76 mm gun M1

76 mm gun M1

An M18 Hellcat armed with a 76 mm gun
Type Tank gun
Place of origin United States
Service history
Used by United States
Wars World War II
Specifications
Caliber 76 millimetres (3.0 in)

The 76 mm gun M1 was an American World War II–era tank gun used to supplemented the 75 mm gun on the basic Medium tank M4s, and was used for all 76 mm Gun Motor Carriage M18 tank destroyers. The medium-velocity 75 mm M3 L/37.5 gun, which armed the standard M4 Sherman, was designed as a dual purpose weapon. Although it was quite capable of dealing with the initially 30 mm to 50 mm thick frontal armor of German Panzer IV tanks and StuG III assault guns, the subsequent uparmoring of these vehicles to 80 mm and upgunning to the 7.5 cm KwK 40 made it more of a match for the Sherman. The appearance of the Panther and Tiger tanks on the battlefield diminished the ability of the Sherman to engage enemy tanks at long distances.[1] As a result, a higher velocity weapon was demanded.

Design and development

Development of a better weapon than the 75-mm gun was foreseen before the U.S. had experience with well-armored German vehicles. The original Military specifications of 11 September 1941 for the M4 tank allowed for the mounting of numerous weapons including the 3-inch gun then in development.[2] The 3-inch gun was considered too heavy (at about 1,990 lb (900 kg).[2] New stronger steels [3] were used to create a weapon weighing about 1,200 lb (540 kg).[2] The development of the 76-mm gun for tests started on 20 August 1942 and the 76-mm M1 was standardized on September 10.[3] The U.S. entered the ground war in the European/Africa region in November 1942 via Operation Torch.

It was a new gun with a breech similar to that of the 75 mm M3 Gun. It fired the same projectiles as the 3-inch (76 mm) 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 was developed as a lighter gun than the "3 inch". The gun received a muzzle brake and faster rifle twist during production.

While the 76 mm had less High Explosive (HE) and smoke performance than the 75 mm, the higher-velocity 76 mm gave better anti-tank performance, with firepower similar to many of the armored fighting vehicles it encountered, particularly the Panzer IV and StuG vehicles. Using the M62 APC round, the 76mm gun penetrated 109 mm (4.3 in) of armor at 0° obliquity and 1,000 m (3,300 ft), with a muzzle velocity of 792 m/s (2,600 ft/s). The HVAP round was able to penetrate 178 mm (7.0 in) at 1,000 m (3,300 ft), with a muzzle velocity of 1,036 m/s (3,400 ft/s).[4]

The first test gun had a bore length of 57 calibers and was designated the T1. When it was tested on an M4 Sherman tank, it was then found that the long barrel caused balance problems. Another test gun was produced with the barrel shortened and a counterweight added to the breech to compensate. The reduction in length (by about 15 inches) did not reduce performance; penetration figures remained the same.[5] The shorter barrel was maintained when the cannon was finally adopted as the 76-mm M1.[2]

When the counterweight was found to be insufficient, an 800 pound storage box was added to the turret rear. This worked but was rejected as too much of an expedient, the turret being cramped. A more satisfactory mounting was found by utilising the turret design of the T23 tank on the M4 chassis to carry the 76mm gun. The 76-mm M1A1 version of the cannon was created, having a longer recoil surface to also help with balance by permitting the placement of the trunions further up front.[2]

Wholesale introduction of the 76 mm gun was opposed due to its inferior HE round—approximately 0.9 lb (0.41 kg) of explosive to the 1.5 lb (0.68 kg) in the 75 mm round—and the muzzle blast which could create large dust clouds in dry conditions.[6] Later production guns were given a muzzle brake to deflect the blast sideways (M1A1C and M1A2).

Alternates to the 76-mn M1

The 76-mm M1 was not the preferred weapon of 1944 it was the only alternate to the 75-mm available to US tank forced despite several suggestions by various entities for other weapons.

The Aberdeen based Ballistics Research Laboratory suggested that research into arming the M4 medium tank with the 90-mm gun (if need be by altering the cartridge case and gun) be pursued as well as a 3-inch gun firing a 15 lb (6.8 kg) shot at 915 m/s (3,000 ft/s). The Armored Board suggested the production of 1,000 M4 medium tanks armed with 90-mm guns in the fall of 1943. [2]

The British expressed interest in mountin their 17-pounder on the M4 in August 1943, offering a monthly alottment of 200 weapons and ammunition, which could begin 3 months following acceptance. By the time the US took this up in 1944 the British were too busy with their own conversions.[7]

The UK was not interested in the 76 mm gun Sherman as they had their own guns and tanks under development. Although only slightly longer at 55 calibers, their Ordnance QF 17 pounder (76.2 mm) anti-tank gun had a much larger cartridge case which used about 5.5 lb (2.5 kg) more propellant. Developed as an expediency, M4 Shermans converted to use the 17pdr were known as the Sherman Firefly.

The anti tank performance of the 76mm was inferior to the British 17 pounder, and even more so if the latter was using discarding sabot rounds, though with that ammunition the 17pdr was less accurate than the 76mm.

Variants

Usage

A T23 turret used on 76 mm gunned Shermans, here without the muzzle brake

With British Commonwealth designations in parentheses:

76 mm gunned Shermans supplied to the British were only used in Italy or by the Polish 1st Armoured Division in North-West Europe. The British supported their 75 mm gunned Shermans with QF 17 pdr (76mm) equipped "Fireflies"

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 number T70.[8]

The first M4 tanks armed with 76-mms intended for combat were produced in January 1944. Tanks equipped with the cannon began arriving in Britain in April 1944. 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. It was not until July 1944 that a call for M4s armed with 76s was put out in France after unexpectedly high losses by US tank units. [7]

Deliveries of the 76-mm armed tanks lagged in part due to tank losses forcing the shipping of more 75-mm armed tanks . 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. [7]

The 75-mm armed M4 tanks were never completely replaced during the war with some units in Europe still having about a 50/50 mix. Units in Italy readily accepted the 76-mm but were never shipped as many as desired. The US units in the Pacific relied mainly on the 75-mm gun.[7]

Towed variant

From 1943, at the instigation of the head of the Armored Force General Jacob Devers, US Ordnance worked on a towed anti-tank gun based on the barrel of the M1, known as "76 mm gun T2 on carriage T3". Later interest in the project declined and in 1945 the program was officially canceled.[9]

Performance

Penetration of armor at 30 degrees from vertical at two ranges
Ammunition 500 m 1,000 m
Armour-Piercing Capped (APC), US M62 93 mm[2] 88 mm[2]
Armour-Piercing (AP), US M79 109 mm,[2][10] 92 mm[2]
Armour-Piercing Capped Ballistic Capped (APCBC)[11] 98–93 mm[12] 88 mm[12]
High-Velocity Armour-Piercing (HVAP)[12] 139 mm[11] 127 mm[11]
High-Velocity Armour-Piercing M93[2] 157 mm[2] 135 mm[2]
High-Velocity Armour-Piercing T-4[10] 147 mm 120 mm

Penetration comparison

Penetration figures (90 degrees) uses American and British 50% success criteria,
and allowing direct comparison to foreign gun performance.[13]
Ammunition typeMuzzle velocity
(m/s)		Penetration (mm)
100 m 250 m 500 m 750 m 1000 m 1250 m 1500 m 1750 m 2000 m 2500 m 3000 m
M62 792 m/s (2,600 ft/s) 125 121 116 111 106 101 97 93 89 81 74
M79 792 m/s (2,600 ft/s) 154 145 131 119 107 97 88 79 72 59 48
M93 1,036 m/s (3,400 ft/s) 239 227 208 191 175 160 147 135 124 108 88

See also

Weapons of comparable role, performance and era

Notes

    1. ↑ Jentz, Thomas; Doyle, Hilary (2001). Panzerkampfwagen IV Ausf.G, H and J 1942-45. Osprey Publishing. p. 20. ISBN 1841761834.
    2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 R.P. Hunnicutt (1978). Sherman: A History of the American Medium Tank.
    3. 1 2 Green, Constance; Thomson, Harry; Roots, Peter (1955). The Ordnance Department : Planning Munitions for War CMH Pub 10-9. Center for Military History.
    4. ↑ Zaloga, Steven. T-34-85 vs. M26 Pershing: Korea 1950. London: Osprey Publishing, 2010. pp. 32-33.
    5. ↑ Honner, David. "USA Guns 75mm and 76mm calibre". Guns Vs Armor.
    6. ↑ M4 (76mm) Sherman Medium Tank 1943–65, p. 7.
    7. 1 2 3 4 Zaloga, Steven (2003). M4 (76mm) Sherman Tank 1943-65. Osprey Publishing. ISBN 9781841765426.
    8. ↑ M18 Hellcat Tank Destroyer 1943–73, Zaloga 2004 p. 13.
    9. ↑ Steven J. Zaloga, Brian Delf. US Anti-tank Artillery 1941–45. Osprey Publishing, 2005 (New Vanguard 107). ISBN 1-84176-690-9. page 20.
    10. 1 2 Steven J. Zaloga. and Peter Sarson (1993). Sherman Medium Tank.
    11. 1 2 3 Bovington Tank Museum (1975). Fire and Movement.
    12. 1 2 3 Harry Woodman (1991). Tank Armament in World War Two.
    13. ↑ Bird, Lorrin Rexford; Livingston, Robert D. (2001). WWII Ballistics: Armor and Gunnery. Overmatch Press. p. 63.

    Further reading

    ==External links==p

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