76 mm gun M1
American tank gun
|76 mm gun M1|
An M18 Hellcat armed with a 76 mm gun
|Place of origin||United States|
|Used by||United States|
|Wars||World War II, Korea|
|Designer||US Ordnance Department|
|Mass||1,141 lb (517.55 kg)|
|Barrel length||52 calibres|
|Shell||Fixed QF 76.2×539mm R|
|Caliber||76.2 millimetres (3.00 in)|
The 76 mm gun M1 was an American World War II–era tank gun developed by the U.S Ordnance Department in 1942 to supplement the 75 mm gun on the basic Medium tank M4. It was also used to arm the M18 Hellcattank destroyer.
Although the gun was tested in early August 1942 and classified on August 17, 1942, it was not until August 1943 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. By May 1944, it was being combat tested as the T70.
Design and development
The development of a better weapon than the 75 mm gun was foreseen before the U.S. had combat experience with well-armored German tanks. 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. 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 1,990 lb (900 kg) for mounting in the M4 tank. New stronger steels  were used to create a weapon of similar performance weighing about 1,200 lb (540 kg). 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 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" designation was chosen to help keep the supply of ammunition from being confused between the two guns. 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 August 1, 1942. 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 August 17, the Ordnance Department had classified the test gun with the shorter barrel as the 76-mm M1  and set up the precedent for the designation of M4 tanks armed with the gun to include "(76M1)".
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 800 lb (360 kg) 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. 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. 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.
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 1 inch (25 millimetres) of added armor penetrating power for a possible loss of some high explosive firepower. 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.
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. The revised ammunition began to be issued for use in August 1944. 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. 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.
The situation with the high-explosive shell was that the 3 inch M42 projectile for the 76 mm gun carried a filler of about 0.9 lb (0.41 kg) of explosives while the 75 mm gun M48 high explosive projectile carried 1.5 lb (0.68 kg). Far more high explosive ammunition was used by tankers than armor penetrating types, the ratio being about 70% HE, 20% AP and 10% smoke overall, The ratio could vary by unit: From August 3 to December 31, 1944 the 13th Tank Battalion fired 55 rounds of M62 APC-T armor piercing versus 19,634 rounds of M42 high explosive.
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. Some units equipped with the 76 mm preferred to maintain a 75 mm armed tank on hand to provide the M88 WP projectile.
It was thought that the longer and heavier 76 mm might hamper handling inside the tank's turret, slowing the rate of fire. This may have been more of a concern than was warranted: on April 22, 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".
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, while most other models carried 97 rounds of 75 mm. 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. 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).
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. 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. An experiment was performed mounting the 90-mm armed M36 turret on an M18 to provide more firepower than the 76-mm.
The first M4 tanks armed with 76 mm guns intended for combat were produced in January 1944. Tanks equipped with the gun 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. 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.
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. Units in Italy readily accepted the 76 mm, but were never shipped as many as desired. The US units in the Pacific Theater relied mainly on the 75 mm gun. The 76 mm-armed M18 did see use in the Pacific late in the war.
Crew members of destroyed M4A3 tanks reported direct hits with 76 mm tank fire bouncing off turret and front slope plates of enemy tank, which is further proof of inability of present medium tanks to successfully fight the German Mark VI tank.
Unit History, 781st Tank Battalion p 9 of 47, 1945-01-19
Ordnance told me this 76 would take care of anything the Germans had. Now I find you can’t knock out a damn thing with it.
— General Dwight D. Eisenhower
The 76 mm M1, while an improvement over the previous 75 mm, was a disappointment in its promised performance vis-à-vis the Panther tank and upgraded models of the Panzer IV H/J in the frontal arcs. This was the case of the 76 mm M1 versus the frontal armor of these tanks only. The other arcs did not present a problem. The cause of this was the M62A1 APC round issued with the gun. Another issue surfaces on detailed analysis with a change induced by the problem with the M18 turret and the weight of the original 76/57 development gun. The problem is that the M18 turret was strained by the forward weight of the barrel. In production, the 76mm M1 was shortened to 52 calibers to address this issue. The result was a loss in velocity and this also affected the anti-armor performance of the shell. In response to the lack of performance and displeasure expressed at high levels at the lack of performance, a new shell was developed. The 76 mm M93 High-Velocity, Armor-Piercing Tracer (HVAP-T) was a large improvement being an Armor Piercing Composite Rigid shot, where the full bore, lightweight outer shell contained a slug of tungsten alloy. This improved velocity, thus penetration, but the APCR slowed faster than the AP shot or APHE shell, such that penetration dropped below that of the previous two rounds at around 1,500 yards. The American APCR data seems to indicate that US designs were superior to German and their Soviet copies in retaining their velocity to longer ranges. The US Army did not adopt the APDS shot until the middle 1950s as the British designs had significant dispersion problems from point of aim, being less accurate. In the ETO the determination of the effective range of engagements between armor fell into at or under 890 yards. The shell brought the Panzer IV turret penetration to 1,850 yards. The Panther remained immune in the frontal arc. The side and rear arcs remained vulnerable out to 2,500 yards.
The UK had developed a more effective anti-tank gun before the 76 mm gun became widely available. Although only slightly longer at 55 calibers, their Ordnance QF 17 pounder (76.2 mm) anti-tank gun had a much larger 76.2×583mmR cartridge case, which used about 5.5 lb (2.5 kg) more propellant. The anti-tank performance of the 76 mm was inferior to the British 17-pounder, more so if the latter was using APDS discarding sabot rounds, though with that ammunition the 17-pounder was less accurate than the 76 mm. The 17-pounder was also much larger and had a longer recoil than the 76 mm, which required a redesign of the turret and despite this, made the turret very cramped. The 17-pounder also had a less effective HE round. The 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 and Commonwealth units in north-west Europe supported their 75 mm gunned Shermans with 17-pounder armed Sherman Fireflies.
The first 76-mm-armed Shermans started to reach Red Army units in late summer 1944. In 1945, some units were standardized to depend mostly on them, transferring their T-34s to other units. Parts of the Polish First Army also briefly used M4A2 (76 mm) tanks, borrowed from the Red Army after heavy losses in the conquest of Danzig.
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After World War II
By the end of 1950, more than 500 76mm gun M4A3E8 tanks were in Korea. These 76 mm-armed Shermans served well in the Korean War and, having better crew training and gun optics, had little problem piercing the armor of North Korean-manned T-34/85 tanks when firing HVAP rounds, which were amply supplied to units. Some 76 mm-armed M4s  and M18s were distributed around the world and used by other countries post-war. The 76 mm gun was sometimes replaced by a more powerful weapon in service with other nations after World War II.
France delivered 76 mm-gunned Sherman tanks to Israel which used them in Operation Kadesh in 1956 and in the 1967 Six day war, particularly in the conquest of Jerusalem. Some were still used as dozer tanks in the Yom Kippur War in 1973.
Some M4A3E4s, retrofitted with the M1A1 76 mm gun, as well as a few M18s, were used by various sides during the civil conflicts of former Yugoslavia during the 1990s.
India and Pakistan
Pakistan bought 547 M4A1E6(76)s during the 1950s and used them in 1965 and 1971 Indo-Pakistani Wars with neighbouring India, which also fielded Sherman tanks (M4A3E4s) as well.
Uganda purchased a few ex-Israeli M4A1(76)Ws and used them during the Idi Amin regime up until the Ugandan-Tanzanian War.
- T1: Originally 57 calibers long gun, reduced to 52 calibers after tests in effort to improve balance
- M1: 52 calibers long version of gun adopted for use 
- M1A1: M1 with longer recoil surface to allow it to be mounted on trunions placed 12 inches further forward
- M1A1C: M1A1 threaded for muzzle brake 
- M1A2: M1A1C with rifling twist changed from 1:40 calibers to 1:32 calibers
A muzzle brake was tested in January 1944, authorized in February 1944 with production starting June 1944. Not all guns received them. The threads of those without a brake were covered by a protector visible in many pictures.
Proposed 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 the program was officially cancelled in 1945.
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 tank and StuG assault gun vehicles. Using the M62 APC round, the 76 mm gun penetrated 109 mm (4.3 in) of armor at 0° obliquity at 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).
|Projectile||Complete round||Projectile weight||Filler/core||Muzzle velocity||Range|
|M42A1 HE||22.11 lb (10.03 kg)||12.87 lb (5.84 kg)||0.86 lb (0.39 kg)||2,700 ft/s (820 m/s)||14,650 yd (13,400 m)|
|M62A1 APC||24.55 lb (11.14 kg)||15.43 lb (7.00 kg)||0.144 lb (0.065 kg)||2,600 ft/s (790 m/s)||16,100 yd (14,700 m)|
|M79 AP||24.24 lb (11.00 kg)||15 lb (6.8 kg)||None||2,600 ft/s (790 m/s)||12,770 yd (11,680 m)|
|M88 Smoke||13.43 lb (6.09 kg)||7.6 lb (3.4 kg)||3.3 lb (1.5 kg)||900 ft/s (270 m/s)||2,000 yd (1,800 m)|
|T4 (M93) HVAP (APCR)||7.6 lb (3.4 kg)||3.9 lb (1.8 kg)||3,400 ft/s (1,000 m/s)|
The M42A1 High Explosive shell contained a 0.86 lb (0.39 kg) explosive filler of TNT or a 0.85 lb (0.39 kg) mixture of 0.08 lb (0.036 kg) of cast TNT and 0.77 lb (0.35 kg) 50/50 Amatol. A reduced charge load existed with a velocity of 1,550 ft/s (470 m/s) and range of 8,805 yd (8,051 m).
The standard M62A1 Armor Piercing Capped projectile was of the APCBC design.
The substitute standard M79 Armor Piercing solid monobloc shot had no filler, windscreen, or penetrating cap.
The M88 H.C. B.I. Smoke Shell contained a filler of H.C. Based on a British design, it was intended to provide a slow-release "curtain" of smoke versus the exploding white phosphorus shell available to the 75-mm and other cannon originally designed for artillery spotting but which could also cause damaging burns.
The M26 brass cartridge case was used for all loaded rounds, with a weight of 5.28 lb (2.39 kg) and length of 21.3 in (54 cm). It was an entirely different case from the 3-inch MKIIM2 case used for the 3-inch M3 anti-aircraft gun and 3-inch M5, M6, and M7 guns used on the a towed anti-tank gun, M6 heavy tank, and M10 Gun Motor Carriage. The 76-mm chamber capacity varied by projectile (also given is the capacities for similar 3-inch rounds to illustrate the size differences):
|Gun||M42 HE||M62 APC||M79 AP||M88 H.C. B.I.|
|76-mm M1||140.5 cu in (2,302 cc)||142.6 cu in (2,337 cc)||143.66 cu in (2,354.2 cc)||143.6 cu in (2,353 cc)|
|3-inch M3/5/6/7||203.5 cu in (3,335 cc)||205.585 cu in (3,368.93 cc)||203.5 cu in (3,335 cc)||None|
The 3 inch cartridge was not completely filled by the propellants used; a distance wad was used to keep the propellant pressed against the primer end. By way of comparison the 75 mm M3 gun had a chamber capacity of about 88 cu in (1,440 cc) for the M61 armor piercing projectile and about 80 cu in (1,300 cc) for the M48 high explosive projectile  and the British 17pdr 300 cu in (4,900 cc).
Vehicles mounting the 76 mm
With British Commonwealth designations in parentheses:
|Ammunition type||Muzzle velocity|
|100 m||250 m||500 m||750 m||1000 m||1250 m||1500 m||1750 m||2000 m||2500 m||3000 m|
|M62 versus FHA||792 m/s (2,600 ft/s)||124||123||122||119||116||113||110||105||101||92||83|
|M62 versus RHA||792 m/s (2,600 ft/s)||125||121||116||111||106||101||97||93||89||81||74|
|M79 versus FHA||792 m/s (2,600 ft/s)||132||124||112||101||92||83||75||68||62||50||41|
|M79 versus RHA||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|
Similar, alternative weapons
The 76 mm M1 was a project initiated by the Ordnance Department itself. Various entities suggested other weapon options which were not pursued.
- In October 1942, the Aberdeen-based Ballistics Research Laboratory suggested that research begin into two options: (1) arming the M4 medium tank with the 90 mm gun (if need be by altering the cartridge case and gun) and (2) designing a 3-inch gun firing a 15 lb (6.8 kg) shot at 915 m/s (3,000 ft/s).
- The Armored Board (the Armored Forces evaluation center at Fort Knox) suggested the production of 1,000 M4 medium tanks armed with 90-mm guns in the fall of 1943.
- The British expressed interest in mounting their 17-pounder on the M4 in August 1943, offering a monthly allotment of 200 weapons and ammunition, which could begin three months following acceptance. By the time that the US took this up in 1944, the British were too busy with their own conversions resulting in the Sherman Firefly. Some conversions destined for the US Army were performed in 1945 but did not see combat.
Weapons of comparable role, performance and era
- ^ abcdeHunnicutt 1978, p. 200
- ^ abcZaloga 2003, p. 6
- ^ abcZaloga 2003, p. 16
- ^Zaloga 2004, p. 7
- ^Zaloga 2004, p 14
- ^ abcdefgHunnicutt 1978, p. 198
- ^Hunnicutt 1978, p.563
- ^Green 1955, p. 237
- ^ abcdefghHunnicutt 1978, p. 564
- ^Zaloga 2003, p. 4
- ^ abcHunnicutt 1978, p. 199
- ^Hunnicutt 1978, p. 200 picture caption
- ^ abHunnicutt 1978, p. 202
- ^ abcHunnicutt 1978, p. 204
- ^Zaloga 2003, p. 8
- ^ abcdZaloga 2008, p. 116
- ^ abcdZaloga 2003, p. 12
- ^ abcHunnicutt 1978, p. 206
- ^Zaloga 2003, p. 18
- ^ abZaloga 2004, p. 13
- ^Ordnance Department 1944, p. 356, 359
- ^Zaloga 2003, p. 7
- ^Green 2007, p. 118
- ^ abcLeventhal 1996, p 288
- ^Green 2007, p. 81 using the wrong designation "M89"
- ^Zaloga 1978, p. 37-38
- ^Hunnicutt 1978, p. 322
- ^Hunnicutt 1978, p. 540
- ^Hunnicutt 1978, p. 538, 542, 544, 549
- ^Hunnicutt 1978, p. 260, 261
- ^ abHunnicutt 1978, p. 376
- ^Zaloga 2004, p. 14
- ^Zaloga 2004, p. 12
- ^Zaloga 2004, p. 38
- ^Zaloga 2003, p. 10
- ^Zaloga 2003, p. 33
- ^Zaloga 2003, p. 22
- ^Zaloga 2003, p. 36
- ^ abZaloga 2003, p. 35
- ^Zaloga 2003, p. 37
- ^Zaloga 2004, p. 34
- ^ abZaloga 2003, p. 42
- ^Zaloga 2003, p. 39
- ^ abZaloga 2003, p. 41
- ^Hunnicutt 1978, p. 207
- ^Zaloga 2005, p. 20
- ^Zaloga, Steven. T-34-85 vs. M26 Pershing: Korea 1950. London: Osprey Publishing, 2010. pp. 32-33.
- ^ abcdefLeventhal 1996, p 287
- ^Ordnance Department 1944, p. 128
- ^Ordnance Department 1944, p. 124
- ^ abOrdnance Department 1944, p. 132
- ^Leventhal 1996, p 283,284
- ^Hunnicutt 1978, p.562
- ^Hunnicutt 1978, p.565
- ^ abSteven J. Zaloga. and Peter Sarson (1993). Sherman Medium Tank.
- ^ abcBovington Tank Museum (1975). Fire and Movement.
- ^ abcHarry Woodman (1991). Tank Armament in World War Two.
- ^Bird, Lorrin Rexford; Livingston, Robert D. (2001). WWII Ballistics: Armor and Gunnery. Overmatch Press. p. 63.
- ^ abHunnicutt 1978, p. 212
- ^Zaloga 2003, p. 9
- Green, Constance; Thomson, Harry; Roots, Peter (1955). The Ordnance Department: Planning Munitions for War CMH Pub 10-9. Center for Military History.
- Green, Michael; Brown, James (2007). M4 Sherman at War. Zenith Press. ISBN .
- Hunnicutt, R.P. (1978). Sherman: A History of the American Medium Tank. Echo Point Books and Media, LLC. ISBN .
- Leventhal, Lionel (1996). The American Arsenal. Greenhill Books, London. Stockpile Books, Pennsylvania. ISBN .
- Ordnance Department, United States (1944). TM 9-1901 Artillery Ammunition June 1944. War Department.}
- Zaloga, Steven (1993). Sherman Medium Tank 1942-45. New Vanguard 3. Osprey Publishing. ISBN .
- Zaloga, Steven (2003). M4 (76mm) Sherman Tank 1943-65. New Vanguard 73. Osprey Publishing. ISBN .
- Zaloga, Steven (2004). M18 Hellcat Tank Destroyer 1943-97. New Vanguard 97. Osprey Publishing. ISBN .
- Zaloga, Steven (2005). US Anti-tank Artillery 1941–45. New Vanguard 107. Osprey Publishing. ISBN .
- Zaloga, Steven (2008). Armored Thunderbolt: The U.S. Army Sherman in World War II. Stackpole Books. ISBN .
- TM 9-308
- SNL C-46
- SNL C-58
- SNL C-64
Kinetic energy penetrator
High density non-explosive projectile
A kinetic energy penetrator (KEP, KE weapon, long-rod penetrator or LRP) is a type of ammunition designed to penetratevehicle armour using a flechette-like, high-sectional densityprojectile. Like a bullet, this type of ammunition does not contain explosive payloads and uses purely kinetic energy to penetrate the target. Modern KEP munitions are typically of the armour-piercing fin-stabilized discarding sabot (APFSDS) type.
Early cannons fired kinetic energy ammunition, initially consisting of heavy balls of worked stone and later of dense metals. From the beginning, combining high muzzle energy with projectile weight and hardness have been the foremost factors in the design of such weapons. Similarly, the foremost purpose of such weapons has generally been to defeat protective shells of armored vehicles or other defensive structures, whether it is stone walls, sailship timbers, or modern tank armour. Kinetic energy ammunition, in its various forms, has consistently been the choice for those weapons due to the highly focused terminal ballistics.
The development of the modern KE penetrator combines two aspects of artillery design: high muzzle velocity and concentrated force. High muzzle velocity is achieved by using a projectile with a low mass and large base area in the gun barrel. Firing a small-diameter projectile wrapped in a lightweight outer shell, called a sabot, raises the muzzle velocity. Once the shell clears the barrel, the sabot is no longer needed and falls off in pieces. This leaves the projectile traveling at high velocity with a smaller cross-sectional area and reduced aerodynamic drag during the flight to the target (see external ballistics and terminal ballistics). Germany developed modern sabots under the name "treibspiegel" ("thrust mirror") to give extra altitude to its anti-aircraft guns during the Second World War. Before this, primitive wooden sabots had been used for centuries in the form of a wooden plug attached to or breech loaded before cannonballs in the barrel, placed between the propellant charge and the projectile. The name "sabot" (pronounced SAB-oh in English usage) is the French word for clog (a wooden shoe traditionally worn in some European countries).
Concentration of force into a smaller area was initially attained by replacing the single metal (usually steel) shot with a composite shot using two metals, a heavy core (based on tungsten) inside a lighter metal outer shell. These designs were known as armour-piercing composite rigid (APCR) by the British, high-velocity armor-piercing (HVAP) by the US, and hartkern (hard core) by the Germans. On impact, the core had a much more concentrated effect than plain metal shot of the same weight and size. However, the air resistance and other effects were the same as for the shell of identical size. High-velocity armor-piercing (HVAP) were primarily used by tank destroyers in the US Army and were relatively uncommon as the tungsten core was expensive and prioritized for other applications.
Between 1941 and 1943, the British combined the two techniques in the armour-piercing discarding sabot (APDS) round. The sabot replaced the outer metal shell of the APCR. While in the gun, the shot had a large base area to get maximum acceleration from the propelling charge but once outside, the sabot fell away to reveal a heavy shot with a small cross-sectional area. APDS rounds served as the primary kinetic energy weapon of most tanks during the early-Cold War period, though they suffered the primary drawback of inaccuracy. This was resolved with the introduction of the armour-piercing fin-stabilized discarding sabot (APFSDS) round during the 1970s, which added stabilising fins to the penetrator, greatly increasing accuracy.
The principle of the kinetic energy penetrator is that it uses its kinetic energy, which is a function of its mass and velocity, to force its way through armor. If the armor is defeated, the heat and spalling (particle spray) generated by the penetrator going through the armor, and the pressure wave that develops, ideally destroys the target.
The modern kinetic energy weapon maximizes the stress (kinetic energy divided by impact area) delivered to the target by:
- maximizing the mass – that is, using the densest metals practical, which is one of the reasons depleted uranium or tungsten carbide is often used – and muzzle velocity of the projectile, as kinetic energy scales with the mass m and the square of the velocity v of the projectile
- minimizing the width, since if the projectile does not tumble, it will hit the target face first. As most modern projectiles have circular cross-sectional areas, their impact area will scale with the square of the radius r (the impact area being )
The penetrator length plays a large role in determining the ultimate depth of penetration. Generally, a penetrator is incapable of penetrating deeper than its own length, as the sheer stress of impact and perforation ablates it. This has led to the current designs which resemble a long metal arrow.
For monobloc penetrators made of a single material, a perforation formula devised by Wili Odermatt and W. Lanz can calculate the penetration depth of an APFSDS round.
In 1982, an analytical investigation drawing from concepts of gas dynamics and experiments on target penetration[conflicted source] led to the conclusion on the efficiency of impactors that penetration is deeper using unconventional three-dimensional shapes.
The opposite technique of KE-penetrators uses chemical energy penetrators. There are two types of these shells in use: high-explosive anti-tank (HEAT) and high-explosive squash head (HESH). They have been widely used against armour in the past and still have a role but are less effective against modern composite armour, such as Chobham as used on main battle tanks today. Main battle tanks usually use KE-penetrators, while HEAT is mainly found in missile systems that are shoulder-launched or vehicle-mounted, and HESH is usually favored for fortification demolition.
- ^Shorter Oxford English Dictionary (2007) 6th Ed. p. 2641
- ^"Tank - Armament". Encyclopedia Britannica. Retrieved 2020-02-22.
- ^"Heat Rounds and Sabots". xbradtc.wordpress.com. Archived from the original on 2011-07-18.
- ^M829A3 penetration test, retrieved 2020-02-22
- ^"Long Rod Penetrators. Perforation Equation". www.longrods.ch. Retrieved 2020-02-22.
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Differing By Just 1mm The US 76mm Guns Were So More Effective Than The 75mm Guns
The cannon on a tank is vital in any battle particularly when there are other tanks on the battlefield. According to tank destroyer doctrine, only other tanks should be used to engage with tanks. This increases the need for guns that can destroy enemy tanks from a greater distance.
For years, the Sherman tanks of the US Army were equipped with 75mm guns. These guns were relatively effective during WWII and were able to kill a German tank at 893 yards. They could take on any other tank that they encountered for most of the war.
However, in early 1944, Sherman tanks equipped with 76mm cannons arrived in the UK for testing. By late 1944 to early 1945, these tanks would be deployed in greater numbers. As the guns differed by 1mm only, many people wonder what it was that made the 76mm cannon more viable.
The primary reason why the 76mm was seen as better was its armor penetrating power. This gun is able to penetrate one inch more than its predecessor. This was important because of the new tanks which the Allies encountered toward the end of the war.
The Panzer IV and Panzer IIIs which were encountered in North Africa could fall to the 75mm gun. It was the front armor of the Tiger I that first started to cause problems for the Allies. The 75mm cannons could not penetrate this armor, though they were still able to knock out these tanks from the rear and sides.
When using high-velocity armor-piercing (HVAP) rounds, the 75mm guns were able to penetrate 4 to 4.5 inches of armor at nearly 1,100 yards. The same rounds used in the 76mm gun could penetrate 6 to 7 inches of armor. This was enough to take on the front armor of the Tiger tanks.
The 76mm gun was also able to fire shells at a higher velocity. The 75mm is often cited as barely being a cannon and closer to a howitzer in terms of barrel length. The shorter barrel lowered the overall velocity which made the shells less effective against hard targets like other tanks.
This shorter barrel was fine by commanders who saw the 75mm tanks as being infantry support vehicles, but this was not a vision shared by enemy fighters who often specifically targeted the Shermans with their tanks. The longer barrel of the 76mm cannon allowed the Allies to engage better with those enemy tanks.
The longer barrel of the 76mm cannon also provided the shells with a more powerful charge. The turret was able to handle HVAP ammo which was more effective than high explosive (HE) shells against heavy armor. The HE shells which were used by the 76mm cannon only had a larger exterior with no other differences.
The use of HVAP ammo eventually became a drawback during WWII. These shells had tungsten surrounded by a lighter aluminum. These materials became hard to find close to the end of the war leaving the shells in short supply.
As for HE shells, the explosive power of the 76mm HE shells was not as powerful as those of the 75mm. The 76mm shell had a charge of 0.86lbs while the 75mm had a charge of 1.47lbs. This made the 76mm less satisfactory for medium range tanks, which is how the Shermans were being used at the time.
This reduction in the charge was caused by the necessity for thicker shell walls. The thicker walls allowed the HE shells to be fired from high-velocity guns like the 76mm, but reduced the charge that could be housed.
The 76mm also has a heavy muzzle blast. This impacts the rate of fire as the muzzle dust cloud can take 8 to 30 seconds to clear. In combat, this time was seen as too detrimental by the tank commanders and gunners.
Read another story from us: Panzer Hunters – Soviet Anti-tank Guns of WWII with Photos
As a result of the drawbacks, during the war many tank commanders and crew continued to view the 75mm as being the better option of the two cannons. The replacement of a 75mm cannon for the 76mm one was not an easy process as the entire cannon turret would need to be replaced. The true viability of the 76mm cannon would only develop after WWII.
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