Prototype vehicle no. 3.
All three illustrations are by Tank Encyclopedia’s own David Bocquelet

Further Developments

The Aberdeen trials began with automotive tests. In an effort to improve the T42’s mobility problems, the prototype vehicles sent to Aberdeen were fitted with the upgraded AOS-895-3 engine and CD-500-3 transmission. Thanks to the substitution of some steel parts with aluminum, this incarnation was 500 pounds (227 kg) lighter than its predecessor. The overall performance was improved, finally meeting the original specifications and surpassing the results of the previous test using the T40 hull. The Army Field Forces were still not impressed enough. Considering the T42 still much too underpowered, they continued to refuse its adoption. By this time, their attention had shifted to the M47 and T48 (later M48) development program.
The trials did not start well for the T42. Pilot vehicle number 1 was completely destroyed by a catastrophic fire caused by a loose pin in the final drive which tore a hole in the fuel tank. This resulted in fuel spraying over hot components of the engine. The tank was a fireball in seconds. Pilot vehicle number 2 arrived at Aberdeen in April 1951 to continue the now delayed automotive tests. This vehicle was later modified to allow the installation of a new transmission, the XT-500. This necessitated a modification the rear hull. This took the form of replacing the sloping rear hull plate with a vertical one. The XT was more efficient and had a lower production cost of the CD model, with just 60 percent of the overall part-count.

The T42 with CD Transmission on the left, and XT Transmission on the right. Note the changes to the rear of the tank. Photos: Presidio Press
Despite the deletion of the blister machine guns on the turret, developers were keen to employ extra machine guns somewhere on the vehicle to compensate for the lack of a bow mounted weapon. One solution was the mounting of machine guns on the mudguards just above the idler wheels. This took the form of an armored box. The box would contain one Browning M1919A4 machine gun, 680 rounds of .30 caliber (7.62mm) ammunition, a pneumatic charger, firing solenoid and a compressed air bottle. The system would be operated by controls in the driver’s position. The guns were fixed in traverse and elevation. Though not practical to aim, it was found that the weapons provided a good suppressing fire over an area. Further development was suggested, mostly to add a degree of traverse in the guns, but it went no further. The whole concept was later completely dropped.
During the spring of 1953, in an effort to keep the T42 project alive, a plan was formed to turn it into an option for a lighter more economical tank. Modifications planned were a steel elliptical hull and flat track suspension (track return supported by road wheels, as used on tanks such as the Soviet T-54). Had these plans materialized, the vehicle would have received the designation of 90mm Gun Tank T87, or Medium Tank T87. May 1953 marked the end of this project and the whole T42 program in general. The project was officially ended in Autumn 1954.

One of the later T42 Prototypes. Photo: Presidio Press

T69, the Only Variant

One of the original specifications for the T42 was not researched until almost a year after the tank was declared unfit for service. This specification was that an autoloader would be added when such a device was available. It was found that trying to add an autoloader in a conventional turret was impractical as the breach of the gun would have to return to a 0-degree elevation angle for it to line up after every shot. For this reason, it was decided that an oscillating turret would be the best option. Oscillating turrets are divided into two parts. A lower collar attached to the turret ring, and an upper portion with the gun fixed in place. The upper portion pivots on trunnions under hydraulic power providing the gun elevation and depression. With the gun fixed in place, the autoloader has a straight path to ram in the shells.
The new turret was mounted on the hull of T42 prototype number 3 which was modified with the XT-500 transmission. The tank received the designation of 90mm Gun Tank T69, also known as Medium Tank T69. The tank took part in a number of trials but, like the T42, it was not accepted for service. It was found that the vehicle bore no advantage over conventional designs.

The T69 at aberdeen proving grounds for evaluation. Photo: Presidio Press

Survivors

No whole T42 survives today. The only way the vehicle does survive is through the uses of its parts. A single hull survives as the T69, which currently resides in storage at National Armor and Cavalry Museum, Georgia, USA. The turret can, of course, be found all over the world where there is an M47 on display.

An article by Mark Nash

T42 Specifications
Dimensions (L-W-H)	26’9″ x 11’7″ x 9’4″ ft.in (8.1m x 3.5m x 2.8m)
Total weight, battle ready	38 tons
Crew	4 (commander, driver, loader, gunner)
Propulsion	Continental AOS-895 gasoline engine, (air-cooled six-cylinder supercharged 8.2-liter engine), 500 horsepower
Transmission	General Motors CD-500
Maximum speed	41 mph (66 km/h)
Suspensions	Torsion bars suspensions, shock absorbers
Armament	90mm Tank Gun T119 Sec: 2 x Browning M2HB .50 Cal. (12.7 mm) Heavy Machine Guns + 1 Browning M1919 .30 Cal. (7.62 mm) Machine Gun
Armor	4 in (101.6 mm)
Total production	6
For information about abbreviations check the Lexical Index

Links, Resources & Further Reading

Presidio Press, Patton: A History of the American Main Battle Tank, Volume 1, R. P. Hunnicutt
US National Archives

Cold War British MBT Prototypes Cold War Canadian Prototypes Cold War US MBT Prototypes

FV4201 Chieftain/90mm Gun Tank T95 Hybrid

Post author By Andrew Hills
Post date December 5, 2017
6 Comments on FV4201 Chieftain/90mm Gun Tank T95 Hybrid

United States of America/United Kingdom/Canada (1957-1959)
Main Battle Tank – None Built

ABC Countries

By the end of the 1950’s, tank development in both the UK and USA was becoming more streamlined with fewer outrageous ideas for atomic or super heavy monster tanks. The ‘Main Battle Tank’ concept had taken hold by 1957, inheriting the role of the medium tank. Heavy tanks were still seen, certainly in the US, as being the ones to take out the heaviest enemy armor but soon too that role was subsumed into the duties of the MBT.
The Soviets weren’t much for caring about such things and still had their own heavy tanks and well protected medium tanks which were causing consternation in the West. The Western powers lacked parity in both numbers and quality with the Soviets and both the US and UK had identified the need for a new medium tank for the 1960-1970 era. The United Kingdom, for instance, was still using the Centurion tank (a WW2 era design) and the USA, which was using the M48A2, was still developing the tank which would eventually become the M60.
In the short term, the UK would up-armor and up-gun their Centurions to meet the perceived threat of the Soviet T-55 tank until their own new tank, the FV4201, could enter production.
The FV4201 is better known as ‘The Chieftain’ and, despite being near the end of its development, many features still had not been settled on. The US equivalent program, the T95, was typical of US programs, an enormous entanglement of overlapping developments and was busily trying to encompass all of them. The project was still fairly new, however, with prototype hulls only authorised to be constructed in 1955. Thus, from 1957 to 1959, there were basically two tanks under development, the British Chieftain, which was nearing completion, and the American T95 which had only just started.
The United Kingdom, Canada, and the United States were already liaising closely in the new Cold War era on a variety of developments and tank design was not omitted from this. Work between the United States, the UK, and Canada, known as the ‘ABC’ countries (America, Britain, & Canada), had even achieved some degree of interchangeability and standardization for tank programs by 1957. Programs which had been fulfilled were standardization of the British 105mm gun, the British 120mm gun, an American version of the British 120mm gun, the American 105mm T254 and 120mm T123E6 guns, and three projects related to the FV4201 and T95.
These were:
-Mounting the FV4201 turret on the T95 chassis
-Fitting the US T208 90mm gun in the FV4201
-Mounting the US T95 turret on the FV4201 chassis
It was noted though that “in order to permit the FV 4201 turret to be mounted on the T95 hull, the U.K. consider modifying their turret ring with the T95 hull mounting surfaces”. It was agreed that “if the U.K. ring can be made interchangeable with the U.S. ring in respect to mounting surfaces on the hull, it will be possible to mount the complete turret providing major modifications are made to the turret basket”. The major modifications being that the British turret basket was too big for the T95, a smaller turret basket would be needed which would reduce significantly the amount of ammunition which could be carried. Even so, the expectation was that the T95 with a reworked 4201 turret and basket would carry at least 50 rounds of main gun ammunition. The panel reviewing the situation were adamant that all medium tanks must have ready rounds “stowed in the turret fighting compartment… in a favorable position for rapid loading of the main armament”.
That was not the end of the problems with the idea though. The turret bustle of the 4201 masked the air louvers on the T95 hull which “would undoubtedly affect the engine cooling”. One curious note records that one issue was that the driver’s periscope on the T95 hull interfered with the 4201’s gun mantlet. Exactly what this means is not clear as the FV4201 turret design was mantletless.

Guns

The British FV4201 was scheduled to enter production in 1962 with an expectation of prototypes available for trials by 1959. This new British tank meant to replace the Centurion was to mount a 120mm main gun using bagged charges. A lightened version this gun was also in development in the USA to weigh just 4156 lbs.(1885 kg). Since the initial specifications for the FV4201 were provided in the 1957 conference the design had changed slightly, improving the hull armor slope and the depression of the main gun (in a mantletless type turret) was improved from -7.5 degrees to -10 degrees.
The FV4201 turret would not be able to mount the T123E6 120mm American gun though as the weight would put the turret out of balance but it could mount the US 90mm instead. To do so would involve the use of an adaptor sleeve and the mounting surfaces of the gun but this was seen as having value for the tank in the short term.
On the other hand, the British 120mm bagged charge gun could be mounted in the T95E1 turret with only minor modifications made to the gun mount albeit at a weight increase of 1600lbs. (725.7kg). Of note here is that the T95E1 turret was the fifth turret in the American T95 program. When the T95 chassis was chosen to be common to both medium and heavy tank programs, five more chassis (for a total of 9) were ordered along with this turret. Four of those chassis went to the heavy gun tank program but as that program had no turrets ready three of the chassis were expediently fitted temporarily with existing turrets just for automotive trials. The remaining chassis got this new fifth turret and therefore was designated T95E1 to differentiate it from the others. The mention in the conference specifically for T95E1 can only, therefore, relate to this vehicle.

Medium tank guns

The 90mm T208 gun mentioned could fire the T320E60 APFSDS-T rounds at 5,200fps (1,585 mps) and defeat 5″ (127mm) of armor angled at 60 deg. at a range of 2000 yards (1828.8m). The other gun mentioned in the Tripartite Meeting on Tank Armament is the American 105mm T254 which is a lightened version of the British 105mm gun. The T254 was known to fit in the T95 turret, although “it is not planned now to install this gun in this type of turret since the installation is not ideal from the standpoint either of turret balance or turret configuration” but would be mounted on a T95 for test purposes (which would be known as T95E5). The advantage of the T254 gun was that if that gun became the standard US medium tank gun then it would be able to utilise the same ammunition as the up-gunned (105mm) British Centurion (assuming a suitable primer for the shell was selected). The Canadian contingent considered it “highly desirable that the gun and ammunition [for medium tanks] be standardized. To this end, the 90mm smooth bore can be placed in the FV4201 and the T95 turret modified to accommodate the 105mm X15 and possibly the UK 120mm bagged charge gun”.
The Canadians were anxious to see comparative firing trials between these two guns and to make an objective decision on their choice for a new medium gun tank although both were expected to exceed the requirement to defeat 120 mm of homogeneous armor plate at 60 deg. at 2000 yards which had been agreed as the standard at the Third Tripartite Conference.

Armor

Like the FV4201, the T95 was to use cast sections of armor for the nose with the sides and floor made from armor plate welded to the cast sections. This was a departure for the Americans who had already been using an all cast hull for the M48. The entire T95 turret was cast armor but the FV4201 turret was only cast in the front with the other sections made from plate armor welded on.
Overall, the T95 was expected to be a significant improvement over the M48A2’s which were already in service as “for example, the latter [M48A2] can be defeated from the direct front by the US 3000fps [914.4mps], 90-mm AP projectile on the upper hull front from 125 yards [114.3m] and on the turret front from within 1,550-yards [1,417.3m] range. The new medium gun tank, on the other hand, cannot be defeated from the front by this projectile”.
It was further theorized that the frontal armor was sufficient to defeat a theoretical Soviet 100mm AP shell traveling at 3,500 feet per second (1066.8mps) at 1,500 yards (1,371.6m) across a 60-degree arc. The armor was considered deficient, however, in terms of protection for the engine deck, sides, and rear, as well as having defective floor armor insufficient to protect from high-pressure mines. A final note on the protection for the T95 was the consideration of siliceous cored armor inside the frontal hull and turret castings although this still had not been done by this time and did not form part of the consideration for the interchangeability of the guns or turrets.

The Canadian Intervention

The Tripartite meetings of the ABC countries featured many Canadian needs. They did not class themselves as a tank producer nation, just a user, but they also had specific requirements they wanted from the tanks they were being expected to purchase. Being able to purchase either UK or US tanks effectively meant that the Canadians could be selective with what they wanted and expect that anyone who wanted to sell tanks to them would meet their demands.
For the new medium gun tank, they had agreed back in 1955 to the weight limit for this vehicle being set at 50 short (US) tons (45.36 tonnes). Both the T95 and FV4201 met this requirement, with the T95 being 20,000lbs (9,072 kg) under the weight limit.
The Canadians wanted standardization of guns, ammunition and gun mountings. They also demanded that any gun chosen had to meet the 120mm/60deg./2000 yard standard and be used in comparative firing trials. There is a small irony here that neither the FV4201 nor the T95 actually had that level of protection themselves. Further, the Canadians noted that, in comparing the designs of these tanks, the US had placed their emphasis on reducing the size of the vehicle and that while the T95 had less protection against kinetic energy ammunition than the FV4201, it did have a higher level of protection against chemical energy weapons (HEAT rounds).
In estimating the performance of the guns on offer, they determined that the UK 120mm bagged charge gun appeared to be more effective than the US 90mm smoothbore. In terms of sighting arrangements, the Canadians also preferred the British system for gun control as it was simpler, making use of a ranging machine gun compared to the US which “was still developing complex arrangements in preference to the ranging rifle system”.
In a nutshell, the Canadians wanted the best of both worlds, they wanted the hitting power of the British gun combined with the lighter, lower, more mobile US T95 to which they recorded that “the UK gun in the US tank would seem to be the logical answer. It may be technically possible to mount the 120mm bagged charge gun on the T95. With such a combination we should, for once, achieve a qualitative superiority over the Russians”.
The T95 with British gun combination favored by the Canadians was eventually effectively created by the US T95E6 mounting the 120mm T123E6 gun although the British 120mm X23E2 gun or lightened US version of it were still possible for mounting. In the meantime, while those experiments and considerations were going on, the UK had already submitted drawings to the Americans for a cost analysis for the re-engineering needed to fit the T208 and T208E9 guns in the FV4201. As it turned out, this project too came to nothing.
R.P. Hunnicutt (Abrams) records that the British 120mm gun was eventually mounted in a T96 turret in Study F of the T96 program (this being the heavy tank program) although the bagged charge was not popular with the US testers leading to the proposal to adopt a new breech and combustible case ammunition for it instead. The Americans were suitably impressed with the British 105 and 120mm guns though. So much so they made their own versions of them and “these two weapons and the original British guns were superior for tank use because of their lethality combined with lightweight, relatively short tubes, and short rounds requiring less loading space”. The only drawback of using the 120mm gun in the T95 turret was the necessity for a single loader to handle the two-piece ammunition” although a loader assist mechanism was considered to make this concern moot. Either way, the Americans elected to move on to a single piece round and modify the gun accordingly.
That modified gun was then fitted into a T95 turret in Study G (back to the medium tank program) producing a balanced gun capable of being stabilized for firing on the move.

T96 Study F turret with British 120mm bagged charge gun fitted on T95 hull. Note the use of a mantlet.Source: Abrams by Hunnicutt
T95 Study G fitted with the American version of the British 120mm gun Source: Abrams by Hunnicutt

Conclusion and one last hybrid

After the T95 program had been abandoned, the turret interchangeability concept didn’t go completely away. An initial assessment was even carried out on the XM60 as to whether it could take the British turret, the conclusion was that it was possible although it would certainly have been an odd-looking tank. The end outcome of all of the interchangeability studies is hard to gauge. The British stuck with their bagged charge gun, the American eventually chose their own gun for their own use and the Canadians were left without the tank they wanted. The option the Canadians had chosen suited their needs better than either the T95 or FV4201 could on their own: plenty of hitting power with a much more mobile vehicle. The T95 program was eventually terminated and the Canadians didn’t take Chieftains, preferring the mobility and firepower of the up-gunned Centurion instead.
The interchangeability of the guns was in itself a good idea, especially for replacement in wartime and the British turret and guns were well regarded. The interchangeability of the turrets was not easily rectified though, the Chieftain was nearly at the end of development and the British were unlikely to completely redesign the turret basket when there was no perceived market. The Canadians, after all, found the T95 turret acceptable in its own right, they just wanted the better gun. So, at the end of all this work, the overall outcome was that the interchange of T95 and FV4201 was indeed possible.
The FV4201 needed some work on the ring and basket, to take the T95 turret and the idea of mounting the T95 turret on the Chieftain was an altogether bigger task which no one was interested in trying. The report terminated discussion of the matter saying “it appears unlikely that the US T95 turret can be mounted on the UK FV4201 chassis without a major redesign of components which cannot be contemplated at this time”. As a result of the problems involved in modifying turret rings to match each other and overlapping demands for which gun was preferable, the whole affair was terminated with no prototypes completed.
The discussion does provide a real insight into just how hard it can be to design a tank to suit more than one role and customer and the idea of swapping turrets from the T95 and Chieftain tanks or even the XM60 as well as a variety of gun options remains popular if not in military circles then at least in those of modellers.

T95/FV4201 hybrid (T95 with FV4201 turret) specifications
Dimensions	Length – 426.1 inches (10.82 m) (est. based on T95E6) Width – 124 inches (3.15 m) (within the 124 inch limit imposed by the Berne International Loading Diagram) Height – >112 inches (2.84 m)
Total weight, battle ready	>32 US short tons est.
Crew	4
Propulsion	air cooled, 8 cylinder, 560 horsepower AOI-119505A with 4 speed hydraulic converter-type transmission providing at least 13.5 horsepower per ton
Suspension
Speed (road)	35 km/h est.
Range	>150 miles (241.4 km) at 17.5 mph (28.2 kph) with 230 US gallons (870.6 litres) fuel
Armament	various options
Armor	Sectional cast hull with welded plate and sectional cast turret with welded plate sides, roof and rear Hull front upper – 3.8″ @ 65 deg. (96.5mm) (to be equivalent to 4.4″ @ 60 deg. (111.8mm) which is an increase of 0.4″ (10.2mm) over the M48A2 which was 4″ at 60 deg. (101.6mm)) Hull front lower – 3.2″ to 5.5″ @ 50 deg. (81.28mm to 139.7mm) Hull sides – 1.5″ to 4″ (38.1mm to 101.6mm) Hull rear – 1″ at 0 to 20 deg. (25.4mm) Hull top – 0.8 to 1″ (20.3mm to 25.4mm) Hull floor – 0.5 to 0.7″ (12.7mm to 17.8mm) Turret – FV4201
Total production	zero
For information about abbreviations check the Lexical Index

T95E1 with British 120mm gun (the Canadian Option) specifications
Dimensions	Length – 426.1 inches (10.82 m) (est. based on T95E6) Width – 124 inches (3.15 m) (within the 124 inch limit imposed by the Berne International Loading Diagram) Height – 112 inches (2.84 m)
Total weight, battle ready	32 US short tons est.
Crew	4
Propulsion	air cooled, 8 cylinder, 560 horsepower AOI-119505A with 4 speed hydraulic converter-type transmission providing at least 13.5 horsepower per ton
Suspension
Speed (road)	35 km/h est.
Range	>150 miles (241.4 km) at 17.5 mph (28.2 kph) with 230 US gallons (870.6 litres) fuel
Armament	British 120mm bagged charge main gun with at least 50 rounds
Armor	Sectional cast hull with welded plate sides, floor and rear, and fully cast turret Hull front upper – 3.8″ @ 65 deg. (96.5mm) (to be equivalent to 4.4″ @ 60 deg. (111.8mm) which is an increase of 0.4″ (10.2mm) over the M48A2 which was 4″ at 60 deg. (101.6mm) Hull front lower – 3.2″ to 5.5″ @ 50 deg. (81.28mm to 139.7mm) Hull sides – 1.5″ to 4″ (38.1mm to 101.6mm) Hull rear – 1″ at 0 to 20 deg. (25.4mm) Hull top – 0.8 to 1″ (20.3mm to 25.4mm) Hull floor – 0.5 to 0.7″ (12.7mm to 17.8mm) Turret (T95E1) front – 7″ at 60 deg. (177.8mm)(compared to the M48A2 with just 3.7″ at 60 deg. (94mm)) Turret (T95E1) gun shield – 15″ (381mm) Turret (T95E1) sides – 3″ @ 45 deg. (76.2mm) Turret (T95E1) rear – 2″ (50.8mm)
Total production	zero
For information about abbreviations check the Lexical Index

Links, Resources & Further Reading

Report of the Tripartite Technical Conference on Tank Armament – October 1957
Abrams – Hunnicutt
Fourth Tripartite Conference on Armour – October 1957
Tank Factory – William Suttie

T95 hull with XM60 Turret and standard 90mm Gun.

The hull of T95 Pilot No. 2 with 90mm Gun T208.

FV4201 hull with T96 Study F turret and British 120mm bagged-charge gun, without fume extractor.

T95 hull with an impression of an Americanised FV4201 Turret with M48/M60 style commanders cupola and 120mm gun with fume extractor.

T95 Hull with the standard FV4201 Chieftain turret and 120mm gun.

All illustrations are by Tank Encyclopedia’s own David Bocquelet.

Cold War US MBT Prototypes

90mm Gun Tank T69

United States of America (1951-1958)
Medium Tank – 1 Built

In the early 1950s, the United States Military began a design program to develop tanks that would replace those currently in service. The faithful M4 Sherman had begun to show its age and was in the process of being replaced by the M26 Pershing and the upgraded M46 Patton.
At their core, however, these tanks were still very much vehicles of World War II era and did not make use of newer technologies that had begun to appear. One of the tanks to spring from the design program was the Medium Tank T42. This tank would form the basis of the T69 project.
The unique feature of the T69 among other medium tanks then in development was its oscillating turret and autoloading system. The T69 project followed on from the T71 Light Tank project, which featured a 76mm autoloading gun in an oscillating turret. It also ran parallel to the 120mm armed T57 and the 155 mm armed T58 Heavy Tank projects. Both of which also featured autoloading systems and oscillating turrets. These two were based on the hull of the M103 Heavy Tank.

The Medium Tank T69, with an Oscillating turret, based on the hull of the T42 Medium. Photo: Presidio Press

The Medium Tank T42

The T42 was originally designed to replace the M46 Patton. Starting life in 1948, the T42 was based on the T37 light tank prototype, but had increased armor protection and carried a T139 90mm gun (which would later be serialized as the 90mm Tank Gun M41) in a brand new turret. It did, however, retain the same basic dimensions and the five road-wheel running gear.

The T42 prototype. Photo: US Archives
The T42, to the worry of the US Military, was still halfway through development when the Korean War Commenced in June 1950. This gave rise to the infamous “Korean Tank Panic”. As a quick solution to this problem, it was decided to take the turret of the T42 and mount it on the M46 hull. This spawned the Medium Tank M47 Patton II.
The T42 itself would never make it to full-scale production, having never met all of the Military’s needs and expectations. A few of the tanks would be kept for experimentation and further development. This led to its use as the base hull for the T69.

Birth of the T69

The T69 was born out of the idea from the United States Ordnance Committee that an automatic loading system would be added to the T42’s turret should one be designed and become available. Preliminary experiments with a loading system inside this turret were not successful due to the limited space and the need to line up the breach with the loading system after every shot.
Further studies by the Rheem Manufacturing Company found that it would indeed be feasible to mate the T139 90mm gun with an autoloader if the equipment was mounted in an oscillating turret. Oscillating turrets, made famous by the French and their AMX-13, were a new feature at this time. These turrets have a fixed gun in a two-part turret. The lower half, or ‘collar’, is connected to the turret ring and provides horizontal rotation. The upper part, or ‘body’, carries the gun moving up and down on a set of trunnions providing vertical traverse. Turrets of this design allowed the use of autoloader mechanisms as the gun was fixed in place, meaning the loader did not have to be re-aligned with the breach after every shot.

Profile shot of the T69. Photo: US Archives
A new contract was drafted with Rheem who then proceeded to draw up plans and prepare mockups of the turret and loading system. Work began on the turret in summer 1951. However, there were lengthy delays due to the late arrival of equipment. A total of six different designs for the turret were evaluated by APG (Aberdeen Proving Grounds) and tested by personnel supplied by the AFF (Army Field Forces) before one was selected. A number of turrets for ballistic tests were then built for APG to test the armor protection. Only after this would development finally continue in the summer of 1955.
The turret was mounted on the second T42 pilot vehicle modified to carry the XT-500 transmission. This combination was then designated the 90mm Gun Tank T69, otherwise known as Medium Tank T69.

Hull

The hull of the tank was made up of two parts. The front half was a long rounded casting of steel homogeneous armor, it was 4 inches (101.6 mm) thick and angled at 60 degrees. The rear was welded steel armor plate. The two halves were welded together in the center.

Engine

The T42 hull was powered by the Continental AOS 395 gasoline engine, (air-cooled six-cylinder supercharged 8.2-liter engine) rated at 500 horsepower. This ran through a General Motors CO-500 cross-drive transmission, later upgraded to the XT-500 (this required changes to rear of the engine compartment, resulting in a vertical rear plate). Together, this gave the vehicle a top speed of about 41 mph (66 km/h). This engine was retained for the T69. The driver’s position was located at the front left of the hull with an ammunition rack to his right. The driver steered the vehicle via the Manual Control Stick, often known as the “Wobble Stick”. The Manual Control was a single joystick that controlled left and right movement, as well as controlling forward and backward speeds.

Turret

The body of the turret was a single cast piece with the 90mm gun protruding from a long ‘nose’. The angles of the casting provided numerous deflective surfaces against incoming rounds. This body was attached to a fully cast collar by trunnions, forming the fulcrum point of elevation and depression. Maximum elevation was 15 degrees, maximum depression was 9 degrees. This motion was actuated by a hydraulically powered mechanism, though should it fail manual operation was possible. The collar was then attached to the 73-inch turret ring.
Turret crew consisted of the Gunner, Loader, and Commander. The Loader sat to the left of the gun, with the gunner on it’s right. The Commander was situated at the right rear of the turret underneath a rotating vision cupola.

Another profile shot of the T69. In this photo, the turret is partially raised to about half of its maximum elevation, and the roof is open. Note the hydraulic bar propping up the roof. Photo: Presidio Press
Access into the turret was rather easy. There was a hatch on the left of the turret roof for the loader, and another atop the Commander’s cupola at the rear right. The traditional hatches in the turret roof were not the only point of entry, however. If needed, the entire turret roof had the ability to raise up via hydraulics and could rise to almost a full 90 degrees. This allowed full access to the interior of the turret, easy removal of the gun and loading system, and quick ammunition resupply. In case of emergency, it also allowed for a quick exit of the turret. This was operated by a control in the Loader’s position.
Other features on the turret consist of an AA mount for a Browning M2HB .50 Cal. (12.7mm) Heavy Machine gun on the commander’s cupola and a ventilator in the left rear. On each side of the turret, positioned just above the fulcrum point were the ‘Frog’s Eyes’, the armored housings for the lenses of the stereoscopic rangefinder. The same can be found on the M47, M48 and so on.

An interior photo of the T69s turret taken recently at the NACM. 1: Gunners position. 2: Escape hatch. 3: 90mm Gun. 4: Recoil guard. 5: Ammunition cyylinder. 6: Ramming and extraction system. Photo: Rob Cogan.

Links, Resources & Further Reading

Presidio Press, Patton: A History of the American Main Battle Tank, Volume 1, R. P. Hunicutt
An original government report on the T69, Read HERE.
National Armor and Cavalry Museum (NACM)
NACM Curator, Rob Cogan

Illustration of the T69 Medium Tank prototype by Tank Encyclopedia’s own David Bocquelet. The color is speculative as there are no known original colored photos. As such, the standard US Olive Drab paint scheme was chosen.

Armament

The T69 was armed with the T178 90mm gun. This gun was essentially the same as the T139 but was mounted upside-down. This meant that the vertically sliding breach slid up towards the turret roof instead of down towards the floor, avoiding collision with the loading mechanism. The mounting lugs were also modified so that the gun’s concentric recoil mechanism (hollow tube around the barrel. A space-saving alternative to traditional recoil cylinders) could be mounted in the forward part of the turret, in the nose. There was a fume extractor towards the muzzle of the gun, just behind the muzzle-break. This was a relatively new feature on tanks at the time. Firing an AP (Armor Piercing) shell, the gun could penetrate 6.2 inches (157.48 mm) of armor at 1,000 yards. A coaxial Browning M1919 .30 Cal. (7.62mm) Machine Gun was mounted on the left of the main armament. When not in action, the turret would be traversed almost fully to the rear. The gun would then be placed in a travel lock mounted on the left rear of the engine deck.

A head-on shot of the T69, showing the 90mm gun, coaxial .30 cal (7.62mm) mg to its left, and the .50 cal (12.7mm) on the commander’s hatch. Photo: Presidio Press.

Autoloader

The T178 gun was fed by an 8-round autoloader mechanism. The system was mounted longitudinally on the centerline of the turret. It consisted of a magazine with an integral ramming system. The magazine took the form of a conical 8-tube revolving cylinder, like a scaled-up version of something found on a Smith & Wesson Revolver for example. The chambers of the cylinder were reloaded manually by the Loader and could be loaded with up to three different types of ammunition. AP (Armor Piercing), HEAT (High-Explosive Anti-Tank) or HE (High-Explosive) for example. The gunner could select which ammunition type he needs to fire via a control panel in his position.

A cross-section of the T69’s turret showing the autoloading apparatus. Photo: Presidio Press
When engaged, the cylinder was lifted into line with the breach, the hydraulic rammer then pushed the round forward into the breach. Upon withdrawal of the rammer, the cylinder indexed (rotated) forwards one chamber. The cylinder assembly then dropped back down to its stationary ready position low in the turret. Once fired, the empty shell was then passed along a chute to an ejection port in the turret bustle that automatically opened upon recoil of the gun. Once the shell was clear, the port automatically closed when the gun returns to battery (recovers from recoil). The rate of fire could be as fast as 33 rounds per minute. This was when firing just one ammunition type when interchanging between various types, rate of fire was reduced to 18 rounds per minute.
As well as the eight rounds in the cylinder, 32 rounds were held in the bow to the right of the driver. In the T42, this rack held 36 rounds. It was found, however, there was little clearance between the autoloading assembly and the turret ring for the loader to have access to this row of four extra rounds. It was the responsibility of the Loader to replenish the Cylinder when all rounds were spent.

A rear view of the T69 with the turret open. Note the shell ejection port in the turret bustle. Photo: Presidio Press

Fate

The T69 was tested at Aberdeen Proving Grounds from June 1955 to April 1956. The tests were dogged by a high rate of component failure which prevented in-depth study of the automatic loading system and operation of the oscillating turret. The tank was deemed unsatisfactory for service, but various tests on the vehicle would continue. Lessons learned would pave the way for future technologies and developments. The T69 Project was finally officially terminated February 11th, 1958.
The T69 was not the last experiment with oscillating turrets and autoloaders by the US Military. The project would be followed by the T54. Not to be confused with the infamous Soviet T-54, these were a series of prototypes based on the M48 Patton III hull. They were intended as a means to develop a turret for the M48 that could carry the 105mm Tank Gun T140. A variant of this project, the T54E1, carried the gun in an oscillating turret and used an autoloading system.

A photo taken in the early 1980s showing the tank at the Aberdeen Proving Grounds. Photo: preservedtanks.com
The T69 did survive, however. It was preserved at the Aberdeen Proving Grounds for many years, but it has since been removed from the site with the closure of the museum in late 2010. It was moved to Fort Benning and is currently a part of the collection of the National Armor and Cavalry Museum (NACM), Georgia, USA. The museum will open to the public in a few years. Recently, the tank was stripped of its old weathered paint given a fresh coat of protective Red-Oxide primer. In late 2017, the vehicle was given a fresh coat of Olive Drab paint.

The repainted T69 at the National Armor and Cavalry Museum. First picture shows it in the red oxide, the second shows it in its new paint job. Photos: NACM and Rob Cogan

An article by Mark Nash

T69 Specifications
Dimensions (L-W-H)	26’9″ x 11’7″ x 9’4″ ft.in (8.1m x 3.5m x 2.8m)
Total weight, battle ready	38 tons (76,000 lbs)
Crew	4 (commander, driver, loader, gunner)
Propulsion	Continental AOS 395 gasoline engine, (air-cooled six-cylinder supercharged 8.2-liter engine), 500 horsepower
Transmission	General Motors XT-500
Maximum speed	41 mph (66 km/h)
Suspensions	Torsion bars suspensions, shock absorbers
Armament	90mm Tank Gun T178 Sec: 1 x Browning M2HB .50 Cal. (12.7 mm) Heavy Machine Gun + 1 Browning M1919 .30 Cal. (7.62 mm) Machine Gun
Armor	4 in (101.6 mm)
Total production	1
For information about abbreviations check the Lexical Index

EDMBT specifications

M-70 Specifications

Specifications

Specifications

Specifications

Specifications

T42 Specifications

T95/FV4201 hybrid (T95 with FV4201 turret) specifications

T95E1 with British 120mm gun (the Canadian Option) specifications

T69 Specifications

40-ton Electric Drive Main Battle Tank (E.D.M.B.T.)

M-70 Main Battle Tank

Lockheed/Forsyth Tank

120mm Gun Tank M1E1 Abrams

Ridlon’s Main Battle Tank

Eischen’s Main Battle Tank

90mm Gun Tank T42

FV4201 Chieftain/90mm Gun Tank T95 Hybrid

90mm Gun Tank T69

United States of America (1984-1987) MBT – Models Only

Why Electric Drive?

Study Concepts

Baseline Vehicle Description

40-ton (36.3 tonnes) vehicle Concepts

Garret Concept I-3 40-ton (36.3 tonnes) Application

Conclusion

Sources

EDMBT specifications

United States of America (1962-1963) Main Battle Tank – None Built

Layout

Armament

Crew

Armor

Suspension

Conclusion

Sources

M-70 Specifications

United States of America (1962-1967) Articulated Light Tank – None Built

Designers

The Need For a Light Tank

Basic Layout

Armor

Armament

Crew

Automotive and Suspension

Conclusion

Specifications

Sources

United States of America (1979-1985) Main Battle Tank – 14 Built

Experimental Model Number 1

Blocks

Upgrades – Turret M1 to M1E1

Armament M1 to M1E1

Mobility

NBC

Other

Trials

Armor M1 to M1E1

Conclusion

Specifications

Sources

United States of America (1962-1963) Main Battle Tank – None Built

Suspension

Hull

Armor

Firepower

Automotive

Conclusion

Specifications

Sources

United States of America/Grand Duchy of Luxembourg (1962) Main Battle Tank – None Built

Date

Technical details

Armament

Armor

Epilogue

Conclusion

Specifications

Sources

United States of America (1948-1954) Medium Tank – 6 Built

Design and Development

Hull

Mobility

Turret

Armament

Nomenclature Change

The Korean Tank Panic

Further Developments

T69, the Only Variant

Survivors

United States of America (1984-1987)
MBT – Models Only

United States of America (1962-1963)
Main Battle Tank – None Built

United States of America (1962-1967)
Articulated Light Tank – None Built

United States of America (1979-1985)
Main Battle Tank – 14 Built

United States of America (1962-1963)
Main Battle Tank – None Built

United States of America/Grand Duchy of Luxembourg (1962)
Main Battle Tank – None Built

United States of America (1948-1954)
Medium Tank – 6 Built

United States of America/United Kingdom/Canada (1957-1959)
Main Battle Tank – None Built

United States of America (1951-1958)
Medium Tank – 1 Built