M4 Sherman

U.S. design prototype

The U.S. 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 tried by the British in Africa against early German tanks, 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 the British army weapons in their entirety the American designers were prepared to accept proved British ideas. British ideas, as embodied with in a tank designed by the Canadian General Staff, also influenced the development of the American Sherman tank. Before long American Services and designers had accumulated sufficient experience to forge ahead on several points. In the field of tank armament the American 75mm and 76mm dual-purpose tank guns won the acknowledgement of British tank experts. Detailed design characteristics for the M4 were submitted by the Ordnance Department on 31 August 1940, but 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 became the Sherman.

The Sherman's reliability resulted from many features developed for U.S. light tanks during the 1930s, including vertical volute spring suspension, rubber-bushed tracks, and a rear-mounted radial engine with drive sprockets in front. The goals were to produce a fast, dependable medium tank able to support infantry, provide breakthrough striking capacity, and defeat any tank then in use by the Axis nations.

The T6 prototype was completed on 2 September 1941. The T6 upper hull was a single large casting. It featured a side hatch, and a single overhead hatch for the driver. 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 bow gunner. The modified T6 was standardized as the M4, and production began in February 1942

Doctrine

As the United States approached entry in 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.

The M4 was, therefore, not originally intended as an infantry support tank; in fact, FM 100-5 specifically stated the opposite. It placed tanks in the "striking echelon" of the armored division, and placed the infantry in the "support echelon". A field manual covering the use of the Sherman (FM 17–33, "The Tank Battalion, Light and Medium" of September 1942) devoted one page of text and four diagrams to tank-versus-tank action, out of 142 pages. 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 anti-tank work was primarily to be done by towed and self-propelled anti-tank guns, both of which were referred to as 'tank destroyers'. 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.

U.S. production history

The first production began with the Lima Locomotive Works on the assembly line set for tanks for British use. The first production Sherman was given over to the US Army for evaluation and it was the second tank of the British order that went to London. Named Michael probably after Michael Dewar, head of the British tank mission in the U.S., it was displayed in London and is now an exhibit at The Tank Museum, Bovington, UK.

In World War II, the U.S. Army ultimately fielded 16 armored divisions, along with 70 independent tank battalions, while the U.S. Marine Corps fielded six independent Sherman tank battalions. A third of all Army tank battalions, and all six Marine tank battalions, were deployed to the Pacific Theater of Operations (PTO). Prior to September 1942, President Franklin D. Roosevelt had announced a production program calling for 120,000 tanks for the Allied war effort, which would have created 61 armored divisions. Although the American industrial complex was not affected by enemy aerial bombing nor submarine warfare as was Japan, Germany and, to a lesser degree, Great Britain, an enormous amount of steel for tank production had been 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.

The Army had seven main sub-designations for M4 variants during production: M4, M4A1, M4A2, M4A3, M4A4, M4A5, and M4A6. These designations did not necessarily indicate linear improvement; in that "M4A4" did not indicate it was better than "M4A3." These sub-types indicated standardized production variations, which were in fact often manufactured concurrently at different locations. The sub-types differed mainly in engines, although the M4A1 differed from the other variants by its fully cast upper hull, with a distinctive rounded appearance. The M4A4 had a longer engine system that required a longer hull and more track blocks, and thus the most distinguishing feature of the M4A4 was the wider longitudinal spacing between the bogies. M4A5 was an administrative placeholder designation for Canadian production. The M4A6 had a radial diesel engine and elongated chassis, but only 75 of these were ever produced.

While most Shermans ran on gasoline, the M4A2 and M4A6 had diesel engines. The M4A2 was powered by a pair of GMC 6–71 two-stroke straight six engines, the M4A6 using a Caterpillar D-200A radial producing some 450 hp (340 kW) at 2,000 rpm, adapted from the "RD-1820" experimental diesel version of Wright Aeronautical's mass-produced Cyclone 9 aviation radial. These, plus the M4A4, which used the Chrysler A57 multibank engine, were mostly supplied to other Allied countries under Lend-Lease. "M4" can refer specifically to the initial sub-type with its Continental radial engine (R-975), or generically, to the entire family of seven Sherman sub-types, depending on context. Many details of production, shape, strength, and performance improved while in production, without a change to the tank's basic model number. These included more durable suspension units, safer "wet" (W) ammunition stowage, and stronger or more efficient armor arrangements, such as the M4 Composite, which had a cast front hull section mated to a welded rear hull. British nomenclature differed from that employed by the U.S.

A 24-volt electrical system was used in the M4.

Early Shermans mounted a 75mm medium-velocity general-purpose gun. Although Ordnance began work on the Medium Tank T20 as a Sherman replacement, ultimately the Army decided to minimize production disruption by incorporating elements of other tank designs into the Sherman. Later M4A1, M4A2, and M4A3 models received the larger T23 turret with a high-velocity 76 mm gun, which reduced the number of high-explosive and smoke rounds carried and increased the number of anti-tank rounds. Later, the M4 and M4A3 were factory-produced with a 105 mm howitzer and a distinctive rounded mantlet, which surrounded the main gun, on the turret. 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. The first Sherman 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, far better protected T23-style turret, in order to assault fortifications. The M4A3 model was the first to be factory-produced with the horizontal volute spring suspension (HVSS) system, beginning in September 1944. With wider tracks to distribute weight, and 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).

The M4 Sherman's basic chassis was used for all the sundry roles of a modern mechanized force: roughly 50,000 Sherman tanks, plus thousands more derivative vehicles under different model numbers. These included the M10 Wolverine and M36 tank destroyers; M7B1, M12, M40, and M43 self-propelled artillery; the M32 and M74 "tow truck"-style recovery tanks with winches, booms, and an 81 mm mortar for smoke screens; and the M34 (from M32B1) and M35 (from M10A1) artillery prime movers.

Allocation

During World War II, approximately 19,247 Shermans were issued to the US Army and about 1,114 to the US Marine Corps. 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 and an estimated 812 were transferred to China. 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.

First combat

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.

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.

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

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 late 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, 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.

Pacific Theater

While combat in the European Theater of Operations (ETO) 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 US Army fielded 16 armored divisions and 70 independent tank battalions during the war, only a third of the battalions and none of the divisions were deployed to the Pacific Theater. The Imperial Japanese Army (IJA) deployed only their 2nd Tank Division to the Pacific during the war. 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.

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. 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. The Chinese in India received 100 M4 Shermans and used them to great effect in the subsequent 1943 and 1944 offensives.

To counter the Sherman, 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-3's and two Type-4's were built and none saw combat; they were saved for the defense of the Japanese homeland, leaving 1930s vintage light and medium tanks to do battle against 1940s built medium Allied armor.

During these latter years of the war, General Purpose High Explosive (HE) ammunition was preferred, 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 the tank destroyers were useful for penetrating fortifications, M4s armed with flamethrowers were often deployed, as direct fire seldom destroyed Japanese fortifications.

Post–World War II

After World War II, the U.S. kept the M4A3 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. Despite no longer being the primary U.S. tank, 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, although the use of High Velocity Armor Piercing shells, advanced optics and better crew training gave the Sherman an advantage. The M4A3(76)W HVSS Sherman, using 76 mm HVAP ammunition, destroyed a total of 41 enemy tanks from July–November 1950. The lighter M4A3(76)W HVSS tank became the preferred US tank in the later phases of the Korean conflict, due to the mechanical reliability of the M4, its ease of maintenance, and its driveability compared to the M26 tank.

The U.S. Army replaced the M4 with M46 Pattons, an improved M26, during the 1950s. 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 acquired a single M4A2 lacking a 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(105mm)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 75mm guns and components whenever these became available, composing a large part of Israeli tank forces for the next eight years. The 75mm-armed Sherman were replaced by M4A1(76mm) Shermans imported from France before the 1956 Suez Crisis, after it was realised that their armour penetration was insufficient for combat against newer tanks such as the Centurions and 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 M4A1E8 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.

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.

Armament

The gun on the original M4 was the short-barreled medium-velocity 75 mm M3 gun. When it first saw combat in North Africa in late 1942 against the Panzer III and Panzer IV, the Sherman's gun could penetrate the armor of these tanks within 1,000 yd (910 m). U.S. Army Intelligence discounted the arrival of the Tiger I in late 1942 and the Panther tank in 1943, predicting that the Panther would be a heavy tank like the Tiger, and doubted that many would be produced. There were also reports of relatively small caliber British QF 6 pdr (57 mm) guns being able to destroy the Tiger. However, this was only happening 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. The tests of the 76 mm were later ruled inaccurate, 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 make the Panther the standard tank of their panzer divisions in 1944, supported by some Tigers.

Despite the Bureau of Ordnance development of new 76 mm and 90 mm anti-tank guns, the Army Ground Forces rejected their deployment on U.S. tanks as unnecessary. 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 of 1943 and the 75 mm-armed M4 was the impetus to begin production of 76 mm-armed M4s in April 1944. However, transfer of the tanks to the front started slowly, and most tanks still had 75 mm M3 guns, even by Operation Cobra in July 1944; Cobra was also the debut of the 76mm gun-armed Shermans, in the form of M4A1(76)W Shermans.

The 76 mm gun could penetrate some 98 mm (3.9 in) of unsloped face hardened armor plate at 2,000 meters (2,200 yd) using M62 APCBC ammunition, about twice the average tank engagement range noted by the Canadians. This was enough to reliably penetrate a Panzer IV's glacis, which offered a maximum of about 87 mm (3.4 in) of protection. However, the 76 mm was not powerful enough against the upper glacis of a Panther. Due to its 55 degree angle, the Panther's 80 mm (3.1 in) upper glacis had a line of sight thickness of 140 mm (5.5 in) with actual effectiveness being even greater. Utilizing standard M79 armor-piercing shot, an M4 might only knock out a Panther frontally from point-blank ranges. Therefore, Shermans had to aim for the Panther's weaker turret and standard, 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 as-designed. A 76 mm-armed Sherman could penetrate the upper frontal hull superstructure of a Tiger I heavy tank from 400 meters (440 yd); although this lessened the gap between the tanks, the Tiger I was capable of knocking a M4 out frontally from over 2,000 meters (2,200 yd). Sherman crews also had concerns about firing from longer ranges, as the Sherman's high-flash powder made their shots easier to spot. Their gun sights were fixed magnification, while German tanks had multiple magnification settings. Sherman gunners did have the use of a secondary sight which allowed them a larger field of view over their German counterparts. However, this advantage was mostly useful in close range situations due to lack of magnification. In summer 1944, after breaking out of the bocage and moving into open country, U.S. tank units which engaged German defensive positions at longer ranges sometimes took 50% casualties before spotting where the fire was coming from.

The Sherman was first equipped with the 75 mm M3 Gun, a 40-caliber long gun which could penetrate 87 mm (3.4 in) of unsloped rolled homogeneous armor at 100 meters (110 yd) and 70 mm (2.8 in) at 1,000 meters (1,100 yd) firing the usual M61 round. The average combat range noted by the Americans for tank vs. tank action was 800 meters (870 yd) to 900 meters (980 yd). Conditions later in the war necessitated up-gunning to the 76 mm gun M1A1, M1A1C, or M1A2, a 52-caliber long gun which could penetrate 143 mm (5.6 in) of unsloped rolled homogeneous armor at 100 meters (110 yd) and 97 mm (3.8 in) at 1,000 meters (1,100 yd) using the usual M79 round. The M1 helped to equalize the Sherman and the Panzer IV in terms of firepower. The KwK 42 of the Panther could penetrate 185 mm (7.3 in) 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. The British-developed Sherman Firefly was an M4 re-gunned with their own, 3-inch (76.2 mm) caliber QF 17 pounder anti-tank gun. Like the U.S. gun, The 17 pdr was also 76 mm gun, but the British piece used a much longer 76.2×583mmR round, containing a much bigger propulsive charge which allowed it to penetrate 140 mm (5.5 in) (of RHA sloped at 30 degrees) at 100 meters (110 yd) and 120 mm (4.7 in) at 1,000 meters (1,100 yd) using APC Mk.IV shot. The 17-pounder gun allowed the Firefly a firepower equal to that of the Panther, (even more so with APDS ammunition) and the capability to easily destroy a Tiger tank. The muzzle flash due to unburnt powder from the increased charge could leave crews momentarily blinded after firing.

The tank destroyer doctrine

General Lesley J. McNair was head of Army Ground Forces. McNair, a former artilleryman, championed the tank destroyer (TD) within the U.S. Armored Forces. Tanks were to support the infantry, and exploit breakthroughs. Enemy tanks were to be engaged by the tank destroyer force, which was composed of a mix of self-propelled tank destroyers and towed anti-tank guns, but it was not against armor doctrine for tanks to engage enemy tanks. The tank destroyers were to engage enemy tanks that broke through friendly lines. U.S. tank destroyers, called "gun motor carriages" (as were any US 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; armor was sacrificed for speed.

McNair approved the 76 mm upgrade to the M4 Sherman and production of the 90 mm gun-armed M36 tank destroyer, but he staunchly opposed development of the T26 and other proposed heavy tanks during the crucial period of 1943 because he saw no "battle need" for them.

In mid-1943, Lt. General Devers, commander of U.S. forces in the European Theater of Operations (ETO), asked for 250 T26s for use in the invasion of France. McNair refused. Devers appealed to General George Marshall, the Army Chief of Staff. Marshall summarily ordered the tanks to be provided to the ETO as soon as they could be produced. Soon after the Normandy invasion, General Dwight D. Eisenhower urgently requested heavy tanks (now designated M26 Pershing), but McNair's continued opposition delayed production. General Marshall intervened again and the tanks were eventually brought into production. However, only a few saw combat beginning about February 25, 1945, too late to have any effect on the battlefield.

Gun development

When the original 76 mm gun, known as the T1, was first installed in the M4 turret, it was found to unbalance the turret, and the gun barrel was also thought to protrude too far forward, making it more difficult to transport and susceptible to hitting the ground on undulating terrain. Army Ordnance reduced the barrel length 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, along with a modified version of the gun known as the M1A1.

Although tests against armor plate suggested that the new M1A1 gun would be adequate, testing against captured Panther tanks was never done. This would have shown the gun could penetrate the gun mantlet and possibly the glacis of the Panther only at point blank or very close ranges. In practice, this meant that, despite both the Panther and Sherman being classed and produced as "medium tanks" by their respective forces, the Panther was basically invincible in frontal engagements against the Sherman at anything but point blank range.

The 90 mm gun M3 developed by U.S. Ordnance could not be easily installed on the M4, but was installed on the open-topped M36 tank destroyer and was the main gun for the T26 tank project (which eventually became the M26 Pershing). An attempt to upgrade the M4 Sherman by installing the 90 mm T26 turret on a M4A3 hull in April 1944 was halted after realizing it could not go into production sooner than the T26 and would likely delay T26 development.

In testing prior to the invasion of Normandy, the new 76 mm gun on the M4 Sherman was found to have an undesirably large muzzle blast that kicked up dust from the ground and obscured vision for further firing. The muzzle of 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) beginning in October 1944 finally solved this problem by directing the blast sideways. The 76 mm gun also had a much weaker high-explosive shell than the existing 75 mm gun. Standard Army doctrine at the time emphasized the importance of the infantry support role of the tank, and the high-explosive round was considered more important. Hence the 76 mm M4 was not initially accepted by various U.S. armored division commanders, even though a number 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.

The British were more astute in their anticipation of the future development of German armor—beginning development of a 3-inch (76 mm) anti-tank gun even before its 57 mm predecessor entered service and planning for its use in tanks that would replace the M4. Out of expediency driven by delays in their new tank designs, they mounted the high-powered 3 in (76 mm) Ordnance QF 17-pounder gun in a standard 75 mm M4 Sherman turret. This conversion became the Sherman Firefly. The 17-pounder still could not penetrate the 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); moreover it was estimated it would defeat the Tiger I's frontal armor from 1,900 yards (1,700 m). However, British Army test results conducted with two Fireflys against a Panther turret-sized target demonstrated a hit probability of 25.4% at 1,500 yards (1,400 m) with APCBC, and only 7.4% with APDS. Late in 1944, the British began to produce tungsten-cored 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.

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 (even though the 17-pounder could be mounted in a standard M4 turret while the 90 mm gun needed a new design). 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 M4 and the 90 mm M36 were both underway and U.S. Army interest in the 17-pounder waned.

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. General George S. Patton's Third Army were initially issued 75 mm M4s and accepted 76 mm M4 Shermans only after the Battle of Arracourt against Panther tanks in late September 1944.

High-Velocity Armor Piercing (HVAP) ammunition, standardized as M93, became available in August 1944 for the 76 mm gun. The projectile contained a tungsten core penetrator surrounded by a lightweight aluminum body, 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. However, its performance was heavily degraded by sloped armor such as the Panther's glacis, which was immune to HVAP rounds necessitating shots to be aimed at the mantlet and turret front. Because of tungsten shortages, HVAP rounds were constantly in short supply. Priority was given to U.S. tank destroyer units; most Shermans carried only a few rounds and some units never received any.

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.

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 train 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.

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. However, with regular M79 AP (armor-piercing) ammunition, the 76 mm could knock out a Panther only at point blank range with a shot to the upper glacis, at close range with a shot to its mantlet, or at long range with a shot its flank. At long range, the Sherman was outmatched by the Panther's high velocity 75 mm gun, which could easily penetrate the Sherman's armor from all angles. This, and the U.S. Army's usual offensive tactical situation, often contributed to losses suffered by the U.S. Army in Europe.

The M4 was criticized by its crews for inability to pivot turn (turn in place), limiting its usefulness in urban warfare against pivot-turning Panthers. This deficiency was partially compensated by the faster traverse of its turret.

Variants

The Sherman, like its M3 predecessor, was an early tank 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). 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. Some operators disabled the stabilizer.

The 75 mm gun also had an effective canister round that functioned as a large shotgun. In the close fighting of the French bocage, the U.S. Army's Hell on Wheels 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 fire starting or spreading inside the tank, would sometimes cause the crew to abandon the tank. There were several recorded instances where white phosphorus shells defeated German tanks in this fashion.

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 six-vehicle "assault gun" platoons in tank battalions to provide close fire support and smoke. Armored infantry battalions were also issued three of these Shermans. 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.

Turret

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. The turret front armor was 76.2 mm (3.0 in) thick, angled at 30 degrees from the vertical. The front of the M4's turret was also protected by a 50.8 mm (2.00 in) thick rotor shield, (on 75 mm-armed tanks only) along with a 76.2 mm (3.00 in) thick rounded gun mantlet The turret side armor was 50.8 mm (2.00 in) at a 5 degree angle from the vertical. 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. Later models of the M4A1, M4A2 and M4A3 Sherman tanks were equipped with the T23 turret and new 76 mm gun. This turret was 63.5 mm (2.50 in) thick on the sides and rear, with a 25.4 mm (1.00 in) thick roof which sat at 0 to 45 degrees from the vertical. 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 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.

Hull

The glacis was 50.8 mm (2.00 in) thick. The Sherman's glacis was originally angled at 56 degrees in the "small hatch" variants, possessing protruding "hatchway" structures. Later Shermans had an upgraded glacis plate that was 63.5 mm (2.50 in) thick and sloped at 47 degrees from the vertical; the cast hull M4A1 for the most part retained its previous glacis shape; the plate, irrespective of the larger hatches, sat 37 to 55 degrees from the vertical, with the large majority of the plate sitting closer to a 55 degree angle. The new design slightly improved ballistic protection while also allowing for larger hatches for the driver and bow gunner.

The transmission housing was cast in one piece or made of three cast sections bolted together, ranging from 50.8–108 mm (2 to 4.25 in) thick The upper and lower hull sides were 38 mm (1.5 in) thick, and vertical, while the upper hull rear was also 38 mm (1.5 in) thick, but sloped at 10 degrees from the vertical on most variants. The lower hull rear, which protected the engine, was 38 mm (1.5 in) thick, 0 to 22 degrees from the vertical depending on the variant. The hull roof was 25.4 mm (1.00 in). 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 used this Sherman feature in reverse to recover wounded infantry under fire.

Effectiveness

The armor of the M4 was effective against most early war anti-tank weapons, but needed a compound angle to resist later German tank and anti-tank guns. Standard production versions of the Sherman, the welded hull M4, M4A2 and early production M4A3, had protruding armored "hatchways" located just in front of the driver and assistant driver that compromised the 56 degree-angled glacis plate, making them weak points where the effect of the glacis plate's slope was greatly reduced. The KwK 40 7.5 cm L/48 tank gun that armed late war versions of the Panzer IV could penetrate a Sherman's armor up to a range of 1,370–1,500 meters, and larger guns could penetrate past 2,000 meters (2,200 yd). Regardless of this vulnerability, historian John Buckley has stated the M4 was "moderately superior" to the relatively small but older Panzer IV. A Waffenamt-Prüfwesen 1 report estimated that with the M4 angled 30 degrees sidewards, the Sherman's glacis was invulnerable to the Tiger's 8.8 cm KwK 36 L/56 and that the Panther with its 7.5 cm KwK 42 L/70 would have to close in to 100 meters (110 yd) in the same situation. Although the later-model 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."

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 up (82%) 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 up (80%) and 1 tank remained unburned, following an average of 1.5 penetrations. The Panther tank burned up 14 times (63%) from a sample of 22 tanks and following 3.24 penetrations, while the Tiger burned up 4 times (80%) out of a sample of 5 tanks following 3.25 penetrations. 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%) were burnt out. Buckley also notes that an American survey carried out concluded that 65% of tanks burnt out after being penetrated. United States Army research proved that the major reason for this was the stowage of main gun ammunition in the 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.

At first, a partial remedy to ammunition fires in the M4 was found 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 additional water jackets surrounding the main gun ammunition stowage. The practice, known as wet stowage, reduced the chance of fire after a hit to about 15%. The Sherman gained grim nicknames like "Tommycooker" (by the Germans, who referred to British soldiers as "Tommies"; a tommy cooker was a World War I-era trench stove). The British and Germans took to calling it the "Ronson", after the lighter. Fuel fires occasionally occurred, but such fires were far less common and less deadly than ammunition fires. 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.

Upgrades

Upgrades included rectangular armor patches on each side protecting ammunition stowage, and smaller armor patches in front of each of the protruding hatchway structures in the glacis. 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 Panzerschreck 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.

M4A3E2

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 (4.00 in), which resulted in a glacis 148.97 mm (5.865 in) thick LOS, and over 180 mm (7.1 in) effective thickness. The sponson sides had an extra 38 mm (1.5 in) plate welded on, to make them 76 mm (3.0 in) thick, a significantly thicker transmission casing, a new, more massive T23-style turret with 177.8 mm (7.00 in) of armor on the sides and rear and a 25.4 mm (1.00 in) thick flat roof, and a gun mantlet with an additional 88.9 mm (3.50 in) of armor welded on which resulted in a thickness of 177.8 mm (7.00 in). Intended for the assault to break out of the Normandy beachhead, it was originally to be armed with the 76 mm gun, but the 75 mm was preferred for infantry support and was used. The higher weight required reducing 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".

Mobility

In its initial specifications for a replacement for the M3 Medium Tank, the U.S. Army restricted the Sherman's height, width, and weight so that it could be transported via typical bridges, roads, railroads and landing craft without special accommodation. This greatly aided the strategic, logistical, and tactical flexibility and mobility of all Allied armored forces using the Sherman.

The Sherman had good speed both on- and off-road. Off-road performance varied. In the desert, the Sherman's rubber-block tracks performed well; while in the confined, hilly terrain of Italy, the Sherman could often cross terrain that some German tanks could not.

Albert Speer recounted in his autobiography Inside the Third Reich

On the southwestern front (Italy) reports on the cross country mobility of the Sherman have been very favorable. The Sherman climbs mountains our tank experts consider inaccessible to tanks. One great advantage is that the Sherman has a very powerful motor in proportion to its weight. Its cross-country mobility on level ground is, as the 26th Panzer Division reports, definitely superior to that of our tanks

However, while this may have held true compared with the first generation German tanks, such as the Panzer III and Panzer IV, comparative testing with the second generation German tanks (Panther and Tiger) conducted by the Germans at their Kummersdorf testing facility, as well as by the U.S. 2nd Armored Division, proved otherwise.

Lieutenant Colonel Wilson M. Hawkins of the 2nd AD wrote the following comparing the US M4 Sherman and German Panther in a report to Allied headquarters:

It has been claimed that our tank is the more maneuverable. In recent tests we put a captured German Mark V [Panther] against all models of our own. The German tank was the faster, both across country and on the highway and could make sharper turns. It was also the better hill climber.

This was backed up in an interview with Technical Sergeant Willard D. May of the 2nd AD who commented:

I have taken instructions on the Mark V [Panther] and have found, first, it is easily as maneuverable as the Sherman; second the flotation (ability to avoid bogging down) exceeds that of the Sherman.

Staff Sergeant and Tank Platoon Sergeant Charles A. Carden completes the comparison in his report:

The Mark V [Panther] and VI [Tiger] in my opinion have more maneuverability and certainly more flotation. I have seen in many cases where the Mark V and VI tanks could maneuver nicely over ground where the M4 would bog down. On one occasion I saw at least 10 Royal Tigers [Tiger II] make a counter attack against us over ground that for us was nearly impassable.

U.S. crews found that on soft ground such as mud or snow, the narrow tracks gave poor (i.e., high) ground pressure compared to wide-tracked second-generation German tanks such as the Panther and the Tiger. The U.S. Army issued extended end connectors, or "duckbills", to add width to the standard tracks as a stopgap solution. Duckbills began to reach front-line tank battalions in July 1944, and were original factory equipment for the heavy M4A3E2 Jumbo to compensate for the extra weight of armor. The M4A3(76)W HVSS Shermans and other late models with wider-tracked HVSS suspension and twinned road wheels on each axle – rather than the single road wheel of the VVSS suspension designs – corrected these problems but formed only a small proportion of the tanks in service even in 1945.

U.S. variants

Vehicles that used the M4 chassis or hull:

Foreign variants and use

The Sherman was extensively supplied through Lend-Lease to Britain, the Soviet Union and the Free French. Britain received 17,287 Shermans of various models. The Soviet Union received 4,035 M4A2 Shermans. The Free French was the third largest recipient, taking 657 Shermans 1943-1944. 57 Shermans were delivered to other nations.

A similar vehicle was developed in Canada from January 1941, the Ram tank. Like the Sherman, this developed the M3 chassis and powertrain, with a fully rotating turret. One improvement was the use of all-steel 'CDP' (Canadian Dry Pin) tracks, which although an inch narrower than the early M4 steel and rubber pad tracks, were cheaper to produce and gave better traction. Suspension units and roadwheels remained the M3 vertical volute pattern, with the idler above the mounting bracket, rather than the M4 development with the idler moved behind the mounting bracket to give more room for suspension travel. The Ram had a distinctive turret with a bolted flat-faced mantlet and the UK 6 pdr gun, with the hull machine gunner housed in a rotating turret based on the M3 'Lee' cupola, rather than the simpler ball-mount that was becoming universal for tank hull guns. Production facilities for the Ram were constructed at the Montreal Locomotive Works, with the aid of ALCO, but the large armour castings for turret and hull were supplied by General Steel Castings in the US. Greater Sherman production and availability meant that the Ram was never used in action as a gun tank, being either used for training or converted to Kangaroo armoured personnel carriers.

A later Canadian medium tank, produced from late 1943, was the Grizzly, an adaption of the Sherman M4A1. This differed only in details, such as the CDP tracks, British radio equipment and the British 2" smoke mortar in the turret roof. 188 were produced.

After World War II, Shermans were supplied to some NATO armies; Shermans were used by U.S. and allied forces in the Korean War.

Shermans also went to Israel. The Israeli up-gunned 75 mm M-50 and 105 mm armed M-51 Super Shermans are remarkable examples of how a long obsolete design can be upgraded for front-line use. They saw combat in the 1967 Six-Day War, fighting Soviet World War II-era armor like the T34/85, and also in the 1973 Yom Kippur War, proving effective even against newer, heavier Soviet tanks like the T-54 and T-55.