At the end June 1940 the National Munitions Program was introduced to address the United States lack of readiness in case of war across all branches of the armed forces.

[9] In mid July, Armored Force under Brigadier General Adna R. Chaffee Jr. was formed to take over responsibility for tanks which had previously been split between the Infantry and Cavalry commands.

An experimental modification of an improved M2 Medium into a self-propelled gun - the T5E2 - had been tested with a 75m pack howitzer in the front hull and it was decided to base the interim design on this work.

[13] The design was unusual because the main weapon – a larger caliber, medium-velocity 75 mm gun – was in an offset sponson mounted in the hull with limited traverse.

The sponson mount was necessary because, at the time, American tank plants did not have the design experience necessary to make a gun turret capable of holding a 75 mm weapon.

The M3 was tall and roomy: the power transmission ran through the crew compartment under the turret basket to the gearbox driving the front sprockets.

It was originally developed at the Rock Island Arsenal for T5 Phase III in 1938[15] but in 1940 Spicer Manufacturing Company was contracted to refine the design before serial production.

[citation needed] There were also two .30-06 (7.62 mm caliber) Browning M1919A4 machine guns mounted in the hull, fixed in traverse but adjustable in elevation, which were controlled by the driver.

British experts had viewed the mock-up in 1940 and identified features that they considered flaws – the high profile, the hull mounted main gun, the radio position in the hull rather than in the turret, the riveted armor plating (whose rivets tended to pop off inside the interior in a deadly ricochet when the tank was hit even by non-penetrating rounds), the smooth track design, insufficient armor and lack of splash-proofing of the joints.

After extensive losses in Africa and Greece, the British realized that to meet their needs for tanks, they would have to take both the Lee and the Grant types.

A further 1,386 were exported to the Soviet Union,[34] although only 957 of these reached Russian ports due to German U-boat and air attacks on Allied convoys.

The US 1st Armored Division had been issued the new M4 Sherman, but had given up one regiment's worth to the British Army so that it could use them in the Second Battle of El Alamein (October-November 1942).

The M3 was generally appreciated during the North African campaign for its mechanical reliability, good armor protection, and heavy firepower.

[citation needed] However, the high silhouette and low, hull-mounted 75 mm were tactical drawbacks since they prevented fighting from a hull-down firing position.

Beginning from 1941, 1,386 M3 medium tanks were shipped from the US to the Soviet Union, with 417 lost when their transporting vessels were sunk by German submarine, naval and aerial attacks en route.

[43] Due to the vehicle's petrol-fueled engine, a high tendency to catch fire, and its vulnerability against most types of German armor the Soviet troops encountered from 1942 onwards, the tank was almost entirely unpopular with the Red Army since its introduction in the Eastern Front.

[44] In the letter sent to Franklin Roosevelt (18 July 1942), Stalin wrote: "I consider it my duty to warn you that, according to our experts at the front, U.S. tanks catch fire very easily when hit from behind or from the side by anti-tank rifle bullets.

In the Pacific War, armor played a relatively minor role for the Allies as well as for the Japanese, compared with that of naval,[46] air,[47] and infantry units.

Following the better-known landing at Tarawa, the US 27th Infantry Division made an amphibious assault on Makin Island with armored support from a platoon of M3A5 Lees equipped with deep-wading kits belonging to the US Army's 193rd Tank Battalion.

After British Commonwealth forces in Europe and the Mediterranean began receiving M4 Shermans, about 900 British-ordered M3 Lees/Grants were shipped to the Indian Army.

[33] They were used by the British Fourteenth Army[51] until the fall of Rangoon,[51] regarded as performing "admirably" in their original intended role of supporting infantry in Burma between 1944 and 1945.

At the beginning of the war, Australian Army doctrine viewed tank units as minor offensive components within infantry divisions.

It had no dedicated armored branch and most of its very limited capabilities in tank warfare had been deployed to the North African Campaign (i.e. three divisional cavalry battalions).

The Australian Armoured Corps initially included the cadres of three armored divisions – all of which were equipped at least partly with M3 Grants made available from surplus British orders.

During April–May 1942, the 1st Armoured Division's regiments were reported to be re-equipping with M3 Grants and were training, in a series of large exercises, in the area around Narrabri.

[55] In January 1943, the main body of the 1st Armoured Division was deployed to home defense duties between Perth and Geraldton, where it formed part of III Corps.

[54] By the middle of the war, the Australian Army had deemed the Grant to be unsuitable for combat duties overseas, and M3 units were re-equipped with the Matilda II before being deployed to the New Guinea and Borneo Campaigns.

[55] During the war, the Australian Army had converted some M3 Grants for special purposes, including a small number of bulldozer variants, beach armoured recovery vehicles, and wader prototypes.

Many M3s deemed surplus to Australian Army requirements were acquired by civilian buyers during the 1950s and 1960s for conversion to earthmoving equipment and tractors.

By mid-1942, with the introduction of the German Tiger I, the up-gunning of the Panzer IV to a long 75 mm gun, and the first appearance in 1943 of the Panther, along with the availability of large numbers of the M4 Sherman, the M3 was withdrawn from service in the European theater.