When the M4 tank went into combat in North Africa with the British Army at the Second Battle of El Alamein in late 1942, it increased the advantage of Allied armor over Axis armor and was superior to the lighter German and Italian tank designs. For this reason, the US Army believed that the M4 would be adequate to win the war, and relatively little pressure was initially exerted for further tank development. Logistical and transport restrictions, such as limitations imposed by roads, ports, and bridges, also complicated the introduction of a more capable but heavier tank.[c] Tank destroyer battalions using vehicles built on the M4 hull and chassis, but with open-topped turrets and more potent high-velocity guns, also entered widespread use in the Allied armies. Even by 1944, most M4 Shermans kept their dual-purpose 75 mm gun. By then, the M4 was inferior in firepower and armor to increasing numbers of German upgraded medium tanks and heavy tanks but was able to fight on with the help of considerable numerical superiority, greater mechanical reliability, better logistical support, and support from growing numbers of fighter-bombers and artillery pieces. Later in the war a more effective armor-piercing gun, the 76 mm gun M1, was incorporated into production vehicles. For anti-tank work, British refitted Shermans with a 76.2 mm Ordnance QF 17-pounder gun (as the Sherman Firefly). Some were fitted with a 105 mm gun to act as infantry support vehicles.
The United States Army Ordnance Department designed the M4 medium tank as a replacement for the M3 medium tank. The M3 was an up-gunned development of the M2 Medium Tank of 1939, in turn, derived from the M2 light tank of 1935. The M3 was developed as a stopgap measure until a new turret mounting a 75 mm gun could be devised. While it was a big improvement when used by the British in Africa against German forces, the placement of a 37 mm gun turret on top gave it a very high profile, and the unusual side-sponson mounted main gun, with limited traverse, could not be aimed across the other side of the tank. Though reluctant to adopt British weapons into their arsenal, the American designers were prepared to accept proven British ideas. These ideas, as embodied in a tank designed by the Canadian General Staff, also influenced the development of the American Sherman tank. Before long American military agencies and designers had accumulated sufficient experience to forge ahead on several points. In the field of tank armament, the American 75 mm and 76 mm dual-purpose tank guns won the acknowledgment of British tank experts. Detailed design characteristics for the M4 was submitted by the Ordnance Department on 31 August 1940, but the development of a prototype was delayed while the final production designs of the M3 were finished and the M3 entered full-scale production. On 18 April 1941, the U.S. Armored Force Board chose the simplest of five designs. Known as the T6, the design was a modified M3 hull and chassis, carrying a newly designed turret mounting the M3's 75 mm gun. This would later become the Sherman.
The T6 prototype was completed on 2 September 1941. The upper hull of the T6 was a single large casting. It featured a single overhead hatch for the driver and a hatch in the side of the hull. In the later M4A1 production model, this large casting was maintained, although the side hatch was eliminated and a second overhead hatch was added for the assistant driver. The modified T6 was standardized as the M4, and production began in February 1942. The cast-hull models would later be re-standardized as M4A1, with the first welded-hull models receiving the designation M4. In August 1942, a variant of the M4 was put forth by the Detroit Arsenal to have angled, rather than rounded hull and turret armor. The changes were intended to improve the tank's protection without increasing weight or degrading other technical characteristics.
In World War II, the U.S. Army ultimately fielded 16 armored divisions, along with 70 separate tank battalions, while the U.S. Marine Corps fielded six tank battalions. A third of all Army tank battalions, and all six Marine tank battalions, were deployed to the Pacific Theater of Operations (PTO). Before September 1942, President Franklin D. Roosevelt had announced a production program calling for 120,000 tanks for the Allied war effort. Although the American industrial complex was not affected by enemy aerial bombing or submarine warfare as was Japan, Germany and, to a lesser degree, Great Britain, an enormous amount of steel for tank production was diverted to the construction of warships and other naval vessels. Steel used in naval construction amounted to the equivalent of approximately 67,000 tanks; and consequently, only about 53,500 tanks were produced during 1942 and 1943.
Early Shermans mounted a 75 mm medium-velocity general-purpose gun. Although Ordnance began work on the T20/22/23 series as Sherman replacements, the Army Ground Forces were satisfied with the M4 and Armored Force Board considered some features of the experimental tanks unsatisfactory. Continuing with M4 minimized production disruption but elements of the experimental designs were incorporated into the Sherman. Later M4A1, M4A2, and M4A3 models received the larger turret with high-velocity 76 mm gun trialled on the T23 tank. The first standard-production 76 mm gun-armed Sherman was an M4A1, accepted in January 1944, which first saw combat in July 1944 during Operation Cobra. Variants of the M4 and M4A3 were factory-produced with a 105 mm howitzer and a distinctive rounded gun mantlet, which surrounded the main gun, on the turret. The first Sherman variant to be armed with the 105 mm howitzer was the M4, first accepted in February 1944.
From May to July 1944, the Army accepted a limited run of 254 M4A3E2 "Jumbo" Shermans, which had very thick hull armor and the 75 mm gun in a new, better-protected T23-style turret ("Jumbos" could mount the 76 mm M1 cannon), to assault fortifications, leading convoys, and spearhead armored columns. The M4A3 model was the first to be factory-produced with the horizontal volute spring suspension (HVSS) system with wider tracks to distribute weight, beginning in August 1944. With the smooth ride of the HVSS, it gained the nickname "Easy Eight" from its experimental "E8" designation. The M4 and M4A3 105 mm-armed tanks, as well as the M4A1 and M4A2 76 mm-armed tanks, were also eventually equipped with HVSS. Both the Americans and the British developed a wide array of special attachments for the Sherman, although few saw combat, remaining experimental. Those that saw action included a bulldozer blade, the Duplex Drive system, flamethrowers for Zippo flame tanks, and various rocket launchers such as the T34 Calliope. British variants (DDs and mine flails) formed part of the group of specialized vehicles collectively known as "Hobart's Funnies" (after Percy Hobart, commander of the 79th Armoured Division).
During the later years of the war, general purpose high explosive ammunition was preferred for fighting Japanese tanks because armor-piercing rounds, which had been designed for penetrating thicker steel, often went through the thin armor of the Type 95 Ha-Go (the most commonly encountered Japanese tank) and out the other side without stopping. Although the high-velocity guns of tank destroyers were useful for penetrating fortifications, M4s armed with flamethrowers were often deployed, as direct fire seldom destroyed Japanese fortifications.
The Israeli Defense Force used Shermans from its creation in 1948 until the 1980s, having first acquired a single M4A2 lacking the main armament from British forces as they withdrew from Israel. The popularity of the tank (having now been re-armed) compared to the outdated, 1934-origin French Renault R35 interwar light tanks with their 37 mm short-barreled guns, which made up the bulk of the IDF's tank force, led to the purchase of 30 unarmed M4(105 mm)s from Italian scrapyards. Three of these, plus the original M4A2, saw extensive service in the 1948-9 war of independence. The remainder were then serviced and rearmed with 75 mm guns and components whenever these became available, composing a large part of Israeli tank forces for the next eight years. The 75 mm-armed Shermans were replaced by M4A1 (76 mm) Shermans imported from France before the 1956 Suez Crisis after it was realized that their armor penetration was insufficient for combat against newer tanks such as the IDF Centurions as well as the T-34-85s being delivered to Egyptian forces. During further upgrades, the French military helped develop a conversion kit to upgrade about 300 Shermans to the long high-velocity 75 mm gun CN 75-50 used in the AMX-13. These were designated Sherman M-50 by the Israelis. Before the Six-Day War in 1967, the Israeli Army upgraded about 180 M4A1(76)W HVSS Shermans with the French 105 mm Modèle F1 gun, re-engined them with Cummins diesel engines, and designated the upgraded tank Sherman M-51. The Sherman tanks, fighting alongside the 105 mm Centurion Shot Kal and M48 Patton tanks, were able to defeat the T-34-85, T-54/55/62 series, and IS-3 tanks used by the Egyptian and Syrian forces in the 1967 Six-Day War.
As the Sherman was being designed, provisions were made so that multiple types of main armament (specified as a 75 mm gun, a 3-inch gun, or a 105 mm howitzer) could be mounted in the turret. The possibility of mounting the main gun of the M6 heavy tank, the 3-inch gun M7, in the turret of the M4 Sherman was explored first, but its size and weight (the weapon was modified from a land-based antiaircraft gun) made it too large to fit in the turret of the Sherman. Development on a new 76 mm gun better-suited to the Sherman began in fall 1942.
In early 1942, tests began on the feasibility of mounting a 105 mm howitzer into the turret of the Sherman. The basic 105 mm howitzer M2A1 was found to be ill-designed for mounting in a tank turret, so it was completely redesigned and re-designated the 105 mm howitzer M4. After modifications to the turret (concerning the balancing of the gun and the strength of the power traverse) and interior of the hull (concerning the stowage of the 105 mm ammunition), the Ordnance Department expressed its approval of the project, and production of M4 tanks armed with 105 mm howitzers began in February 1944. 2b1af7f3a8