90 mm Gun M1/M2/M3

In 1949, the Delaware Army Guard was authorized to expand to brigade strength. Units consisted
of the 261st Anti-Aircraft Artillery Brigade, the 160th Anti-Aircraft Artillery Group, the 156th
expanded from the 736th and a new 945th (later the 280th) was a reorganization of the pre-war
261st Coast Artillery. The former 945th in Kent County (the old second battalion of the 198th
Coast Artillery) was redesignated the 193rd Anti-Aircraft Artillery Battalion.

The reorganization was hardly underway when in June 1950 North Korea moved south across
the 38th Parallel and the United States was at war again - though "police action" was the favored
term. The 736th Anti-Aircraft Artillery Battalion was at
summer camp when word came of its
order into federal service, along with several other small detachments. About one-third of the
Army National Guard, both in Delaware and nationwide, went on active duty.

The 736th served first at Fort Stewart, Georgia, then moved to Fort Meade, Maryland, where with
90mm guns, it became one of the first units in the newly-established Air Defense of Baltimore
and Washington. By the time the unit was returned to the State in 1952, few of its original
members were still with it. Most had been transferred out and many saw combat service in Korea
with other units under the policy of individual replacement then in effect.

Throughout the Cold War much reorganization, expansion and consolidation occurred in Guard
units, especially in Delaware. Initially, two new anti-aircraft battalions, the 197th in Smyrna and
the 945th in Laurel, were formed in the mid 1950s to meet these new challenges. In addition, two
of Delaware's six battalions received the new self-propelled twin-40mm "Dusters," and two other
battalions received the 75mm "Skysweeper" guns. At this time the 116th Mobile Army Surgical
Hospital was organized in Wilmington.

90 mm M1A1

Type        Anti-Aircraft gun
Place of origin         United States
Service history In service        1940 -
Used by         United States  Canada
Wars        Second World War
Weight        8.618 metric tons
Barrel length        53 calibers
Shell        90×600 mm. R
Caliber        90 mm.
Carriage        mobile
Rate of fire        20 rpm
Muzzle velocity        823 m/s
Effective range        Maximum horizontal 17,823 m
Maximum slant
Ceiling 10,380 m

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 and Heavy Tank M26 Pershing, as well as a number of post-war tanks.


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 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 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 3.7 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
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 M9 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 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 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, 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.


Towed anti-aircraft gun. Approved for service in 1940.
Fixed on M3 mount for Coast Artillery
Towed anti-aircraft gun. Production began in 1940. Featured the M8A1 spring rammer. Rate of fire
20 rounds per minute.
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.
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 lb)
Barrel weight: 1,109 kg (2,445 lb)
Length with the carriage: 4.73 m (15.5 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.

Surviving examples

one AAA at CFB Borden, Ontario, Canada
one AAA at Sangudo Alberta [1]
one AAA at Whycocomagh, Nova Scotia [2]
three at Pre-Fair army surplus sales, at Belœil, near Montreal, Quebec, Canada
one AAA at Fort Rodd Hill - Colwood, BC [3]
one at Savannah, Georgia: National Guard Fairgrounds
one at Arundel, Quebec, Canada: Legion Hall
one AAA at Sault Ste Marie Ontario [4]
one on barbette carriage at Shemya, Alaska. [5]
one AAA at U.S. Army Ordnance Museum. [6]
one AAA at Broadalbin, New York [7]
one AAA at Roswell, New Mexico [8]
one AAA at Greenville, South Carolina [9]
one AAA at Anderson, South Carolina VFW post
Delaware Military History