10 January 1942. Grand Blanc, Michigan. USA.
Fisher Body, a subsidiary of General Motors, was one of the many firms that were responding to the President’s order to double the tank production schedule from 1000 to 2000 per month. The new plant was going to be 452000 square feet, some eight American football fields. Modelled on the Detroit Arsenal, Fisher’s plant would begin producing M4 medium tanks in July. The Pacific Car & Foundry, Ford and Federal Machine & Welder were the other companies added to the already impressive list. By the time the M3 production switched to the M4 at some convenient time in early 1942, and full production of the M4 begun, eleven plants would be building the new tanks.
The Medium tank T6 wooden mock-up had been approved by the Armored Force Board in May 1941, the pilot model had been completed at the Aberdeen Proving Ground in September 1941. The T6 was standardised as the Medium Tank M4 in October. The pilot model was being built by Lima Locomotive works, and would be ready for full testing in February. Pressed Steel and Pacific Car & Foundry, along with Lima would begin full production in March. These three companies would be using cast hulls, and the engines would be the Continental R-975 engine and the same bogies as the M3 Medium tank. The gun was to be the M2 75mm, with counterweights, until enough M3 75mm guns were available.
Once Fisher Body’s new factory was up and running, they would be making the M4A2 model of the tank. The main difference was having twin General Motors 6-71 diesel engines, Continental couldn’t provide enough of the radial engines for all the M4s planned. Other engine types would also have to sourced to meet the production numbers. Some tanks would have welded rather than cast armour, which would create yet another subtype.
Despite advice from the British, the first models (known as M4A1) would also have two fixed machine guns in the front hull. These would be of limited use and compromised the armour protection of the hull. The British had also asked for thicker armour, the 50mm in the hull was considered too vulnerable, some of the turret protection of 75mm was much better, but there was always going to be the problem of increasing armour would increase weight, making the engine struggle to keep up the desired speed on roads of around 25mph, about 15mph off road. The British also had requested that the Lend Lease models destined for the UK would have protected ammunition stowage. This was standard on the Valiant tank that the Americans had studied to help with the turret mechanism.
The first M4A1 built at the Lima plant would be handed over to the US Army, the second would be shipped to Britain for thorough testing. Members of the British Tank Mission, led by Major-General Douglas Pratt (Armoured Fighting Vehicles British Army Staff Washington) had attended the ground-breaking and was amused by the American alliteration of the Grand Blanc Tank Plant. In terms of size, efficiency and the speed of building a factory and starting production within such a short period of time, Fisher’s was a marvel. Pratt was better used to the smaller tank shops in Britain where sixty tanks per month was considered ‘big’. Here, once production was in full swing 180 tanks were expected to roll off the production line per month, that was enough tanks for a new British Armoured Brigade every month! It was no surprise to Pratt and his colleagues that the Americans weren't really prepared to listen to what the British had to say. The sheer muscle of American industry producing thousands of tanks per month was a confirmation to Pratt that Hitler and Tojo didn’t have a clue what was about to be unleashed upon them.