The 76 mm gun M1 was an American World War II–era tank gun developed by the United States Ordnance Department in 1942 to supplement the 75 mm gun on the basic Medium tank M4. It was also used to arm the M18 Hellcat tank destroyer.
Although the gun was tested in early August 1942 and classified on 18 August 1942, it was not until August 1943Zaloga 2003, page 6 that the Ordnance Department developed a mounting for the M4 tank that the tank forces would accept. It was not accepted for combat until July 1944. In January 1943, the decision was made to mount the 76 mm on the vehicle that would become the M18.Zaloga 2004, page 7 By May 1944, it was being combat tested as the T70.Zaloga 2004, page 14 The gun would be replaced upon the 90 mm entering service.
Design and development Before the United States had battle experience against heavily armored German tanks, the development of a weapon superior to the 75 mm gun was anticipated. The original Ordnance Department specifications of 11 September 1941 for the M4 tank allowed for the mounting of numerous weapons including the 3 inch gun.Hunnicutt 1978, page 198 The first specimens of the weapon that was to become the 76 mm Gun M1 were being evaluated in August 1942 while the U.S. did not enter the ground war in the European-African-Middle Eastern region until Operation Torch in November 1942.
The 3 inch gun, based on the 3-inch gun M1918 anti-aircraft gun, was considered too large and heavy at about Hunnicutt 1978, page 563 for mounting in the M4 tank. New stronger steels Green 1955, page 237 were used to create a weapon of similar performance weighing about .Hunnicutt 1978, page 564 It was a new gun with a breech similar to that of the 75 mm M3 Gun but with a new tube (barrel and cartridge chamber) design to accommodate a new cartridge. It fired the same projectiles as the 3-inch Gun M1918 M7 gun mounted on the 3in Gun Motor Carriage M10 tank destroyer and towed 3-inch Gun M5 anti-tank gun, but from a different cartridge case. The "76-mm" designation was chosen to help keep the supply of ammunition from being confused between the two guns.Zaloga 2003, page 4 The 76 mm also differed in that successive models received a muzzle brake and faster rifle twist.
Aberdeen Proving Ground began evaluations of the first test guns, designated the T1, around 1 August 1942.Hunnicutt 1978, page 199 The first test guns had a bore length of 57 calibers and when tested on an M4 tank; it was found that the long barrel caused balance problems. Another T1 test gun was produced with the barrel shortened to 52 calibers and a counterweight added to the breech guard to improve balance.
By 17 August, the Ordnance Department had classified the test gun with the shorter barrel as the 76-mm M1 Hunnicutt 1978, page 200 picture caption and set up the precedent for the designation of M4 tanks armed with the gun to include "(76M1)".Hunnicutt 1978, page 200
Tests of production M1 guns revealed that the gun with its counterweight also had issues with binding when trying to rotate the turret when the tank was resting at a steep angle. An storage box was added to the turret rear to improve balance, with evaluations held in early 1943 and the final report tendered in April 1943.Hunnicutt 1978, page 202 This worked, but was rejected by the Armored Force due to the turret being cramped.
A more satisfactory mounting was found in August 1943 by utilizing the turret design of the T23 tank on the M4 chassis to carry the 76 mm gun.Hunnicutt 1978, page 204 The 76 mm M1A1 version of the gun was then created, having a longer recoil surface to also help with balance by permitting the placement of the trunnions further to the front.
Production and tactical doctrine By August 1943, the M4 tank armed with the 76 mm gun in the modified T23 turret was finally ready for production. A proposal was made by the Armored Force for a test run of 1,000 tanks for combat trials and, if that was successful, then devoting all M4 tank manufacturing capacity to those armed with the 76 mm gun. This was changed to a rate that would equip 1/3 of the M4 tanks with the 76 mm gun.Zaloga 2003, page 8
The production proposal was part of a memo in September 1943 pointing out various flaws of the gun that made it less desirable for tank use: muzzle blast, a weaker high explosive shell, more awkward ammunition handling, and ammunition storage. Summed up, the 76 mm offered about of added armor penetrating power for a loss of some high explosive firepower.Zaloga 2008, page 116 In a meeting in April 1944 held to discuss the assignment of the first production M4(76M1) tanks received in Britain to units, a presentation comparing the 76 mm to the 75 mm went over similar points, adding that the 76 mm was more accurate, but did not yet have an appropriate smoke round.
Muzzle blast The muzzle blast of early 76 mm guns obscured the target with smoke and dust. This could prevent the gunner from seeing where the projectile struck. The Ordnance Department initially reduced the amount of smoke by using a long primer that gave a more complete burn of the propellant before it exited the barrel.Hunnicutt 1978, page 206 The revised ammunition began to be issued for use in August 1944.Zaloga 2003, page 18 Muzzle brakes, that redirected the blast left and right, were tested in January 1944 and authorized in February 1944, with production starting in June 1944. Mid-production guns (M1A1C) were threaded for a muzzle brake, with the threads covered by a protector cap.Zaloga 2004, page 13 Enough muzzle brakes were produced to allow them to be released onto M4 production lines in the fall.
For those vehicles that did not have a muzzle brake, once the Armored Force began to accept M4s, it was recommended that tank commanders stand outside the tank and "spot" the strike of rounds to guide the gunner.
High-explosive capacity The situation with the high-explosive shell was that the 3 inch M42 projectile for the 76 mm gun carried a filler of about of explosives while the 75 mm gun M48 high explosive projectile carried .Ordnance Department 1944, pages 356, 359 Far more high explosive ammunition was used by tankers than armor piercing types, the proportions being about 70% HE, 20% AP and 10% smoke overall,Zaloga 2003, page 7 The ratio could vary by unit: From 3 August – 31 December 1944, the 13th Tank Battalion fired 55 rounds of M62 APC-T armor piercing versus 19,634 rounds of M42 high explosive.Green 2007, page 118
Types of ammunition (AP) The 76mm had many variations of ammunition, like the M62 APCBC, it weighed 11.2kg (24.8lb), and traveled up to 792m/s (2600ft/s). The 76mm also had a M93 HVAP shell available, which at point blanck could penetrate 201-218mm (8.6in) at 0 degrees, and from 2000 meters, 132mm (5.2in) The 76mm had an option for a M79 AP solid shot round, at point blank, it could penetrate 129mm at 0 degrees, and at 2000 meters, 85mm of penetration, all for RHA.
Smoke ammunition The M88 smoke round for the 76 mm provided a "curtain" of smoke. The tankers found the 75 mm M64 WP (White Phosphorus) smoke projectile useful not only for providing smoke coverage but also attacking targets including enemy tanks.Green 2007, page 81 using the wrong designation "M89" Some units equipped with the 76 mm preferred to maintain a 75 mm armed tank on hand to provide the M88 WP projectile.Zaloga 1978, pages 37-38
Round size It was thought that the longer and heavier 76 mm might impede handling inside the tank's turret, slowing the rate of fire. This may have been more of a concern than was warranted: on 22 April 1945, the crew of an M4 76 mm crew encountered an unidentified vehicle – which was actually a British scout car – in an ambush position, and the "76 roared twice in rapid succession". The British gunner stated that his vehicle had been destroyed, "before I could lay my hand on the trigger".Hunnicutt 1978, page 322
It was also thought that the longer 76 mm would reduce ammunition capacity. The 76 mm was first tested on the M4A1 series tank which carried 90 rounds of 75 mm ammunition,Hunnicutt 1978, page 540 while most other models carried 97 rounds of 75 mm.Hunnicutt 1978, pages 538, 542, 544, 549 The 76 mm cartridge reduced this to 83 rounds. By late 1943, the Army had adopted the wet storage system of water containers among the rounds, to reduce fires and for the 76 mm gun this provided 71 rounds of ammunition, while the 75 mm could carry 104 rounds.Hunnicutt 1978, pages 260, 261 Storage depended on organization: The 76-mm T72 Gun Motor Carriage, designed to mount the 76-mm on the M10 GMC chassis in a T23 turret lightened for the job, carried 99 rounds (but not in wet storage).Hunnicutt 1978, page 376
Operational history US service The 76 mm gun saw first use in a test batch of M18 Hellcat gun motor carriages in Italy in May 1944, under their development designation T70.Zaloga 2004, page 14 The moderate performance of the 76 mm gun by 1944 standards was one of three reasons the plans for M18 production were cut from 8,986 to 2,507, of which 650 were converted to unarmed utility vehicles.Zaloga 2004, page 12 An experiment was performed mounting the 90-mm armed M36 turret on an M18 to provide more firepower than the 76-mm.Zaloga 2004, page 38
The first M4 tanks armed with 76 mm guns intended for combat were produced in January 1944.Zaloga 2003, page 10 Tanks equipped with the gun began arriving in Britain in April 1944.Zaloga 2003, page 12 The issue with muzzle blast had not been addressed and higher-level commanders had doubts about the use of, let alone need for, the new weapon. The medium-velocity 75 mm M3 gun, which first armed the standard M4 Sherman, was quite capable of dealing with most of the German armored fighting vehicles met in 1942 and 1943, and had better high explosive capability and fewer issues with muzzle blast. It was not until July 1944 that a call for M4s armed with 76 mm guns was put out in France after unexpectedly high losses by US tank units and the arrival of numerous Panther tanks on the US sector of the front.
Deliveries of the 76-mm armed tanks lagged such that by January 1945 they made up only 25% of the tanks in Europe. Plans were made by field units to directly replace the 75s on some tanks using a weight welded to the turret rear to balance it. A prototype was built, but the supply of ready-made tanks increased and that project ended.Zaloga 2003, page 33
The 75 mm armed M4 tanks were never completely replaced during the war with some units in Europe still had about a 50/50 mix.Zaloga 2003, page 22 Units in Italy readily accepted the 76 mm,Zaloga 2003, page 36 but were never shipped as many as desired. The US units in the Pacific Theater relied mainly on the 75 mm gun.Zaloga 2003, page 37 The 76 mm-armed M18 did see use in the Pacific late in the war.Zaloga 2004, page 34
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