When the Germans invaded France in May 1940 the consequent tank actions were closely observed by various US Army agencies. From their observations the Americans learned that the next generation of medium tanks had to have at least a 75-mm (2.95-in) gun as their main armament, but this presented them with problems as their next tank generation, already being produced in prototype form, was armed with only a 37-mm (1.46-in) gun of the type already seen to be obsolete.
The American answer was swift and drastic: they simply took their existing design and altered it to accommodate the required 75-mm (2.95-in) gun. The turret of the new design (the Medium Tank M2, destined never to see active service) could not take the larger gun so the weapon had to be situated in the hull. Consequently the revised tank design retained the 37-mm (1.46-in) gun turret, while the main armament was located in a sponson on the righthand side of the hull. The 75-mm (2.95in) gun was a revised version of the famous French '75' field piece as made in the USA, but new ammunition converted it into what was for the time a powerful tank weapon. Secondary armament comprised four 7.62-mm (0.3-in) machine-guns (one in the commander's cupola atop the 37-mm/1.46in turret, one co-axial with the 37-mm/1.46-in gun, and two in the hull).
The new design became the Medium Tank M3, and was rushed into mass production in a factory meant for the earlier M2. Almost as soon as production started for the US Army, a British mission arrived in the United States on a purchasing trip to obtain tanks to replace those lost in France, and the M3 was high on its shopping list. They requested a few changes to suit their requirements, the most obvious of which were a revised turret rear outline to accommodate radio equipment and the absence of the cupola and this model was produced specifically for the British army. Once delivered the British knew the M3 as the General Grant I (or simply Grant I), and the first of them went into action at Gazala in May 1942 when they provided the Afrika Korps with a nasty fright as their arrival was entirely unexpected, their combination of armament and armour (12 mm/0.47 in minimum and 50mm/ 1,97 in maximum) proving most useful.
The Grants were later joined in British service by the unmodified M3 which was then labelled the General Lee I. Further improvement led to the M3A1 (Lee II) with welded construction, the uparmoured M3A3 (Lee IV) with two General Motors 6-71 diesels delivering 375 hp (280 kW), the M3A4 (Lee V) with the Chrysler A-57 multibank engine delivering 370 hp (276 kW), and the M3A5 based on the M3A3 but with a riveted hull. By the time production ended in December 1942 the total had reached 6,258 and the M3 was used in virtually every theatre of war in one form or another, Many were passed to the Red Army on a Lend-Lease arrangement.
The M3 turned out to be a reliable and hard-wearing vehicle, but its hulllocated main gun was often a cause of tactical difficulties as its traverse was very limited. But it did provide the punch that Allied 'tankies' required at that time, Its tactical silhouette was really too high for comfort, but considering that the basic design was improvized and rushed into production, at a time when there were more questions being asked than answers provided, it turned out to be a remarkable effort. Many of the suspension and automotive features were later incorporated into other designs and continued to provide excellent service, but perhaps the main lesson to be learned from the M3 was the latent power of American industry that could churn out such a vehicle from scratch in such a short time.
As soon as the M4 entered service the M3s were usually withdrawn and converted to other roles such as armoured recovery vehicles, but in the Far East they remained in use until 1945 in both Grant and Lee forms. The M3 Grant was the 'British' version of the M3 Lee. Themain change was to the turret profile, which had a rear overhang to house a radio set, and the silhouette was lowered by omitting the machinegun cupola of the original turret.
Specification Medium Tank M3A2 Crew: 6 Weight: in action 27.24 tonnes Powerplant: one Continental R-975EC2 radial petrol engine developing 253,5kW(340hp) Dimensions: length 5.64 m (18 ft 6 in); width 2.72 m (8 ft 11 in); height 3.12 m (10 ft 3 in) Performance: maximum road speed 42 km/h (26 mph); maximum road range 193 km (120 miles); fording 1.02 m (3 ft 4 in); gradient 60 per cent; vertical obstacle 0.61 m (2 ft); trench 1.91 m (6 ft 3 in)