M4 Sherman

A Sherman DD amphibious tank of 13th/18th Royal Hussars in action against German troops using crashed Horsa gliders as cover near Ranville, Normandy, 10 June 1944

As the United States approached entry into World War II, armored employment was doctrinally governed by Field Manual 100–5, Operations (published May 1941, the month following selection of the M4 tank's final design). That field manual stated:

The armored division is organized primarily to perform missions that require great mobility and firepower. It is given decisive missions. It is capable of engaging in all forms of combat, but its primary role is in offensive operations against hostile rear areas.[18]

The M4 was, therefore, not originally intended primarily as an infantry support tank. It placed tanks in the "striking echelon" of the armored division, and placed the infantry in the "support echelon", without directing that tanks should only seek to attack other tanks, thus leaving target selection up to the field commander based on what types of units were available to him to attack. A field manual covering the use of the Sherman (FM 17–33, "The Tank Battalion, Light and Medium" of September 1942) described fighting enemy tanks when necessary as one of the many roles of the Sherman, but devoted only one page of text and four diagrams to tank-versus-tank action, out of 142 pages.[19] This early armored doctrine was heavily influenced by the sweeping early war successes of German blitzkrieg tactics. By the time M4s reached combat in significant numbers, battlefield demands for infantry support and tank versus tank action far outnumbered the occasional opportunities of rear-echelon exploitation.

United States doctrine held that the most critical anti-tank work – stopping massed enemy tank attacks – was primarily to be done by towed and self-propelled anti-tank guns, operated by "Tank Destroyer" battalions, with friendly tanks being used in support if possible.[20] Speed was essential in order to bring the tank destroyers from the rear to destroy incoming tanks. This doctrine was rarely followed in combat, as it was found to be impractical. Commanders were reluctant to leave tank destroyers in reserve; if they were, it was also easier for an opposing armored force to achieve a breakthrough against an American tank battalion, which would not have all of its anti-tank weapons at the front during the beginning of any attack.[21]

During World War II, approximately 19,247 Shermans were issued to the U.S. Army and about 1,114 to the U.S. Marine Corps.[34] The U.S. also supplied 17,184 to Great Britain (some of which in turn went to the Canadians and the Free Poles), while the Soviet Union received 4,102[35] and an estimated 812 were transferred to China.[36] These numbers were distributed further to the respective countries' allied nations.

The U.S. Marine Corps used the diesel M4A2 and gasoline-powered M4A3 in the Pacific. However, the Chief of the Army's Armored Force, Lt. Gen. Jacob L. Devers, ordered that no diesel-engined Shermans be used by the Army outside the Zone of Interior (the continental U.S.). The Army used all types for either training or testing within the United States, but intended the M4A2 and M4A4 (with the A57 Multibank engine) to be the primary Lend-Lease exports.

Shermans were being issued in small numbers for familiarization to U.S. armored divisions when there was a turn of events in the Western Desert campaign. Axis forces had taken Tobruk and were advancing into Egypt and Britain's supply line through the Suez Canal was threatened. The US considered collecting all Shermans together so as to be able to send the 2nd Armored Division under Patton to reinforce Egypt, but delivering the Shermans directly to the British was quicker and over 300 – mostly M4A1s, but also including M4A2s – had arrived there by September 1942.[22][37]

The Shermans were modified for desert warfare with sandshields over the tracks and other stowage. The Sherman first saw combat at the Second Battle of El Alamein in October 1942 with the British 8th Army. At the start of the offensive, there were 252 tanks fit for action. These equipped the British 9th Armoured Brigade (with the New Zealand Division), 2nd Armoured Brigade (1st Armoured Division) and 8th and 20th Armoured Brigades (10th Armoured Division). Their first encounter with tanks was against German Panzer III and IV tanks with long 50 mm and 75 mm guns engaging them at 2,000 yards (1,800 m). There were losses to both sides.[38]

The first U.S. Shermans in battle were M4s and M4A1s in Operation Torch the following month. On 6 December, near Tebourba, Tunisia, a platoon from the 2nd Battalion, 13th Armored Regiment was lost to enemy tanks and anti-tank guns.[39]

Additional M4s and M4A1s replaced M3s in U.S. tank battalions over the course of the North African campaign.

The M4 and M4A1 were the main types in U.S. units until the fall of 1944, when the Army began replacing them with the preferred M4A3 with its more powerful 500 hp (370 kW) engine. Some M4s and M4A1s continued in U.S. service for the rest of the war. The first Sherman to enter combat with the 76 mm gun in July 1944 was the M4A1, then the M4A2 ,closely followed by the M4A3. By the end of the war, roughly half the U.S. Army Shermans in Europe had the 76 mm gun. The first HVSS-equipped Sherman to see combat was the M4A3(76)W in December 1944.

Under Lend-Lease, 4,102 M4A2 medium tanks were sent to the Soviet Union. Of these, 2,007 were equipped with the original 75 mm main gun, with 2,095 mounting the more-capable 76 mm gun. The total number of Sherman tanks sent to the USSR under Lend-Lease represented 18.6% of all Lend-Lease Shermans.[40] The first 76 mm-armed M4A2 Shermans started to arrive in Soviet Union in the late summer of 1944.[41]

The Red Army considered the M4A2 to be much less prone to catch fire due to ammunition detonation than the T-34/76, but the M4A2 had a higher tendency to overturn in road accidents and collisions or because of rough terrain than the T-34 due to its higher center of gravity.[42]

By 1945, some Red Army armoured units were equipped entirely with the Sherman. Such units included the 1st Guards Mechanized Corps, the 3rd Guards Mechanized Corps and the 9th Guards Mechanized Corps, amongst others. The Sherman was largely held in good regard and viewed positively by many Soviet tank crews, with compliments given to its reliability, ease of maintenance, generally good firepower (referring especially to the 76 mm gun version) and decent armour protection,[43] as well as an auxiliary power unit (APU) to keep the tank's batteries charged without having to run the main engine, as was required on the T-34.[44]

Chinese M4A4 Sherman in the CBI Battlefield

While combat in the European Theater of Operations (ETO) often consisted of high-profile armored warfare, the mainly naval nature of the Pacific Theater of Operations (PTO) relegated it to secondary status for both the Allies and the Japanese. While the U.S. Army fielded 16 armored divisions and 70 separate tank battalions during the war, only a third of the battalions and none of the divisions were deployed to the Pacific Theater.[45] The Imperial Japanese Army (IJA) deployed only their 2nd Tank Division to the Pacific during the war.[46] Armor from both sides mostly operated in jungle terrain that was poorly suited to armored warfare. For this type of terrain, the Japanese and the Allies found light tanks easier to transport and employ.[47]

During the early stages of combat in the Pacific, specifically the Guadalcanal Campaign, the U.S. Marine Corps' M2A4 light tank fought against the equally-matched Type 95 Ha-Go light tank; both were armed with a 37 mm main gun. However, the M2 (produced in 1940) was newer by five years.[48] By 1943, the IJA still used the Type 95 and Type 97 Chi-Ha medium tanks, while Allied forces were quickly replacing their light tanks with 75 mm-armed M4s.[49] The Chinese in India received 100 M4 Shermans and used them to great effect in the subsequent 1944 and 1945 offensives in the CBI Battlefield.

As part of Operation Dexterity, an M4A1 (75 mm) advances through a tropical rain forest on New Britain, in the South-West Pacific

To counter the Sherman,[50] the Japanese developed the Type 3 Chi-Nu and the heavier Type 4 Chi-To; both tanks were armed with 75 mm guns, albeit of different type. Only 166 Type 3s and two Type 4s were built, and none saw combat; they were saved for the defense of the Japanese home islands, leaving 1930s vintage light and medium armor to do battle against 1940s built Allied light and medium armor.

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.[51][52]

Last type in US service: M4A3(76)W HVSS Sherman used as artillery in firing position during the Korean War

After World War II, the U.S. kept the M4A3E8 '"Easy Eight" in service, with either the 76 mm gun or a 105 mm M4 howitzer. The Sherman remained a common U.S. tank in the Korean War, where it fought alongside the M26 Pershing and M46 Patton. The M4A3(76)W HVSS Sherman and T-34-85 were comparable and could destroy each other at normal combat ranges, although the use of High Velocity Armor Piercing ammunition, advanced optics, and better crew training gave the Sherman an advantage.[53] The M4A3(76)W HVSS Sherman, using 76 mm HVAP ammunition, destroyed 41 enemy tanks from July–November 1950. The lighter M4A3(76)W HVSS tank became the preferred U.S. tank in the later phases of the war in Korea, due to the mechanical reliability of the M4, its ease of maintenance, and its driveability compared to the M26 tank.[54]

The U.S. Army replaced the M4 in 1957, in favor of the M48 Patton and M60 Patton The U.S. continued to transfer Shermans to its allies, which contributed to widespread foreign use.

The Israeli Defense Force used Shermans from its creation in 1948 until the 1980s, having first acquired a single M4A2 lacking main armament from British forces as they withdrew from Israel.[55] 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(105mm)s from Italian scrapyards.[55] 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 realised 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.[56] 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 Sh'ot 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.[57]

M4A3s were also used by British forces in Indonesia during the Indonesian National Revolution until 1946, when they were passed on to the KNIL, which used them until 1949 before they were passed on to the Indonesian Army.[58]

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.[59] 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.[60]

The Sherman would enter combat in 1942 equipped with the 75 mm gun M3, a 40-caliber gun that could penetrate 88 mm (3.5 in) of unsloped rolled homogeneous armor (RHA) at 100 meters (110 yd) and 73 mm (2.9 in) at 1,000 meters (1,100 yd) firing the usual M61 round.[61] Facing the early Panzer III and Panzer IV in North Africa, the Sherman's gun could penetrate the frontal armor of these tanks at normal combat ranges, within 1,000 yd (910 m). U.S. Army Intelligence discounted the arrival of the Tiger I in 1942 and the Panther tank in 1943, predicting that the Panther would be a heavy tank like the Tiger I, and doubted that many would be produced. There were also reports of British QF 6 pdr (57 mm) guns being able to destroy the Tiger I. However, this only happened at very close ranges and against the thinner side armor. Due to their misconceptions related to this, and also due to tests that seemed to prove that the 76 mm gun was able to destroy both the Tiger and the Panther, the leadership of Army Ground Forces were not especially concerned by the Tiger I. The criteria and results of the 76 mm gun tests were later ruled to have been inaccurate when compared to real-world conditions (tests against sections of American armor plate configured to resemble those found on a Panther tank suggested that the new M1A1 gun would be adequate, but testing against actual captured Panther tanks was never done), with Eisenhower even remarking that he was wrongly told by Ordnance that the 76 mm could knock out any German tank. The Army also failed to anticipate that the Germans would attempt to make the Panther the standard tank of their panzer divisions in 1944, supported by small numbers of Tiger I and IIs.[62]

When the newly-designed 76 mm gun, known as the T1, was first installed in the M4 in spring 1943, it was found to unbalance the turret, and the gun barrel also protruded too far forward, making it more difficult to transport and susceptible to hitting the ground when the tank traveled over undulating terrain. The barrel length was reduced by 15 in (380 mm) (from 57 calibers to 52), resulting in the M1 variant. Mounting this gun in the original M4 turret proved problematic, so the turret for the aborted T23 tank project was used instead for the definitive production version of the 76 mm M4 Shermans,[63] along with a modified version of the gun known as the M1A1.

Despite the Ordnance Department's development of new 76 mm and 90 mm anti-tank guns, the Army Ground Forces rejected their deployment as unnecessary. An attempt to upgrade the M4 Sherman by installing the 90 mm-armed turret from the T26 tank project on an M4 hull in April 1944 was halted after realizing it could not go into production sooner than the T26 and would likely delay T26 development.[64] Even in 1943, most German armored fighting vehicles (later models of the Panzer IV, StuG III, and Marder III) mounted the 7.5 cm KwK 40. As a result, even weakly armored light German tank destroyers such as the Marder III, which was meant to be a stop-gap measure to fight Soviet tanks in 1942, could destroy Shermans from a distance. The disparity in firepower between the German armored fighting vehicles that began to be fielded in 1943 and the 75 mm-armed M4 was the impetus to begin production of 76 mm-armed M4s in January 1944.[65] In testing prior to the invasion of Normandy, the 76 mm gun was found to have an undesirably large muzzle blast that kicked up dust from the ground and obscured vision for further firing. The M1A1C gun, which entered production lines in March 1944, was threaded for a muzzle brake, but as the brakes were still in development, the threads were protected with a cap. The addition of a muzzle brake on the new M1A2 gun (which also incorporated a faster rifling twist leading to a slight accuracy increase at longer ranges) beginning in October 1944 finally solved this problem by directing the blast sideways.[66]

Army doctrine at the time emphasized the multirole ability of the tank, and the capability of the high explosive shell was considered important. Being a dedicated anti-tank gun, the 76 mm had a much weaker high explosive shell than the existing 75 mm, and was not initially accepted by various U.S. armored division commanders, even though many had already been produced and were available. All of the U.S. Army M4s deployed initially in Normandy in June 1944 had the 75 mm gun.[67] Fighting against Panther tanks in Normandy quickly demonstrated the need for better anti-tank firepower, and the 76 mm M4s were deployed to First Army units in July 1944. Operation Cobra was the combat debut of the 76 mm gun-armed Sherman, in the form of the M4A1(76)W.[68] General George S. Patton's Third Army were initially issued 75 mm M4s and accepted 76 mm-armed M4s only after the Battle of Arracourt against Panther tanks in late September 1944.[69]

British Firefly in Namur, 1944. This is an M4 composite, showing the late cast hull front with large crew hatches

The higher-velocity 76 mm gun gave Shermans anti-tank firepower at least equal to most of the German vehicles they encountered, particularly the Panzer IV and StuG III. The gun could penetrate 125 mm (4.9 in) of unsloped RHA at 100 meters (110 yd) and 106 mm (4.2 in) at 1,000 meters (1,100 yd) using the usual M62 round.[70] The M1 helped to equalize the Sherman and the Panzer IV in terms of firepower; the 48-caliber 7.5 cm KwK 40 (75mm L/48) of the Panzer IV could penetrate 135 mm (5.3 in) of unsloped RHA at 100 meters (110 yd) and 109 mm (4.3 in) at 1,000 meters (1,100 yd). The 76 mm gun was still inferior to the much more powerful 70-caliber 7.5 cm KwK 42 (75mm L/70) of the Panther, which could penetrate 185 mm (7.3 in) of unsloped RHA at 100 meters (110 yd) and 149 mm (5.9 in) at 1,000 meters (1,100 yd) using the usual PzGr.39/42 round.[70] The 76 mm was capable of knocking out a Panther at normal combat ranges from the flanks or rear, but could not overcome the glacis plate. Due to its 55 degree slope, the Panther's 80 mm (3.1 in) glacis had a line of sight thickness of 140 mm (5.5 in) with actual effectiveness being even greater. An M4 might only knock out a Panther frontally from point-blank range by aiming for its turret front and transverse-cylindrical shaped mantlet, the lower edge of which on most Panthers (especially the earlier Ausf. D and A versions) constituted a vulnerable shot trap.[71] A 76 mm-armed Sherman could penetrate the upper frontal hull superstructure of a Tiger I tank from normal combat ranges. Although the new gun lessened the gap between the two tanks, the Tiger I was still capable of knocking an M4 out frontally from over 2,000 meters (2,200 yd).[72]

In late summer 1944, after breaking out of the bocage and moving into open country, U.S. tank units that engaged German defensive positions at longer ranges sometimes took 50% casualties before spotting where the fire was coming from.[73] The average combat range noted by the Americans for tank versus tank action was 800 to 900 meters (870 to 980 yd). Sherman crews also had concerns about firing from longer ranges, as the Sherman's high-flash powder made their shots easier to spot. This, and the U.S. Army's usual offensive tactical situation, often contributed to losses suffered by the U.S. Army in Europe.[74] Even though the various gunsights fitted to the Sherman had fewer magnification settings than those fitted to German tanks, their gunners were able to use a secondary periscope that featured a far larger field of view than their German counterparts.

T4 High-Velocity Armor Piercing (HVAP) ammunition became available in September 1944 for the 76 mm gun. The projectile contained a tungsten penetrator surrounded by a lightweight aluminum body and ballistic windshield, which gave it a higher velocity and more penetrating power. The increased penetration of HVAP allowed the 76 mm gun to match the Panther's 7.5 cm KwK 42 APCR shot.[75] However, its performance was heavily degraded by sloped armor such as the Panther's glacis. Because of tungsten shortages, HVAP rounds were constantly in short supply. Priority was given to U.S. tank destroyer units and over half of the 18,000 projectiles received were not compatible with the 76 mm gun M1, being fitted into the cartridge case of the M10 tank destroyer's 3-inch gun M7.[76] Most Shermans carried only a few rounds at any one time, and some units never received any.[77]

M4A2(76) HVSS with T23 turret and later 76 mm gun's muzzle brake; it also sports fenders, usually omitted on U.S. vehicles to ease maintenance

The British anticipated future developments in German armor and began development of a 3-inch (76 mm) antitank gun even before its 57 mm predecessor entered service. Out of expediency and also driven by delays in their new tank designs, they mounted the powerful 3 in (76 mm) Ordnance QF 17-pounder gun in a standard 75 mm M4 Sherman turret. This conversion became the Sherman Firefly. Like the U.S. M1 gun, the 17 pdr was also a 76 mm gun, but the British piece used a more voluminous cartridge case containing a much bigger propellant charge. This allowed it to penetrate 174 mm (6.9 in) of unsloped RHA at 100 meters (110 yd) and 150 mm (5.9 in) at 1,000 meters (1,100 yd) using APCBC ammunition.[70] The 17-pounder still could not penetrate the steeply sloped glacis plate of the Panther but it was expected to be able to pierce its gun mantlet at over 2,500 yards (2,300 m);[78] moreover it was estimated it would defeat the Tiger I's frontal armor from 1,900 yards (1,700 m).[79] However, British Army test results conducted with two Fireflys against a Panther turret-sized target demonstrated relatively poor accuracy at long range; a hit probability of 25.4% at 1,500 yards (1,400 m) with APCBC, and only 7.4% with APDS.[80] In late 1943, the British offered the 17-pounder to the U.S. Army for use in their M4 tanks. General Devers insisted on comparison tests between the 17-pounder and the U.S. 90 mm gun. The tests were finally done on March 25 and May 23, 1944; they seemed to show the 90 mm gun was equal to or better than the 17-pounder. By then, production of the 76 mm-armed M4 and the 90 mm-armed M36 were both underway and U.S. Army interest in the 17-pounder waned. Late in 1944, the British began to produce tungsten sabot rounds for the 17-pounder, which could readily breach the armor of even the Tiger II; these were not as accurate as standard rounds and not generally available.

After the heavy tank losses of the Battle of the Bulge, in January 1945, General Eisenhower asked that no more 75 mm M4s be sent to Europe: only 76 mm M4s were wanted.[81] Interest in mounting the British 17-pounder in U.S. Shermans flared anew. In February 1945, the U.S. Army began sending 75 mm M4s to England for conversion to the 17-pounder. Approximately 100 conversions were completed by the beginning of May. By then, the end of the war in Europe was clearly in sight, and the U.S. Army decided the logistical difficulties of adding a new ammunition caliber to the supply system was not warranted. None of the converted 17-pounder M4s were deployed in combat by the U.S., and it is unclear what happened to most of them, although some were given to the British as part of Lend-Lease post-war.[82]

General Lesley J. McNair was head of the Army Ground Forces from 1942 to 1944. McNair, a former artilleryman, advocated for the role of the tank destroyer (TD) within the U.S. Army. In McNair's opinion, tanks were to exploit breakthroughs and support infantry, while masses of attacking hostile tanks were to be engaged by tank destroyer units, which were composed of a mix of self-propelled and towed anti-tank guns. Self-propelled tank destroyers, called "gun motor carriages" (as were any U.S. Army self-propelled armored vehicles mounting an artillery piece of heavy caliber) were similar to tanks, but were lightly armored with open-topped turrets. The tank destroyers were supposed to be faster and carry a more powerful anti-tank gun than tanks (although in reality tanks often received more powerful guns before tank destroyers did) and armor was sacrificed for speed.[83] Armored Force and Tank Destroyer Force doctrine were developed separately, and it was not against Armored Force doctrine for friendly tanks to engage hostile tanks that appeared while attacking or defending.;[84] tank destroyers were to engage numbers of enemy tanks that broke through friendly lines.

McNair approved the 76 mm upgrade to the M4 Sherman and production of the 90 mm gun-armed M36 tank destroyer, but he at first staunchly opposed mass production of the T20 medium tank series and its descendants, the T25 and T26 (which would eventually become the M26 Pershing) during the crucial period of 1943 because they did not meet the two criteria of the Army Ground Forces for accepting new equipment; they were not "battle worthy," and he saw no "battle need" for them. In fall 1943, Lieutenant General Devers, commander of U.S. forces in the European Theater of Operations (ETO), asked for 250 T26 tanks for use in the invasion of France; McNair refused, citing the fact that he believed the M4 was adequate. Devers appealed all the way to the War Department, and Major General Russell L. Maxwell, the Assistant Chief of Staff G-4 of the War Department General Staff, ordered the 250 tanks built in December 1943. McNair finally relented in his opposition, but still opposed mass production; his Army Ground Forces even asked for the tanks to be "down-gunned" from 90 mm to 75 or 76 mm in April 1944, believing the 76 mm gun was capable of performing satisfactorily. Marshall then summarily ordered the tanks to be provided to the ETO as soon as possible. Soon after the Normandy invasion in June 1944, General Dwight D. Eisenhower urgently requested heavy tanks, but McNair's continued opposition to mass production due to persistent serious mechanical problems with the vehicles delayed their procurement. That same month, the War Department reversed course and completely overruled the Army Ground Forces when making their tank production plan for 1945. 7,800 tanks were to be built, of which 2,060 were to be T26s armed with 90 mm guns, 2,728 were to be T26s armed with 105 mm howitzers, and 3,000 were to be M4A3 Sherman tanks armed with 105 mm howitzers. As a part of the plan, the British requested 750 90 mm-armed T26s and 200 105 mm-armed T26s.[85] General McNair was killed in a botched air support mission in July 1944, and the path to production for the T26 tank became somewhat clearer. General Marshall intervened again and the tanks were eventually brought into full production. However, only a few T26 tanks (by then designated M26) saw combat beginning in February 1945, too late to have any effect on the battlefield.[86]

A USMC M4A3 uses its flame thrower during the Battle of Iwo Jima

The Sherman, like its M3 predecessor, was one of the first tanks to feature a gyroscopically stabilized gun and sight. The stabilization was only in the vertical plane, as the mechanism could not slew the turret. The stabilizer was sufficient to keep the gun's elevation setting within 1/8th of a degree, or 2 mils, while crossing moderately rough terrain at 15 miles per hour (24 km/h). This gave a hit probability of 70% on enemy tanks at ranges of 300 yards (270 m) to 1,200 yards (1,100 m).[87] The utility of the stabilization is debatable, with some saying it was useful for its intended purpose, others only for using the sights for stabilized viewing on the move.[88] Some operators disabled the stabilizer.

The 75 mm gun also had an effective canister round that functioned like a large shotgun. In the close fighting of the French bocage, the U.S. Army's 2nd Armored Division tanks used Culin Hedgerow Cutters fitted to their tanks to push three tanks together through a hedgerow. The flank tanks would clear the back of the hedgerow on their side with canister rounds while the center tank would engage and suppress known or suspected enemy positions on the next hedgerow. This approach permitted surprisingly fast progress through the very tough and well-defended hedgerows in Normandy. Over 500 sets of these were fitted to US armored vehicles, and many fitted to various British tanks (where they were called "prongs").

The 75 mm gun had a white phosphorus shell originally intended for use as an artillery marker to help with targeting. M4 tank crews discovered that the shell could also be used against the Tiger and Panther—when the burning white phosphorus adhered to the German tanks, their excellent optics would be blinded and the acrid smoke would get sucked inside the vehicle, making it difficult or impossible for the crew to breathe. This, and the fear of fire starting or spreading inside the tank, would sometimes cause the crew to abandon the tank.[89] There were several recorded instances where white phosphorus shells defeated German tanks in this fashion.[90]

A variant of the M4 Sherman was armed with the 105 mm M4 howitzer, which provided even more powerful high explosive armament. This variant was employed in three-vehicle "assault gun" platoons in tank battalions along with another 1 in each medium tank company (for a total of 6 per tank battalion)[91] to provide close fire support and smoke. Armored infantry battalions were also eventually issued three of these Shermans.[92] The 105 mm-armed variants were of limited use against enemy tanks due to the poor anti-armor performance of the howitzer, which was not intended to fight other tanks, though a high explosive anti-tank (HEAT) round for the 105 mm howitzer was available for self-defense.

The turret armor of the 75 mm and 105 mm-armed M4 ranged from 25.4 mm (1.00 in) to 76.2 mm (3.00 in) thick.[93] The turret front armor was 76.2 mm thick, angled at 30 degrees from the vertical, giving an effective thickness of 87.9 mm (3.46 in). The opening in the front of the M4's turret for the main gun was covered by a rounded 50.8 mm (2.00 in) thick rotor shield. Early Shermans that had a periscopic sight for the main gun mounted in the turret roof possessed a small 76.2 mm (3.00 in) thick mantlet that only covered the hole where the main gun barrel protruded; the exposed barrel of the coaxial machine gun was vulnerable to bullet splash or shrapnel and a small armored cover was manufactured to protect it. When the Sherman was later fitted with a telescopic sight next to the main gun, a larger 76.2 mm (3.00 in) thick gun mantlet that covered the entire rotor shield including the sight and coaxial machine gun barrel was produced.[93][94] 105 mm-armed Sherman tanks did not have a rotor shield, possessing only the mantlet to cover the opening in the turret front. The turret side armor was 50.8 mm (2.00 in) thick at a 5 degree angle from the vertical.[94] The turret rear armor was 50.8 mm (2.00 in) thick and vertical, while the turret roof armor was 25.4 mm (1.00 in) thick, and flat.[95]

Later models of the M4A1, M4A2 and M4A3 Sherman tanks were equipped with the T23 turret and the new 76 mm gun. This turret's armor was 63.5 mm (2.50 in) thick on the sides and rear, angled from 0 to 13 degrees from the vertical. It had a 25.4 mm (1.00 in) thick roof, which sat at 0 to 45 degrees from the vertical.[3] The front of the T23 turret, which like the 105 mm-armed Sherman's turret, did not have a rotor shield, was protected by an unsloped 88.9 mm (3.50 in) thick cast gun mantlet. Combat experience indicated that the single hatch in the three-man 75 mm gun turret was inadequate for timely evacuation, so Ordnance added a loader's hatch beside the commander's beginning in late 1943. All 76 mm gun turrets had two roof hatches.

The 1943 improvement program added patches of appliqué armor to the sides of the turret and hull. This Sherman also sports a Culin hedgerow cutter, a 1944 field improvisation for breaking through the thick hedgerows of the Normandy bocage

The Sherman's glacis plate was originally 50.8 mm (2.00 in) thick.[93][95] and angled at 56 degrees from the vertical, providing an effective thickness of 90.8 mm (3.57 in). The M4, M4A1, early production M4A2 and early production M4A3 possessed protruding cast "hatchway" structures that allowed the driver and assistant driver's hatches to fit in front of the turret ring. In these areas, the effect of the glacis plate's slope was greatly reduced. Later Shermans had an upgraded glacis plate that was uniformly 63.5 mm (2.50 in) thick and sloped at 47 degrees from the vertical, providing an effective thickness of 93.1 mm (3.67 in) over the entire plate. The new design improved overall ballistic protection by eliminating the "hatchways", while also allowing for larger hatches for the driver and bow gunner. The cast hull M4A1 for the most part retained its previous glacis shape even after the larger hatches were introduced; the casting, irrespective of the larger hatches, sat 37 to 55 degrees from the vertical, with the large majority of the piece sitting closer to a 55 degree angle.[3]

The transmission housing was rounded, made of three cast sections bolted together or cast as one piece. It ranged from 50.8–108 millimetres (2–4 ¹⁄₄ in) thick[95] The upper and lower hull sides were 38 mm (1.5 in) thick,[94][96] and vertical,[95] while the upper hull rear was also 38 mm (1.5 in) thick, vertical or sloped at 10 degrees from the vertical. The lower hull rear, which protected the engine, was 38 mm (1.5 in) thick, sloped at 0 to 22 degrees from the vertical depending upon the variant.[3] The hull roof was 25.4 mm (1.00 in).[95] The hull floor ranged from 25.4 mm (1.00 in) thick under the driver and assistant driver's positions to 12.7 mm (0.50 in) thick at the rear. The M4 had a hatch on the hull bottom to dispose of spent shell casings and to provide an emergency escape route. In the Pacific, Marines often used this Sherman feature in reverse to recover wounded infantry under fire.

The armor of the M4 was effective against most early war tank and anti-tank weapons,[93] but needed a compound angle to resist later German tank and anti-tank guns. The distinctive protruding "hatchways" of the early Sherman compromised the 56 degree-angled glacis plate, making them weak points where the effect of the glacis plate's slope was greatly reduced. In 1943, to make the thickness of these areas equal with the rest of the glacis plate, 1-inch thick (25 mm) appliqué armor plates were fitted in front of them.

A Waffenamt-Prüfwesen 1 report estimated[97] that with the M4 angled 30 degrees sidewards, the Sherman's glacis plate was invulnerable to shots from the Tiger's 8.8 cm KwK 36 L/56[98] and that the Panther, with its 7.5 cm KwK 42 L/70, would have to close in to 100 meters (110 yd) to achieve a penetration in the same situation.[99] Although the later-model German medium and heavy tanks were greatly feared, Buckley opined "The vast majority of German tanks encountered in Normandy were either inferior or merely equal to the Sherman."[100]

Research for tank casualties in Normandy from 6 June to 10 July 1944 conducted by the British No. 2 Operational Research concluded that, from a sample of 40 Sherman tanks, 33 tanks burned (82 percent) and 7 tanks remained unburned following an average of 1.89 penetrations. In comparison, from a sample of 5 Panzer IV's, 4 tanks burned (80 percent) and 1 tank remained unburned, following an average of 1.5 penetrations. The Panther tank burned 14 times (63 percent) from a sample of 22 tanks and following 3.24 penetrations, while the Tiger burned 4 times (80 percent) out of a sample of 5 tanks following 3.25 penetrations.[101] John Buckley, using a case study of the British 8th and 29th Armoured Brigades, found that of their 166 Shermans knocked out in combat during the Normandy campaign, 94 (56.6 percent) burned out. Buckley also notes that an American survey carried out concluded that 65% of tanks burned out after being penetrated.[102] United States Army research proved that the major reason for this was the stowage of main gun ammunition in the vulnerable sponsons above the tracks. A U.S. Army study in 1945 concluded that only 10–15 percent of wet stowage Shermans burned when penetrated, compared to 60–80 percent of the older dry-stowage Shermans.[103]

At first, a partial remedy to ammunition fires in the M4 was found in 1943 by welding 1-inch thick (25 mm) appliqué armor plates to the sponson sides over the ammunition stowage bins, though there was doubt that these had any effect. Later models moved ammunition stowage to the hull floor, with water jackets surrounding each stowage bin. The practice, known as "wet stowage", reduced the chance of fire after a hit to about 15 percent.[104] The Sherman gained grim nicknames like "Zippo" (after the cigarette lighter), and "Ronson" (because "it lights the first time, every time";[8] this story has been challenged on the grounds that the Ronson company did not begin using the slogan until the 1950s[105]) and "Tommycooker" (by the Germans, who referred to British soldiers as "Tommies"; a tommy cooker was a World War I-era trench stove). Fuel fires occasionally occurred, but such fires were far less common and less deadly than ammunition fires.[103] In many cases, the fuel tank of the Sherman was found intact after a fire. Tankers described "fierce, blinding jets of flame", which is inconsistent with gasoline-related fires.[102]

Upgrades included the rectangular armor patches protecting ammunition stowage mentioned above, and smaller armor patches in front of each of the protruding hatchway structures in the glacis in an attempt to mitigate their ballistic weakness. Field improvisations included placing sandbags, spare track links, concrete, wire mesh, or even wood for increased protection against shaped-charge rounds. While mounting sandbags around a tank had little effect against high-velocity anti-tank gunfire it was thought to provide standoff protection against HEAT weapons, primarily the German Panzerfaust anti-tank grenade launcher and the bazooka-derived Panzerschreck 88 mm calibre anti-tank rocket launcher. In the only study known to have been done to test the use of sandbags, on March 9, 1945, officers of the 1st Armored Group tested standard Panzerfaust 60s against sandbagged M4s; shots against the side blew away the sandbags and still penetrated the side armor, whereas shots fired at an angle against the front plate blew away some of the sandbags but failed to penetrate the armor. Earlier, in the summer of 1944, General Patton, informed by his ordnance officers that sandbags were useless and that the machines' chassis suffered from the extra weight, had forbidden the use of sandbags. Following the clamor for better armor and firepower after the losses of the Battle of the Bulge, Patton ordered extra armor plates salvaged from knocked-out American and German tanks welded to the turrets and hulls of tanks of his command. Approximately 36 of these up-armored M4s were supplied to each of the three armored divisions of the Third Army in the spring of 1945.[106]

M4A3E2 Sherman Jumbo. Many units replaced the original 75 mm gun with a 76 mm gun

The M4A3E2 Sherman "Jumbo" assault tank variant, based upon a standard M4A3(75)W hull, had an additional 38 mm (1.5 in) plate welded to the glacis, giving a total thickness of 101.6 mm (4.0 in), which resulted in a glacis of 148.97 mm (5.9 in) line-of-sight thickness, and over 180 mm (7.1 in) effective thickness.[107] The sponson sides had 38 mm (1.5 in) thick plates welded on, to make them 76 mm (3.0 in) thick. The transmission cover was significantly thicker, and a new, more massive T23-style turret with 177.8 mm (7.0 in) of armor on the sides and rear and a 25.4 mm (1 in) thick flat roof, and a gun mantlet with an additional 88.9 mm (3.5 in) of armor welded on, which resulted in a thickness of 177.8 mm, was fitted. It was originally to be armed with the 76 mm gun, but the 75 mm was preferred for infantry support and was used, although some were later upgraded to use the 76. The higher weight required changing the transmission gear ratios to reduce maximum speed to 22 mph, and crews were warned not to let the suspension "bottom" too violently. 254 were built at the Fisher Tank Arsenal from May to July 1944, and arrived in Europe in the fall of 1944, being employed throughout the remainder of the fighting in various roles. They were considered "highly successful".[108]