The Assault Tank T14 was a more heavily armoured version of the Sherman, designed to lead attacks.
Work on the T14 came about largely because of British interest in the idea of the assault tank. At a meeting between the Chief of Ordnance, the Aberdeen Proving Ground and the British Tank Mission both countries agreed to produce two pilot assault tanks. In May 1942 the Ordnance Committee issued the specifications for the American vehicle, and the UK issued a requirement for 8,500 assault tanks. At this point the US Armored Force had no interest in the idea.
The Aberdeen Proving Ground drew up the preliminary designs by June 1942, and the job was then passed onto the American Locomotive Company. The resulting vehicle used some elements from the Medium Tank M4 Sherman, but much of the tank was either new or came from other vehicles.
The M4 provided the drive train, and the cast one piece nose. Power was provided by the Ford GAZ V-8 engine, similar to the engine used in the M4A3, one of the main US combat versions of the M4. Enough space was provided for the Ford V-12 that the GAZ was based on.
Suspension came from the Heavy Tank M6, and used three bogies on each side. Each bogie carried two 18in wheels, and used horizontal volute springs. The T14 also used the 25.75in wide tracks of the M6.
The hull used welded construction, and had a flat top, with the turret mounted at about the mid-point. The side armour was sloped at 30 degrees at the top and was 2in thick. The suspension was protected by 0.5in thick side plates. The lower side armour (inside the suspension) was 2.5in thick. The front armour ranged from 2in-4in, the rear armour was 2in thick. The cast turret had sloped sides and front, with 3in of frontal armour and 4in at the side and rear.
The T14 prototype carried the standard 75mm gun M3, as used on the Sherman. Plans were also drawn up to use the 105mm howitzer.
A wooden mock-up of the T14 was completed in November 1942, detailed design work finished in April 1943 and the first pilot was delivered in July 1943. The T14 didn't impress in tests. Mobility was poor, the tracks tended to come off and were difficult to reach behind their armoured skirts. Overall maintenance was difficult.
A plan had been put in place for the production of 250 T14s per month, at the General American Transportation Company, but these were cancelled before any had been built. One of the pilots did go to Britain, and is now at the Tank Museum, Bovington, but by this point British interest in the design had faded, and the T14 didn’t enter production. One assault tank based on the Sherman did enter production, the Assault Tank M4A3E2, but this was a much less complex adaptation.