By the time of the German invasion of Poland, the United States had little in the way of an effective armor corps thanks primarily to a lack of vision and a lack of funding from the US Congress. Much dedication during the inter-war years following World War 1 placed a greater emphasis on light tank designs, seeing that these systems would benefit the standard infantryman more than medium tanks. The M2 light tank was such a development, but come 1936, the US Army sought a newer and more powerful medium-class tank based on the successful suspension system of the light-class M2's.
The T5 was developed as a five-man system with a primary armament of a 37mm main gun in a fully-traversable turret. One derivative of the T5 became the T5E2 and sported a 75mm main gun, though this was fitted to a World War 1-style side sponson that offered limited traverse. The T5E2 did feature a turret, however this had accommodations for one crew member and the armament was nothing more than an anti-infantry .30 caliber machine gun.
The T5 itself was an impressive design considering the times. It featured a broad and sharply-angled glacis plate with a hull sporting straight-faced sides. The turret fitted the 37mm main gun with 360-degree rotation as well as 2 x .30 caliber machine guns. There were four machine gun sponsons with limited traverse fitted to the four corners of the superstructure - two facing forward and two facing aft. The glacis plate sported an additional pair of .30 caliber machine guns emerging from the upper hull. The profile was admittedly high, nearly one and one-half times the height of an average man. The vehicle's sides were characterized by the three sets of road wheels with two wheel bogies to a set. Vision slots were afforded the driver, superstructure occupants and the turret operator. The T5 graduated to a production designation of M2 Medium Tank.
As the conflict in Europe continually unfolded, the idea of a medium tank in the United States evolved. The M2 was revised into the improved M2A1 Medium Tank. Despite its impressive appearance, the M2 was still little more than a mobile machine gun platform with a main gun capable of engaging light armored vehicles at best. It would have made for an excellent design in World War 1 but the speed at which the German invasions of Poland, and now France, had made the M2A1 immediately obsolete. With the fall of Paris, the US Congress prepared for war and authorized funding for the modernization of the American military. 94 M2A1 tanks were produced solely for training purposes.
By August of 1940, a new medium tank design was called for, this sporting improved performance, better armor allocation as it pertained to the most potent German anti-tank gun at the time and a more potent main gun armament. The design, based on the T5E2 mentioned earlier, was ready by the beginning of 1941 as the aptly-designated "M3".
The design of the M3 was peculiar to say the least, sort of a tank caught between two eras of warfare. Though the new design fitted a more potent 75mm main gun, this was placed in a limited traverse turret offset to the right of the superstructure. This was essentially a requirement for the time for now proven turret system was available for immediate service in the United States. Rather than spend critical time and funds in developing a useful turret, it was seen that the M3 should hit the production lines in the shortest amount of time possible. Likewise, the powerplant - an aircraft-based Wright air-cooled engine - proved lacking but there was little time to waste in fielding the M3. A full-traverse turret was in fact utilized on the M3, though this fielded the less-than-adequate primary armament of a 37mm main gun. Atop this turret was still another smaller turret housing a .30 caliber machine gun.
The M3 was a tall design, peaking at over 10 feet in height. As anyone who knows armored warfare, they would know the dangers of fielding a tall tank. The turret-on-turret layout did not help matters in keeping the M3's profile at an acceptable height. To make matters worse, the superstructure itself was of a relatively tall design. This was necessitated by how high the engine sat in its rear hull mounting. This height forced the propeller shaft, running from rear to front toward the gearbox, to achieve a downward position. This angled shaft forced the crew cabin to be placed higher in the design than one would have liked in a tank. This further forced the main turret to be raised and the additional cupola system did not help matters much. The original M3 order called for a crew of seven personnel. This was later whittled down to six and ultimately five crewmembers when the radio operator's position was consolidated.
As it was, the US Army - and the free world for that matter - needed a tank that was somewhat capable, ready for full-scale production and available in quantity. The M3 proved to be the order of the day. The US Army committed to the M3 with a first-run production of 4,924 units beginning in the middle of 1941 despite some reservations by Army personnel as to the effectiveness of the vehicle in regards to performance. The M3 was no speedster and the engines allotted to the design was vastly under-powered for what was to be expected of this medium tank. Nonetheless, the M3 was a much-needed medium tank addition and the dwindling supply of British tanks in North Africa sped up production. A second batch of 1,334 vehicles soon followed and made up a variety of marks based on configuration. These became the M3A1 (Lee II), M3A2 (Lee 3), M3A3 (Lee IV/Lee V), M3A4 (Lee VI) and the M3A5 (Grant II) series marks. When in service with the British Army, the M3 took on the names of "General Lee" and "General Grant" (or simply "Lee" and "Grant"). The British Army had a tradition of naming US-produced tanks in their service on American Civil War generals, with the two in question being Robert E. Lee and Ulysses S. Grant. This was also apparent in the M3/M5 "Stuart" light tank series as well as the soon-to-arrive M4 "Sherman" series. British M3's were also refitted to utilized a lower-profile "British Friendly" turret that incorporated a rear-mounted bustle for radio equipment, in effect deleting one of the crewmember positions.
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