The M-3 Grant/Lee evolution needed to happen quickly. The invasion of Poland, the British experience in the desert, and the invasion of France all showed that a 37mm gun was not powerful enough to deal with enemy tanks.
While German Panzerkampfwagen IIIs and Panzerkampfwagen IVs were still racing across the French countryside in early June 1940, demands were made on the U.S. Ordnance Department for a heavier tank gun.
In August 1940 General Adna R. Chaffee, the commander of the new Armored Force, met with representatives from the Ordnance Department to finalize plans to produce the M-2A1 Medium Tank. During the meeting, he demanded and received agreement to build a tank capable of carrying a 75mm gun.
The M-2 Medium Tank chassis and hull could not support a larger turret or absorb the recoil forces from a 75mm gun. To speed the new tank into production, a design compromise was reached. The new tank would mount a 75mm gun in a limited traversing sponson on the right side of a heavier chassis and hull from a previous experimental tank.
Thus, even while the Detroit Arsenal -- the factory intended to build the M-2 Medium Tank -- was itself being built, the M-2 was canceled, and a new contract for the M-3 -- for which design work had not yet been completed -- was issued.
The M-3 thus evolved from the M-2, but indirectly. Central to the M-3's production was a new tank factory -- the Detroit Arsenal.
In 1939, when it was clear that the United States would have to rearm, Ordnance sought to place contracts for tank production with existing heavy industrial companies. But William Knudson, president of General Motors Corporation and a member of the National Defense Advisory Commission (NDAC), pointed out that heavy industrial firms, such as the builders of railroad cars and generators, were inexperienced in mass production, particularly the overwhelming quantities that would soon be needed.
Knudson's arguments persuaded the NDAC, and they in turn persuaded the Army. The Detroit Arsenal was commissioned specifically to build tanks. The facility was built in six months on 113 acres of land in Warren, Michigan. It was the largest manufacturing facility built to that time, and it was operated by Chrysler Motors.
In its most widely produced form, the M-3 used a cast-and-welded hull that was versatile enough that a diesel rather than an aircraft engine could be fitted when the latter was in short supply.
One version -- the M-3A4 -- even had four Chrysler automobile engines combined in one power pack and was referred to as the "eggbeater." The M-3's armor plate of 1.45 inches maximum was considered adequate when the design was finalized in 1940.
The M-3 was heavily armed: a .30 caliber Browning machine gun in a rotating cupola atop the turret, two more .30 caliber Browning machine guns mounted in the tank's bow, a 37mm auxiliary gun in the revolving turret plus a coaxial .30 caliber Browning machine gun, and a 75mm M2 or M3 main gun mounted in a sponson on the tank's right side. The main gun could fire either armor-piercing or high-explosive ammunition.
See the next page for a rundown of M-3 Grant/Lee nomenclature.
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