90 mm gun

Infobox Weapon|is_artillery=yes


caption= 90 mm M1 at CFB Borden
name= 90 mm M1A1
origin= Flag|United States
era=WW II
target=aircraft
type= Anti-Aircraft gun
date= 1940
prod_date=1940 -
service=1940 -
used_by=Flag|United States
wars=Second World War
carriage=mobile
caliber=90 mm
part_length= 53 calibers
breech=
rate= 20 rpm
velocity= 823 m/s
cartridge= HE
ammo_wt= 10.61 kg
range=Maximum horizontal 17,823 m
Maximum slant
Ceiling 10,380 m
recoil=
weight= 8.618 tonnes
length=
crew=
number=

The American 90 mm family of guns served as primary heavy anti-aircraft and anti-tank guns, playing a role similar to the renowned German 88 mm gun. They were the US's primary anti-aircraft guns from just prior to the opening of World War II into the 1950s when most AAA was replaced by missile systems. As a tank gun, it was the weapon featured on the 90mm Gun Motor Carriage M36 (Jackson) and Heavy Tank M26 Pershing, as well as a number of post-war tanks.

History

Prior to WWII, the primary US anti-aircraft gun was the 3-inch M1918 gun (76.2 mm L/50), a widely-used caliber for this sort 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 Army became interested in a much more capable weapon instead, and on June 9, 1938 they issued a development contract calling for two new guns, one of 90 mm which they 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 M1's 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 breach with the result that firing rates went up to 20 rounds per minute. Several thousand were available when the US entered in the war, and the M1A1 was their standard AA gun for the rest of the war. Production rates continued to improve, topping out in the low thousands per month.

Like the German 88, and the British QF 3.75 inch AA, 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 horizontal and featured a new electrically-assisted rammer. It became the standard weapon from May 13, 1943.

AA operation

In AA use the guns were normally operated in groups of four, directed by the M7 or M5 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 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 M9 predictor, which could direct and lay the guns automatically. All the operators 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 a 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 3in Gun Motor Carriage M10 in early 1943. The gun was used on the 90mm Gun Motor Carriage M36 tank destroyer, and the Heavy Tank M26 Pershing.

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 975 meters per second, the even higher velocity T18, the T19 which was an attempt to reduce barrel wear, the T21 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

M1

Towed anti-aircraft gun. Approved for service in 1940.

M1A1

Towed anti-aircraft gun. Production began in 1940. Featured the M8A1 spring rammer. Rate of fire 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 3 minutes, and from a fully emplaced position in 7 minutes. In 1944 the weapon was enhanced with the addition of proximity fused shells.

M3

An anti-tank version of the gun. It was used to equip the 90mm Gun Motor Carriage M36 and Heavy Tank M26 Pershing. It is also known as 90 mm L/53.

General characteristics (M1A1)

* Caliber: 90 mm L/53
* Total weight: 8,618 kg (18,999 lbs)
* Barrel weight: 1,109 kg (2,445 lbs)
* Length with the carriage: 4.73 m (5.5 ft)
* Length: 4.60 m (15 ft)
* Width: 4.16 m (13.64 ft)
* Height: 3.07 m (10 ft)
* Weight of the projectile: 10.61 kg (23.39 lb)
* Rate of fire: 25 rounds per minute (at most)
* Muzzle velocity: 823 m/s (2,700 ft/s)
* Range: 17,823 m (20,585 yd)
* Ceiling: 10,380 m (34,050 ft) (limited by 30 second fuse)
* Elevation : +80 to −5 degrees
* Traverse : 360 degrees.

External links

* [http://www.lemaire.happyhost.org/armes/artillerie/5402.html LemaireSoft encyclopedia]
* [http://gva.freeweb.hu/weapons/usa_guns7.html M3 armor penetration table]