The 90 mm gun M1/M2/M3 was an American heavy anti-aircraft and anti-tank gun, playing a role similar to the German 8.8cm Flak 18. It had a diameter bore, and a 50 caliber barrel, giving it a length of . It was capable of firing a shell horizontally, or a maximum altitude of .
The 90 mm gun was the US Army's primary heavy anti-aircraft gun from just prior to the opening of World War II into 1946, complemented by small numbers of the much larger 120 mm M1 gun. Both were widely deployed in the United States postwar as the Cold War presented a perceived threat from Soviet bombers. The anti-aircraft guns were phased out in the middle 1950s as their role was taken over by surface-to-air missiles such as the MIM-3 Nike Ajax.
As a tank gun it was the main weapon of the M36 tank destroyer and M26 Pershing tank, as well as a number of post-war vehicles like the M56 Scorpion. It was also briefly deployed from 1943–1946 as a coast defense weapon with the United States Army Coast Artillery Corps. Each gun cost roughly $50,000 to make in 1940 and utilized up to 30 separate contractors to manufacture.The Ordnance Department: Procurement and Supply
History Prior to World War II, the primary US anti-aircraft guns were the 3-inch M1918 gun (76.2 mm L/40) and its modernized successor, the 3-inch anti-aircraft gun M3 (76.2 mm L/50); 3 inches or 76.2 mm was a widely used caliber for this class of weapon at the time, and similar weapons were in British, Soviet and other arsenals. There had been several upgrades to the weapon over its history, including the experimental T8 and T9 versions developed in the early 1930s, that were intended to enter service later in that decade.
However, the US Army became interested in a much more capable weapon instead, and on 9 June 1938, it issued a development contract calling for two new guns, one of 90 mm caliber, which it felt had the largest possible projectiles that were capable of being manually loaded when the gun was at high elevations, and another (using mechanically assisted loading) of caliber. On 18 August 1938 the development of the Mount T1 was approved as well. The new design seemed so much better than developments of the older three-inch that work on the three-inch T9 was canceled in 1938, just as it became production-ready. On 21 March 1940, the second development of the 90 mm design, the T2, was standardized as the 90 mm M1, while its larger cousin became the 120 mm M1 gun.
A few hundred M1s were completed when several improvements were added to produce the 90 mm M1A1, which entered production in late 1940, and was accepted as standard on 22 May 1941. Since national arsenals had limited capacity, production of the first 300 gun mounts was contracted to Allis-Chalmers in November 1940, with the first unit shipped to the Army in September 1941. The M1A1 included an improved mount and spring-rammer on the breech, with the result that firing rates went up to 20 rounds per minute. Several thousand were available when the US entered the war, and the M1A1 was the standard anti-aircraft gun for the rest of the conflict. Production rates continued to improve, topping out in a few thousand per month. Year 1941 1942 1943 1944 1945 TotalProduction 171 3286 4074 300 0 7831 Like the German 8.8 cm Flak 18/36/37/41 and the British QF 3.7 inch AA gun, the M1A1 was used against tanks in combat but, unlike the others, the original mount design could not be depressed low enough to allow fire against them. On 11 September 1942, the Army issued specifications for a new mount to allow it to be used in this role, which resulted in the 90 mm M2, introducing a new mount that could be depressed to 10 degrees below the horizontal and featured a new electrically assisted rammer. It became the standard weapon from 13 May 1943.
Anti-aircraft operation
In anti-aircraft use, the guns were normally operated in groups of four, controlled by the M7 or M9 gun director or Kerrison predictors. Radar direction was common, starting with the SCR-268 in 1941, which was not accurate enough to directly lay the guns, but provided accurate ranging throughout the engagement. For night-time use, a searchlight was slaved to the radar with a beam width set so that the target would be somewhere in the beam when it was turned on, at which point the engagement continued as in the day. In 1944, the system was upgraded with the addition of the SCR-584 microwave radar, which was accurate to about 0.06 degrees (1 mil) and also provided automatic tracking. With the SCR-584, direction and range information was sent directly to the Bell Labs M3 gun data computer, and M9 director, which could direct and lay the guns automatically, all the crews had to do was load the guns.
Main anti-tank developments
90 mm gun M3 The M3 was also adapted as the main gun for various armored vehicles, starting with the experimental T7 which was accepted as the 90 mm M3. The test firing of the M3 took place on an M10 tank destroyer in early 1943. The M3 gun was used on the M36 tank destroyer, and the T26 (later, M26) Pershing tank.Green, Michael, Tiger Tanks At War, Zenith Press, , 076033112X (2008), pp. 118-122 The M3 fired an M82 APC shot with a muzzle velocity of . However, both the muzzle velocity of the standard M3 gun and the quality of the steel used in the M82 APC (armor-piercing capped) shot, while comparable to the 8.8 cm KwK 36 L/56 mounted on the Tiger I, were inferior to the Tiger II's KwK 43 L/71 8.8 cm main gun firing its standard APCBC (armor-piercing capped ballistic cap) shot used by German forces, with the result that the former's penetration fell far short of the standard projectile fired by that German tank. As a result, US ordnance provided some T26/M26 tank crews with the 90 mm HVAP (high-velocity, armor-piercing) tungsten penetrator sub-caliber projectile with a muzzle velocity of , or the T33 AP with a re-heat-treated projectile with ballistic windshield and a muzzle velocity of .Armor-Piercing Ammunition for Gun, 90-mm, M3, Washington, D.C., U.S. Army: Office of the Chief of Ordnance (January 1945) The HVAP could compete with the KwK 43's penetration performance when firing standard APCBC, but tungsten ammunition was always in short supply.
Ammunition (M3 gun) M71 HE – (projectile) M77 AP – (projectile) M82 APC – (projectile)
Performance (M3 gun) +Calculated penetration at range (90 degrees) using 50% success criteria. Muzzlevelocity(m/s) Penetration (mm) 100 m 250 m 500 m 750 m 1,000 m 1,250 m 1,500 m 1,750 m 2,000 m 2,500 m 3,000 mM77 APversus FHA 168 159 146 134 122 112 102 94 86 72 60M77 APversus RHA 188 179 163 150 137 125 115 105 96 81 68M82 APCversus FHA 151 150 147 144 140 135 131 127 123 115 107M82 APCversus RHA 164 156 150 143 137 131 125 119 114 104 92Late M82 APCversus RHA 169 168 164 157 151 144 140 136 132 123 116Late M82 APCversus FHA 161 159 155 151 147 144 138 133 127 115 104T33 APversus RHA 206 201 193 185 178 170 164 157 150 139 128T30E16 HVAP 306 295 278 262 246 232 218 205 193 171 151
90 mm gun T8
An unsuccessful anti-tank variant was the T8 gun on the T5 carriage. The gun was an M1 with the recoil mechanism from the M2A1 105 mm howitzer. The combination of the 90mm gun and the T5 carriage was very long, so the trails of the carriage could be folded back to reduce their length, while the gun could rotate by 180 degrees so the barrel was facing back over the trails when being towed. However trials in January 1944 showed that this design didn’t work. A more conventional carriage T5E1 was designed, but this failed trials in June 1944. Finally the T5E2 passed its trials, ready to be used on a batch of 600 guns that had been ordered.
An alternative AT gun to the T8 was developed, the 90mm T9 gun, which had an unorthodox carriage in which the shield formed the basic member and the trail legs were hinged to the top corners; the legs stretched rearwards for firing and could be folded forward to lie alongside the barrel for towing. This design was worked on through 1944 and 1945 but without reaching a serviceable result.
The 90mm T8 gun on T5E2 carriage was classified as limited standard on 7 September 1944. The first three T8s were completed in 1944 and the entire rune of 200 by June 1945. Only one actually reached Europe during the war, with the Zebra mission, which took a number of experimental weapons to the front (including the T26E3 Pershing). However by this point towed anti-tank guns had been discredited and there is no record that the T8 ever saw any combat.
After the war the 90mm gun was used by the anti-tank batteries of the Airborne Divisions, even though they were too large to be carried in any of the available aircraft. They were removed from service in the early 1950s.
An improved version of the T8 was produced, the T25 gun, which had a muzzle brake. But this seemed to be an experimental prototype.
Eventually a version of the T8 with the T20E1 gun and T15 carriage was tested; this led to the 105 mm anti-tank gun T8.
90 mm gun T15 Because the standard fifteen-and-a-half foot long M3 90 mm main tank gun proved incapable of penetrating the heaviest frontal armor of the heaviest German tanks such as the Tiger II tank and the rarer Jagdtiger tank destroyer variant, a number of improved versions of the M3 were developed, including the T14 which included a standard muzzle brake and the T15 series. The 90 mm T15E1 L/73, with its long barrel, was designed and developed as an AT gun that could match or surpass the performance of the 8.8 cm KwK43 L/71 cannon, the famous long 88 on the Tiger II.
Two versions of the T15 were made: the T15E1 with single-piece ammunition and the T15E2 with two-piece ammunition.
By mid-March 1945, a T26E1 pilot was equipped with the 90 mm T15E1 and was sent to Europe in a ''trial by combat''. It was given to the 3rd Armor Division where it was enhanced with additional armor plates. Its gun was fired in anger on only one occasion, on 4 April 1945, where it engaged and destroyed a German armored vehicle, probably a Tiger I or Panther, at a range of during the fighting along the Weser River. According to the memoirs of John P. Irwin, it knocked out a King Tiger in Dessau as well as a Panzer IV and a Panther. However, the Tiger II claim is disputed by historians on the grounds that the nearest unit known to be equipped with Tiger IIs was 70 miles from Dessau on the date when the kill was claimed.
Near the end of World War II, more experimental versions of the 90 mm gun were tested including the higher-velocity T18 and T19 main guns. The T19 was a T18 modified in an attempt to reduce barrel wear. Other versions included the T21, which was intended for wheeled vehicles, and the T22, which used the breech from the standard 105 mm M2 howitzer. The T21 and T22 were designed to use larger powder charges. None of these versions entered service.
In the post-World War II era, development of the T15 continued redesignated as the T54, which used a slightly shorter and fatter propellent casing than that of the T15E1.Hunnicutt, R.P. Pershing: A History Of The Medium Tank T20 Series, Presidio Press, , 9780891416937 (1999) The T54 served as the main gun on the M26E1 Pershing.
Ammunition
The T15 90 mm L/73 anti-tank gun utilized many types of armor piercing ammunition.
T43 APBC: A solid shot, it was a modified T33 for use by the T15. It had a muzzle velocity of and therefore increased penetration capabilities. It could punch through of armor angled at 60°(from vertical) up to about . T41 APCBC: Modified M82 projectile of the M3 cannon, fired at a much higher velocity of 3,200 ft/s, than the normal 2,670 ft/s. It could defeat up to of vertical armor at . T44 HVAP: Modified M304(T30E16) for use out of the T15. Muzzle velocity of . Maximum penetration of of vertical armor at 30 ft.