The M3 medium tank series appeared at a time when Allied armor (in respects to both armor protection and armament) was generally inferior to their German counterparts in Europe and North Africa. The M3 evolved from the M2 medium tank foray and served as essentially an interim solution until the arrival of the fabled M4 Shermans into the fray. As it stood, the M3 was an adequate solution not without its flaws but served the Allies well in returning control of North Africa back in their favor. Though often written off despite her contributions, the M3 played a pivotal role in the early-to-middle years of World War 2.
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.
At its core, the base M3 was powered by a Wright (later Continental) R975 EC2 series engine of up to 400 horsepower. This powerplant was mated to a synchromesh, 5-speed (featuring a single reverse speed) transmission and a Vertical Volute Spring Suspension (VVSS) system. Top speed was limited to 24.8 miles-per-hour on road and drastically reduced to 16.15 miles-per-hour off-road. Range peaked at just under 120 miles.
Primary armament consisted of a 1 x 75mm Gun M2/M3 with 46 projectiles onboard. The main gun of the M3 was key in that it could fire both armor piercing (AP) projectiles and high-explosive (HEAT) projectiles equally (earlier tank systems required the use of two separate guns/turrets for this cause). This was augmented by the 1 x 37mm M5/M6 fitting in the turret with 178 projectiles in tow. Anti-infantry defense was handled by up to 4 x .30-06 Browning M1919A4 machine guns with 9,200 rounds of ammunition.
The base M3 (Lee I / Grant I)) featured a riveted hull and a gasoline-fueled engine. These were followed into service by the M3A1 which sported a cast rounded upper hull. 300 of this type were produced. The M2A2 came online next featuring a welded, straight-edged hull, and only saw 12 or so produced. The M2A3 was a twin-engined GM-powered 6-71 diesel derivative mated to a welded hull. The side doors consistent to the earlier M3's were eliminated as a ballistics weak spot. 322 of this type were produced.
The M3A4 featured a longer hull made of riveted construction. This variant is of particular note due to its fitting of the Chrysler A-57 "Multibank" engine. The Multibank combined five complete engines in a star pattern formation and was a tank mechanic's worst nightmare. This layout also necessitated a longer hull. 109 of the M3A4 series were produced in whole.
The M3A5 sported twin GM 6-71 diesel engines (a departure from the previous gasoline-fueled powerplants). The tank featured a riveted hull and up to 591 examples were produced.
Beyond its various combat forms, the M3 appeared in capable battlefield implements as well. This included the M31 Tank Recovery Vehicle (Grant ARV I), the similar M31B1 and M31B2 and the M33 "Prime Mover", the latter an artillery tractor derivative. The chassis was also utilized in the development of the 105mm Howitzer Motor Carriage, M7, commonly known as the "Priest". Additionally, the M3 chassis made up the 155 Gun Motor Carriage M12.
Likewise, the British evolved the M3 into their own dedicated battlefield roles that included the Grant ARV, Grand Command, Grant Scorpion III (fitted with a mine-clearing flail), Grant Scorpion IV (similar to Scorpion III but with extra engine power) and the Grant CDL. The Canadian "Cruiser Tank Ram" utilized the M3 chassis and fitted a conventional full-traverse turret but would never see combat action.
First contact by any M3 occurred in North Africa come 1942, first by the British and then later joined by a contingent of American-piloted M3's. Results were mixed with the British maintaining a better initial performance record. By the time of American involvement, German armor, experience and tactics had all improved and delivered a baptism of fire for M3 crews. At the very least, the M3 was on par with the German-fielded units and offered up a level playing field for the Allies for the first time in the war. The M3 proved to be a reliable machine and her 75mm was good for the moment. Her armor was highly regarded for it matched up well against the German weapons of the time. Limitations were its inherent flaws such as its slow off-road performance, limited traverse main gun and its high profile - making for somewhat easy pickings by enemy tanks with full traverse turrets or mobile anti-tank teams.
In the Pacific, M3's appeared in limited numbers and, as such, their reach in the region was restricted. It did, however, prove handy against the lightly-armored Japanese tanks. Future tank engagements in the region played out equally well for the Americans thanks to the arrival of the M4 Sherman series.
The Soviets had poor experiences from their M3's delivered via Lend-Lease. The system fared in a generally unfavorable way against the more mobile German armored tanks. Where the Soviets were looking for a tank capable of outgunning other tanks, the M3 proved a sorrowful disappointment and forced the Russians to look elsewhere.
In all, some 6,258 M3's were produced for all parties involved. Operators were led by the United States, Britain (via Lend-Lease or direct purchase), Australia, Brazil, Canada, New Zealand and the Soviet Union (via Lend-Lease). Production for all M3's ran from August of 1941 through December of 1942. The arrival of the capable M4 Sherman - and the Soviet T-34, German Panther and 75mm-armed Panzer IV for that matter - decreased all M3 combat roles substantially, effectively ending the type's reign in the war.