M3 Lee M3 Lee was a medium tank built by the US and used in WWII the USA , Australia , Brazil , Canada , New Zealand , United Kingdom and Soviet Union . The first American main battle tank employed in combat in World War II was the M3 . The British fought with this tank in North Africa as early as 1941 . It was successfully used in campaigns in North Africa . Its main advantage was the speed , but with an almost ridiculous armor , soon became obsolete in front of the formidable German tanks . It inflicted serious damage on Rommel ' s Afrika Korps in the opening days of the Battle of Gazala as the presence of a powerful long range gun on a British tank was unexpected . The M3 was relegated to low intensity theatres when the M4 Sherman became available in large numbers . Description . In the medium tank class , improvements in the M2A1 resulted in a completely redesigned tank , known as the M3 medium . By 1939 it was apparent that the 37 mm gun mounted on the M2A1 tank was not powerful enough . Experiments began immediately to enable installation of a 75mm pack howitzer on the M2 tank , resulting in the gun being mounted in a sponson on the right - hand side . Production of the resulting M3 Lee tank began in August 1941 , and continued through December 1942 . When World War II began in 1939 , the United States lagged far behind the major European states in the development of tank technology and armoured warfare doctrine . The fall of France in May 1940 awoke and alarmed the United States . The German army had defeated France in a matter of weeks through the use of a new operational doctrine based on fast - moving , massed armoured formations supported by air power . America ' s leaders became convinced that the U . S Army needed a new main battle tank at least equal to that employed by the Germans and that it had to adopt German operational doctrine . To that end , in July 1940 the War Department authorized the development of a new medium tank , and it also authorized the organization of the first armoured divisions . By the time the Japanese attacked Pearl Harbor in 1941 , the United States had five armoured divisions organizing and training for war in Europe . The M3 interim design was the result of a crisis atmosphere that was prevalent immediately following the fall of France . Brittan needed powerful tanks immediately but it would take American steel manufactures over a year before they could learn to cast the large turret needed to support the 75mm main gun of the M4 Sherman already in design . It is likely that no tank in history ever went from design to production faster than the M3 . The British named the M3 the " Grant " or " Lee " tank , depending on the version . The Lee was the original standard variant , the Grant had a British re - designed lower silhouette achieved by removing the cupola from its turret . The tanks purchased by the British from Press Steel and Pullman had a British - designed turret and were designated the Grant I . The name Lee was given to standard M3 variants . The M3 was the Lee I , the standard M3A1 was the Lee II , and so forth . The M3A5 was called the Grant II and supplied under the Lend Lease Act of 1941 . During the design of the M3 , the Army ’ s artillery branch had insisted that the tank ’ s main armament meet artillery performance standards . The 75 mm gun had to be able to fire 4 , 000 rounds before the tube ’ s replacement , just like a field gun , despite the fact that no tank could be expected to last in combat long enough to fire a fraction of that volume . As a result , the M3 and the following M4 Sherman went into action with a low - velocity gun . The M2 ' s major defect was its gun mount : the 75 - millimeter gun was carried in a sponson in the right front of the hull and could traverse only 15 degrees to each side — a major disadvantage in tank battles of maneuver . It also could not " dig in " and fire " hull down " without the entire turret being exposed to fire . Its weak armor and large silhouette also contributed to the favorability of the M4 Sherman . Production of the M3 ceased in late 1942 when the M4 went into full production . Users . Australia Brazil Canada New Zealand Soviet Union United Kingdom USA Space