The period starting at the end of the Second World War and going into the new postwar world was a very busy time for US tank design despite the slashing of many programs and budgets from March 1945 onward. The scale of US experiments makes it hard to separate out one design from another as there was so much overlap between armor requirements, speed, and firepower. There was also the switch in the perceived enemy, no longer were tanks being conceptualized to fight the Germans or even the Japanese but instead to fight the armor of the Soviet Union. The enormous number of ideas, concepts, and proposals is simply overwhelming but one project stands out as an example of one of the less extreme ideas.
The ‘Improved Medium Tank’ may date back as far as September 1944 according to ‘Faint Praise’ by Charles Baily. This is based on the date given for the artist’s impression which is the only known image of what this vehicle would look like and which is used into 1945 for the project. The paperwork relating to the design is a little later though and the whole concept stems from the need to develop a new medium tank to replace the older obsolete M4 series. The replacement for the M4 was not a straightforward process though and the Army Ground Force (AGF) had failed to get the T25 Medium Tank into production and they weren’t satisfied with the suggestion from the Ordnance Department for the T20 series tank either. This meant that they did not have a replacement medium tank in development for the army (the T26 was still classed as a ‘heavy tank’ at this time). Clearly, this was an unacceptable situation and the result of this medium tank deficiency was that the AGF simply created their own requirement for a new medium tank instead. This new medium tank can, therefore, be called ‘The AGF Medium Tank’ and a look at the requirements gives a good impression that the AGF really had paid a lot of attention to the needs of combat and of tank crews. They also seem to have allowed some unrealistic expectations to creep into their thought process too as will be apparent in a review of the statistics for the vehicle.
Improved Medium Tank from artists impression 28th September 1944.
The AGF submitted the specification for their 45 ton medium tank on the 6th of December 1944. It was almost immediately rejected on the basis that the specifications were expected to result in a tank of 60 tons because of “increased bulk requirements due to the demand for increased power, cruising range and larger diameter turret ring…” and was even called “amateurish” but it could not simply be dismissed without some kind of study being conducted. The Ordnance Department, busy with their own program, would not conduct a study of a rival product.
It was on the 2nd January 1945 that the Army Ground Force met in Washington D.C. to finalise their ideas. Their report was ready on the 20th June 1945, just after the war in Europe had ended. Among other vehicles, the report specified that the new medium tank had to be in the 45 ton class. Exactly what the differences between this concept and the initial one are is not entirely clear but some hints can be gleaned from the specifications.
The purpose of the AGF 45 ton Improved Medium Tank was simple; it was to be the “primary weapon for tank units, both in armored divisions and separate tank battalions”. The specified fully laden combat weight of this tank was listed as 90,000lbs, which is 40,823kg, just over 40 metric tonnes or 45 US short tons. No dimensions are listed explicitly except width which was to be at most 134 inches (3.4 metres) due to transport requirements with height and width only to be the “minimum consistent with efficient construction and design”.
Protection was to be from rolled homogenous armor and “all armor should be as heavy as possible consistent with weight limitations, any reduction in armor thickness should be proportional” with a minimum of 6″ (152.4mm) for the hull front although 8″ (203.2mm) was desired. Just to illustrate, the minimum requirement was the same thickness as that of the frontal glacis of the Königstiger! The hull sides were to be 3″ (76.2mm) thick on the sponsons around the crew compartment, down to just 1.5″ (38.1mm) thick over the engine and the lower half of the hull sides over the crew compartment was to be just 2″ (50.8mm) thick. The hull rear was also to be 1.5″ (38.1mm) thick, with a 1″ (25.4mm) thick floor under the crew compartment and just ½” (12.7mm) thick under the engine. The hull roof was to be 2″ (50.8mm) thick over the crew compartment down to ¾” (19mm) thick over the rear of the hull.
The turret, which was to have a turret ring with a diameter of at most 80″ (2032mm), was to match the frontal protection with 6″ (or preferably 8”) of armor including the mantlet, 3″ (76.2mm) thick at the sides, 2.5″ (63.5mm) thick at the rear and a 1″ (25.4mm) thick roof.
Surprisingly for a future medium tank, this vehicle was selected to have a main gun of not more than 3″ (76.2mm) caliber stating that the gun must be “specifically designed in view of the space limitation in tanks.” Specific requirements for the gun were that it was to have the smallest possible chamber size, a compact recoil system with a short recoil stroke, and the shortest possible distance from the trunnion to the semi-automatic breech block as possible.
The single piece ammunition for the gun was to achieve the specified performance of being able to defeat enemy armor up to 8″ (203.2mm) thick at an angle of 30 degrees at a range of 1000 yards (915 m). The firing though would have to cause as little smoke as possible as there was a problem with target obscuration after firing and it had to not cause excessive barrel wear. The dimensions for the ammunition were specified to not exceed 35 lbs in weight (15.9kg) or be longer than 30″ (762mm) inches in length with a total length of 33″ (832.8mm) being the absolute limit.
The penetration requirement of just over 200mm was certainly not impossible with the use of special ammunition like Armor Piercing Discarding Sabot (APDS). In terms of shell size, for comparison, the APDS shell for the British 17pdr gun was just an inch longer at 34″ and could achieve 200mm of penetration, just under the requirements made. Some development might have been needed but effectively the AGF was looking at a gun not that different from the British 17 pounder firing ‘special’ AP ammunition.
The coaxial weapon choices give a little insight into the designer’s mindset as it includes several machine guns and a flamethrower. First, there were to be 2 coaxial machine guns, one .50 caliber and one .30 caliber both of which could be fired independently or together with the main gun, which was also to have a separate electrical firing system installed. Two more .30 caliber machine guns were to be installed “symmetrically located outside the turret in ballistic blisters so mounted as to fire coaxially with the main weapon” and yet another .30 cal fitted in the hull fireable by the driver. Not content with this array of machine guns the AGF stated that “consideration to be given to the mounting of bow machine guns or guns in remote-controlled ballistic blisters” and the artist’s impression seems to indicate the presence of two machine gun blisters on the front of the machine. One final machine gun was a .50 calibre anti-aircraft weapon to be installed on the turret roof fireable remotely by the tank commander and capable of being directed at ground targets if needed, presumably because the other 6 machine guns weren’t sufficient.
At least 6 smoke projectors in an armored housing were to be fitted to the outside of the tank fireable from inside and able to go out to 200 yards (183m). The final offensive weaponry was in the form of a swivel type flamethrower on the roof of the bow gunner’s compartment provided with traverse within the limits of his visibility and with a flame burst of not less than 30 seconds up to 1 minute. For defense, it is specified that fragmentation grenades must be deployable by crew to a range of 10 yards (9.14m) around the sides and rear of the tank without opening any hatches.
No less than 85 rounds of main gun ammunition were to be carried, along with at least 600 rounds for each .50 calibre machine gun, and 2500 rounds for each .30 calibre machine gun, 24 grenades, 6 smoke bombs, and at least 600 rounds of .45 calibre ammunition complete the logistical insight into ammunition supply.
The main gun was to be stabilized horizontally and vertically for firing on the move. It was also specified that the coaxial weapons had to be stabilized at least 90% of the time as well. A built-in 10x rangefinder linked to the gun was to be fitted along with a tank commander’s x4 or x6 sight with “provision… to lay the gunner on the target through the agency of the rangefinder”.
Another feature was that “the tank commander shall be provided with elevation and traverse controls that will follow the same response curves and shall override the gunner’s controls”. Finally, an auxiliary sight adjustable from x3 to x8 power and marked with various graduations to accommodate different ballistics of various ammunition types was used along with a 7 x 50 periscopic binocular sight on a rotatable plate for the tank commander. There was to be an elevation quadrant on the gun mount for the gunner, and all of this was supposed to be ‘rugged, simple, and accurate’ and unaffected by engine vibration.
The 360-degree rotatable turret would be fully balanced and fitted with both a power and a hand traverse with not more than 200 lb.ft. (271.16 N.m) of torque required to traverse it. Other issues for the turret were that it was to be sealed from weather and, like the hull, sealed from harmful gasses. Armored covering would cover the vision openings and the design shaped in such a way as to minimise ricochets from the turret into the roof of the tank. During travel, a sturdy travel lock would be used to secure the main gun.
The improved Medium Tank was to be fitted with power steering and independently sprung wheels with shock absorbers over which would run a center-guide type track with a rubber bogie surface and integral grousers. The track lifetime had to be at least 3000 miles. It was specified that it also had to be suitable for climbing a 60% grade slope in damp clay.
The engine was to be a multifuel engine which would have to be developed specifically for it and capable of running on standard military fuel, oil and lubricants. It had to produce at least 20 horsepower per ton and cause minimal vibrations. Ease of maintenance was important along with a 5000 miles (8047 km) / 500 hours overhaul interval. The transmission would be either an “infinite ratio type” or fully automatic and if a clutch was to be used it had to have a long life and be free from dust. Whichever system was used, it had to have a high reverse speed.
Twenty horsepower per ton with a weight at 45 tons was implying an engine producing 900hp and such an engine did not exist for them, the engine in the 46 ton M26 Pershing, for example, was just 500hp.
As if the other requirements for the engine were not unrealistic enough the tank was also to have enough fuel for a cruising range of at least 100 miles (161 km) and the expectation was for a top speed on the road of not less than 20 mph (32 kph) sustained.
In terms of stowage, this new tank would carry not less than 3 days of crew rations, a minimum of 5 gallons (18.9 litres) of drinking water (preferably 10 gallons / 37.9 litres) along with standard pioneer tools, spare parts and a 12 unit first aid kit in an armored external box.
The radio would be fitted as specified by Army doctrine along with a fixed fire extinguisher system and a positive pressure ventilation system for the crew. In the event of a failure of this system a door could be opened from the crew compartment to the engine to draw in air through the hatches for the crew that way.
Easily openable hatches were to be wide enough for crew in winter uniforms, seats to be adjustable, non-skid surfaces were to be used inside along with no sharp corners or projections. All instruments had to be operable while wearing gloves, and an escape hatch was to be fitted in the hull floor. Other features would include a red/white interior light, illuminated instrument panels, and the maximum use of alloys to save weight.
Exterior lighting was to be exactly that of the M4 series and the tank was to be easily towable with a temperature operating range from -10F (-23.3 C) to +120F (48.9 C) and wind speed up to 40mph. With winterization the vehicle would be suitable to operate down to -40F (-40 C).
Artist’s impression of the ‘Improved Medium Tank’ from AGF Report June 1945. The relevance of the square squares drawn on next to each machine gun is not known.
Looking at the specifications for the tank it is easy to see that a considerable amount of experience has gone into them. Crew comfort from seats to avoiding sharp corners and the use of gloves etc. all feature and yet still the AGF managed to add in a simply ridiculous amount of pointless items such as the superfluous machine guns scattered around the machine. The 3” gun specified might have been suitable for 1944 when it was first being considered but it was already going to be outdated by the time it could have entered production if it was approved.
Whatever the thinking was it was redundant. A new board under General Stilwell had convened in November 1945, known officially as the War Department Equipment Review Board (unofficially known as the Stilwell Board), to consider many of the same issues the AGF had. By the 19th January 1946, the Stilwell Board completed its own report and the idea for this tank was effectively dead. Any final hints of it completely disappeared by December 1950 when the requirements changed with the release of the Army Equipment Development Guide and the Army moved in a different direction with its medium tanks. The AGF’s Improved Medium Tank was consigned to history and mostly forgotten, the last grasp at a WW2 tank design.
AGF Improved Medium Tank specifications
|Dimensions||length not specified, width 3.4m, height – not specified|
|Total weight, battle ready||40,823kg (90,000lbs.) est.|
|Propulsion||20 horsepower per ton, ~900hp desired|
|Speed (road)||Not less than 32 km/h (20 mph)|
|Range||Not less than 161 km (100 mi)|
|Armament||3″ (76.2mm) gun capable of penetrating 8″ (203.2mm) at 30 deg. at 1000 yds. (914.4m) with at least 85 rounds|
Coaxial .50 calibre machine gun with at least 600 rounds
Coaxial .30 calibre machine gun with at least 2500 rounds
Symmetrically mounted .30 calibre blister mounted external machine guns with at least 2500 rounds each.
One .50 calibre AA machine gun with at least 600 rounds.
At least one .30 calibre hull machine gun (possibly two in blisters) with at least 2500 rounds each.
Smoke projectors with 6 bombs.
24 fragmentation grenades.
At least 600 rounds of .45 calibre ammunition for crew weapons.
Swivel type flamethrower with 30 to 60 seconds of fuel.
|Armor||Hull front – 6″ (152.4mm) min, 8″ (203.2mm) desired|
Hull sides upper – 3″ (76.2mm) on sponsons around fighting compartment
Hull side lower – at least 2″ (50.8mm) around fighting compartment
Hull sides behind FC – 1.5″ (38.1mm)
Hull rear 1.5″ (38.1mm)
Hull top front over FC – 2″ (50.8mm)
Hull top rear ¾” (19mm)
Hull bottom front under FC – 1″ (25.4mm)
Hull bottom rear ½” (12.7mm)
Turret front 6″ min., 8″ desired including mantlet
Turret sides 3″ (76.2mm)
Turret rear 2.5″ (63.4mm)
Turret top 1″(25.4mm)
|For information about abbreviations check the Lexical Index|
Links, Resources & Further Reading
Patton – R.P. Hunnicutt
Firepower – R.P. Hunnicutt
Army Ground Forces Equipment Review – June 1945
Report of the Army Equipment Board – 1945
Faint Praise: American Tanks and Tank Destroyers during World War II – C.M. Baily
An impression of AGF’s ‘Improved Medium Tank’ by Tank Encyclopedia’s own David Bocquelet.