With events in Europe in 1940, the Army realized the M2 was inadequate and the decision was made to modernize it.11,12 A new design with thicker armor was standardized on July 5, 1940.6,7 Production started in March 1941 at the American Car & Foundry.7 It was based on the M2A4, but had thicker armor that was homogeneous rolled and the idler wheel was placed on the ground to act as another road wheel to help distribute the weight.1,6,10
Initially the engine was the Continental but shortages caused it to be replaced by the Guiberson T-1020 diesel, and fitted into 500 M3s.8
Tracks could often last 1,000 miles, whereas other models required replacement at 500 miles.
During production the riveted turret was replaced by a welded one 7-sided one.6,12 Also in early 1942 an all welded hull was produced.
It had volute spring suspension with the rear idler on the ground. This reduced the ground pressure and gave support to the rear of the tank.
The engines were in the rear with the drive going to the front sprockets, which was controlled by differential steering.7 The rear idler was located on the ground which helped in supporting the rear of the M3.6
The driver was on the left and the hull gunner/assistant driver on the right.6,7 They could see out through windshields in their hatches.6
The gunner and commander/loader were in seats that were in the M3's turret basket.6
Internally the M3 carried 56 gallons of fuel.6 Some tanks had two 25 gallon external tanks added, and these were jettisonable once combat started.6
M3: 5,8115,7,10, ~6,00011
Production: 1941 - ?11, 1941 - August 19425, March 1941 - August 19427
M3: Production started in March 1941 right after the last M2 was produced.1 In July 1943, the Ordnance Committee declared it obsolete. From mid-1941 a gyrostabilizer was installed with the gun. Had cupola on the left side of the turret. There was a sponson on each side of the vehicle which had a .30 caliber machine gun installed.12 The radios were in the left sponson and were usually the SCR508.
M3 Command Tank: Removal of turret and putting welded box superstructure with .50 cal MG on mount.10
M3 with Maxson Turret: In 1942 a quad Maxson .50 cal machine gun turret was put on in place of the turret. Rejected as similar equipment was on half-tracks.
M3 and T2 Light Mine Exploder: In 1942 a T2 mine exploder on a boom was developed and rejected as too unwieldy.
M3 or M3A1 with Satan Flame-gun: Produced in Hawaii for use by USMC. Gun was removed and flame thrower was installed.8 Capacity was 170 gallons and range of 40-60 yards. 20 converted in 1943. Used at Saipan, Tinian, and Guam.8
M3A1 with E5R2-M3 Flame-gun: Flame thrower put in place of hull machine gun.8 10 gallon capacity. Used at Saipan, Tinian, and Guam.8
T18 75 mm Howitzer Motor Carriage: Design started in September 1941. It was to provide a close support vehicle for the M3. Two test vehicles with mild steel superstructures were sent to the Aberdeen Proving Ground. This project was abandoned in April 1942 as it was unsatisfactory with it's high profile and being nose heavy.
T56 3" Gun Motor Carriage: Project started in September 1942 to mount a 3" in a modified M3A3 chassis. The gun was placed in the rear, and the engine was moved to the center. Had limited crew protection and was very heavy. Project dropped in February 1943.
T57 3" Gun Motor Carriage: Same as the T56, but with an up-rated Continental engine from the M3 medium. Project dropped in February 1943.
Russia1, China1, New Zealand1, and France received some as well.