The M13 Multiple Gun Motor Carriage was the first in a series of anti-aircraft weapons that saw machine guns mounted on a half-track chassis, and was armed with twin .50in machine guns on the back of a M3 half-track personnel carrier.
The first attempt to produce a self propelled .50in anti-aircraft gun was the T1 of October 1940. This used a Bendix twin .50in aircraft turret, mounted on a jeep and on an early M2 half-track car.
The T1E1 was a modified version of the T1, but the Bendix turret was awkward to install on the half-track, and gave the vehicle a high profile.
In November 1941 work began on two alternative designs using new turrets. The T1E2 used a Maxson M33 turret that had been designed specifically for use on vehicles, and that carried two .50in machine guns. The T1E2 and T1E3 were both built on the M2 half-track car. The T1E2 prototype was later given a quad Maxson turret and redesignated as the T61. This design was later accepted for production as the M16.
The T1E3 was the second design, and was armed with a Martin Aircraft turret designed for use on bomber aircraft. This was also armed with two .50in machine guns, used electro-dynamic controls and had the curved glass cover as the aircraft version.
The Maxson turret performed best in comparative tests using the T1E2 and T1E3, but the M2 half-track was a little cramped, and so the same turret was mounted on the back of an M3 half-track to produce the T1E4.
M13 Multiple Gun Motor Carriage
On 27 July 1942 the T1E4 was accepted for production. It was standardized as the M13 Multiple Gun Motor Carriage. A total of 1,103 M13s were built in 1942-43, with work completed by May 1943.
Of these vehicles 586 were then converted into quad-gun M16 Multiple Gun Motor Carriages before they were delivered to the US Army.
The main feature of the M13 (and the closely related M14, M16 and M17) was the Maxson turret. This was mounted on a turntable which was carried inside the fighting compartment of the half-track. The gunner sat in the middle of the turret, with the guns on either side, an armoured shield in front and an electrical generator and battery behind. Ammo drums were mounted outside the guns, looking somewhat like 'ears'. The gun sights were mounted on a bar above the gunner's position. The electrical generator was used to power the traverse and elevation of the turret, allowing it to be used when the half-track's engine was turned off. The turret could be fully traversed in six seconds, and the guns could elevate from -10 degrees to +90 degrees in under two seconds. The guns could fire 50rpm in sustained fire or quick bursts of 250rpm.
The turret was mounted on a modified M3 half-track personnel carrier. This retained the superstructure sides of the fighting compartment, but gave them a hinged top that could be dropped down. This allowed the gun to be mounted lower in the vehicle, reducing its profile, while also still allowing it to fire at a low elevation.
The M13 was the first in a series of related anti-aircraft weapons that entered production.
The M14 Multiple Gun Motor carriage was the same basic design, but built on the M5 half-track. A large number of M14s went to Britain, where most of them had the guns removed to turn them back into normal half-tracks.
The biggest problem with the M13 was the lack of firepower. Maxson produced a new turret armed with four .50in machine guns, and this replaced the twin-gun turret in production.
The M16 carried the quad turret on the M3 half-track and replaced the M13. It was the main American service version.
The M17 carried the quad turret on the M5 half-track. The entire production run went to the Soviet Union.
The M13 made its combat debut in small numbers during the Italian campaign. Some took part in the Anzio landings in January 1944, where they were used in the anti-aircraft role to help repel the heavy German attacks on the beachhead.
By this point it was already clear that the twin .50in armament of the M13 was inadequate and work had moved on to the quad .50in armed M16 MGMC and M17 MGMC. The M16 entered service with the US Army, and by April 1944 some M16s had been deployed to Anzio. After this the M13 was rapidly phased out.