Replacing the aging 3-inch gun as the staple of Army heavy antiaircraft artillery at the dawn of the war, the 90mm gun went on to earn a well deserved place among the finest artillery pieces fielded by the Allies in World War II. Intended to meet the threat posed by aircraft capable of flying faster and higher, work on the 90mm began in earnest in 1938. The 90mm gun M1 was standardized in March 1940. An M1A1 version followed that added a small loading tray to the breech ring and included accommodations for a spring rammer to facilitate faster reloading. The updated M2 version of the ninety was standardized in May 1943 and sported a redesigned breech that mounted a fully automatic fuze setter-rammer. This improvement increased the 90mm gun's rate of fire to an impressive 23 to 28 round per minute.
The initial M1 mount for the ninety was a traditional "spider" design with a detachable platform and one single-axle, dual-wheeled bogie (four wheels total). In May 1941, the M1A1 replaced the original model as the standard mount for the ninety. The M1A1 mount was essentially the same as the M1 version, but introduced remote control capabilities that allowed the gun to be aimed by the battery's director through new electric-hydraulic mechanisms.
Field evaluations of the M1A1 mounts spurred development of the enhanced M2 mount, standardized in May 1943. The M2 was intended to increase the 90mm gun's capabilities in its secondary role against ground targets. The redesigned M2 featured single-axel front and rear two-tire bogies, folding platforms and armor shielding for the gun crew. Unlike the earlier mounts, it was not necessary to fully emplace the M2 before firing, enabling the 90mm gun to engage both air and ground targets more quickly. The M2 mount also depressed to a -10?, allowing the ninety to wrestle with ground troops, armored vehicles and various water craft when necessary. Early test versions of the M2 mount, notable the T2E1, made it to the field mounting M1 or M1A1 guns while development of the rammer for the 90mm M2 gun was completed.
Additionally, there was a fixed-mount M3 pedestal designed for the M1 gun. This heavily armored mount was designed primarily to convert the ninety into an effective anti-motor torpedo boat weapon, although the M3 mount was also able to fully elevate to +80? and engage aircraft by manual or remote control. After all, the 90mm was still first and foremost an antiaircraft gun. All 90mm mounts incorporated a direct fire sighting system for use against ground targets or watercraft. 90mm antiaircraft guns
90mm Antiaircraft Gun Facts
Firing Table Muzzle Velocity: 2,700 feet/second
Maximum Rate of Fire: 15 to 25 rounds/minute
Elevation Limits: 0? to 80? (down to -10? on the M2 mounts)
Recoil Type: Hydro-pneumatic
Fire Control Director: M7 or M9
Maximum Effective Slant Range: 11,500 yards
Maximum Effective Horizontal Range: 12,600 yards
Maximum Effective Vertical Range: 11,000 yards
Maximum Effective Fire Control Altitude: 30,000 feet
Actual muzzle velocity was dependent on ammunition used and environmental conditions. Maximum range was limited by a 30-second timed fuze.