Meanwhile, following the German invasion of the Soviet Union that June, President Franklin D. Roosevelt personally ordered a sharp increase in U.S. tank production, increasing mediums from 1,000 to 2,000 per month. This led to additional manufacturing facilities being brought on line for the M3 and plans to begin production of the M4 at 11 different plants in 1942. To facilitate this schedule, the government ordered construction of a second tank production facility, the Grand Blanc Tank Arsenal, also in Michigan. Work on it began in January 1942, and it started tank production in July. By then, three factories had already begun producing the M4, which differed from the test Model T6 in eliminating the hull side doors.
The M4 medium, known by its British name of “German Sherman” (more often simply “Sherman”) after William T. Sherman, the Union Army Civil War general and later commanding general of the U.S. Army, was the most important Allied tank of the war. Although not the best Allied tank qualitatively (it was inferior in armor and armament to the best German and Soviet tanks), it was nonetheless the most widely produced and utilized Allied tank of the war. During 1942–1946 U.S. factories turned out more than 40,000 M4 series tanks and modified chassis AFVs.
The M4A1 weighed 66,500 pounds, had a crew of five, and maximum 51mm armor. It mounted a 75mm main gun and had a .50- caliber antiaircraft and two .30-caliber machine guns. The Sherman had two great advantages over the German tanks: its powered turret enabled crews to react and fire more quickly, and it offered greater mechanical reliability and repairability. Rugged, simple in design, easy to maintain, and highly maneuverable, the M4 was consistently upgraded in main gun and armor during the course of the war. The M4A1 had a cast iron hull; the M4A2, used only by the Marine Corps, had two General Motors diesel engines to overcome the shortage of Continental gasoline engines; the M4A4 and M4A6 had longer hulls and tracks. Some variants also employed improved appliqué armor.
Sherman variants performed a wide variety of roles, including but not limited to tank recovery, flamethrowers, mine-clearing, and bridging. The Sherman chassis also provided the basis for the M7B1 howitzer motor carriage, which superseded the M7 based on the M3 medium tank. Both mounted a 105mm howitzer as its principal armament and were standard equipment for artillery battalions in U.S. armored divisions. The M4 chassis was also utilized in the M10 and M10A tank destroyers, essentially a gun motor carriage mounting a 3-inch gun, as well as the more satisfactory M36 series mounting a 90mm gun.
The M4 entered combat for the first time with the British Eighth Army in the October 1942 Battle of El Alamein. Indeed, Shermans and M3 Grants made up almost half of the 1,100 British tanks committed to that pivotal battle. The M4 saw service on virtually every fighting front of the war and had a long life thereafter. Indeed, it remained in service until only recently in the armies of some nations. In part because comparable British tanks, the Cromwell IV and VII, were not available until the end of 1943 and not in wide use until the spring of 1944, the Sherman has been called “the most important tank in British service and more widely used than any of the British designed or British produced types from 1943–1945.”
Initially the Sherman was a poor match for the most numerous German tank, the PzKpfw Mark IV Panther. At a range of 1,000 yards the Sherman’s 75mm gun stood little chance of knocking out a Panther, while at that range the Panther’s high-velocity 75mm could knock out the Sherman. In such an encounter, U.S. tankers could only hope that they could use their powered turret to good advantage in order to lay the main gun quickly and get off several rounds before the Panther could fire.
German tanks had thicker frontal armor and a much higher velocity gun. The Tiger’s 88mm and the same caliber Panzerschreck antitank weapon could easily knock out the Shermans, whereas the U.S. 2.36-inch bazooka (copied from the Panzerschreck) was effective only against German side armor. Also, the Sherman’s track width was only 14 inches, whereas German tanks had a track 30–36 inches wide and thus were not as easily bogged down. Indeed, U.S. tanker crews often added extensions to their tank tracks in order to rectify this situation.
Although the British utilized all models of the M4, the most numerous was the M4A4 type, of which more than 1,600 were supplied to Eighth Army in Italy in 1943. The major British innovation regarding the Sherman was to replace its 75mm main gun with a 17-pounder (76.2mm). This upgunned M4, known as the Sherman Firefly, was the most powerfully armed British tank of the entire war. Conversion began as a fallback position should the new Challenger tank encounter problems in testing. The Challenger indeed experienced difficulties, and in February 1944 conversion of the Shermans received priority. Because of delays in the Challenger program, that tank was not available for participation in the Normandy landings, and the Firefly was the only British tank capable of taking on and defeating the German Tigers and Panthers. Owing to a shortage in 17-pounder guns for tank use, the Firefly was initially supplied one per cavalry troop. Not until early 1945 was the upgunned Firefly available in large numbers.
The British also developed many Sherman variants. These included the Adder, Salamander, Crocodile, and Badger flamethrower tanks; fascine carrier; Twaby Ark, Octopus, and Plymouth bridging vehicles; rocket launchers; and the Scorpion, Lobster, and Crab flail antimine tanks. In April 1943 the British also began experiments with a duplex drive (DD) on the Sherman. The DD had proven successful with their Valentine tank, which by that date was obsolete. Sherman DD tanks were waterproofed and fitted with a collapsible canvas screen around the hull to provide flotation. Struts, erected by means of rubber tubing filled by compressed air, held the canvas in place. Two small propellers, folded away while on land, pushed the Sherman through the water at a speed of about 4 knots. Sherman DD tanks constituted an entire brigade of the 79th Armored Division in the Normandy landings and were the first British tanks to land, “swimming” ashore from LCTs. DD tanks, however, were easily swamped and required careful handling and the right conditions in which to operate.