90 mm Gun M1 / M2 / M3 The American 90 mm gun served as a primary heavy anti - aircraft and anti - tank gun , playing a role similar to the renowned German 88 mm gun . It was the US ' s primary anti - aircraft gun from just prior to the opening of World War II into the 1950s , when most anti - aircraft artillery was replaced by guided missile systems . 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 tanks . History . Prior to World War II , the primary US anti - aircraft gun was the 3 - inch M1918 gun ( 76 . 2 mm L / 50 ) , a widely - used caliber for this class of weapon . 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 the decade . However the US Army became interested in a much more capable weapon instead , and on June 9 , 1938 it issued a development contract calling for two new guns , one of 90 mm which it felt was the largest possible size that was still capable of being manually loaded at high elevations , and another , using assisted loading , of 120 mm caliber . The new design seemed so much better than developments of the older 3 - inch that work on the 3 - inch T9 was canceled in 1938 just as it became production - ready . By 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 the standard on May 22 , 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 their standard anti - aircraft gun for the rest of the conflict . Production rates continued to improve , topping out in the low thousands per month . Like the German 88 , and the British QF 3 . 7 inch AA gun , the M1A1 found itself facing tanks in combat , but unlike the others it could not be depressed to fire against them . On September 11 , 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 yet another 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 May 13 , 1943 . Anti - aircraft operation . In anti - aircraft use the guns were normally operated in groups of four , controlled by the M7 or M9 Director or Kerrison Predictor s . 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 dramatically upgraded with the addition of the SCR - 584 microwave radar , which was accurate to about 0 . 06 degrees ( 1 mil ) and provided automatic tracking as well . 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 . With the SCR - 584 the 90 mm became arguably the best anti - aircraft weapon of the war . Anti - tank developments . 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 gun was used on the M36 tank destroyer , and the M26 Pershing tank . A number of experimental versions were developed on the basic M3 pattern , including the T14 which included a standard muzzle brake , the T15 series with an improved muzzle velocity of about per second , the even higher velocity T18 and the T19 , which was an attempt to reduce barrel wear . The T21 , which was intended for wheeled vehicles , and the T22 , which used the breech from the standard 105 mm M2 howitzer to take larger charge cartridges . None of these versions entered service . In the post - war era development of the T15 continued as the T54 , which included the ability to fire tungsten - cored shells at much higher velocities . The T54 was the main armament of the M47 and M48 Patton tanks , and the M56 Scorpion anti - tank vehicle . Variants . M1A1 . Towed anti - aircraft gun . Production began in 1940 . It featured the M8A1 spring rammer . Its rate of fire was 20 rounds per minute . M2 . A complete redesign to make the gun dual role , functioning as an anti - tank gun as well as an anti - aircraft gun . The ammunition feed was upgraded and an automatic fuze setter / rammer , the M20 , was added . This enabled the rate of fire to reach up to 24 rounds per minute . Elevation was improved with the gun able to depress to −10 degrees . To protect the crew , a large metal shield was added . The M2 was the standard weapon by May 13 , 1943 . From the march it could fire from its wheels in three minutes , and from a fully emplaced position in seven minutes . In 1944 the weapon was enhanced with the addition of proximity fuse d shells . M3 . An anti - tank version of the gun . It was used to equip the M36 tank destroyer and the M26 Pershing tank . It is also known as the 90 mm L / 53 .