The M16 Multiple Gun Motor Carriage was armed with four .50in anti-aircraft machine guns in a Maxson turret carried on a M3 half-track and replaced the twin-gun M13 in production.
The M13 had been accepted for production in July 1942 after a development process that had begun in October 1940 with the T1 Multiple Gun Motor Carriage. The Maxson turret was mounted in the back of the fighting compartment, which retained its sides (the top part of the sides and back could be folded down to allow the gun to fire at low elevations without a very high mount). The turret itself was carried on a powered turntable, with the gunner sitting in the centre. One .50in gun was carried to each side of the gunner.
A total 1,103 M13s were built, and some saw combat in Italy during 1943, but it was soon realised that it lacked firepower. Work began on a new T61 four-gun version of the Maxson turret, and in November 1942 this was accepted for production as the M45 mount. The new mount was very similar to the two-gun version, but with two .50in machine guns on each side of the gunner. The second gun was mounted below and behind the upper gun in order to make space for a second ammo drum on each side.
The new mount was tested on the M3 half-track with the designation T58, and then accepted for production as the M16 Multiple Gun Motor Carriage. Production of the M16 began in May 1943. It was followed by the M17 MGMC, which combined the M45 mount with the M5 half-track and replaced the earlier M14 MGMC. Production of the M17 began in December 1943.
The M16 MGMC was produced in greater numbers than of the other self-propelled guns on half-tracks. A total of 2,877 were built in 1943-44, 2,323 in 1943 and 554 in 1944. This figure may include the 568 M13s that were upgraded to the M16 standard before being issued to the US Army and the 109 T10 MGMCs that had their 20mm guns removed and replaced with the standard M16 mount in December 1944, but doesn't include those M16s that were produced in the field by mounting towed M45 turrets on standard half-tracks.
The M16 was normally used alongside the M15 Combination Gun Motor Carriage. They served with the anti-aircraft artillery weapons companies of US Armoured Divisions, which were equipped with eight of each type. They were also used in anti-aircraft weapons battalions at corps and army level, equipped with thirty-two of each type. These battalions were used to defend high value locations such as headquarters, bridges or rail junctions.
By the time the M16 entered combat the Luftwaffe was almost a spent force and the M16 was normally used as a ground support weapon. It was very effective in this role and earned the rather gruesome nickname of 'meat-chopper'.
The M16 entered combat in Italy early in 1944. By April 1944 some had reached the Anzio beachhead, where for once they were used as anti-aircraft weapons to help repel heavy Luftwaffe attacks on the beachhead.
The M16 saw most use in the campaign in north-western Europe, fighting from D-Day to the final German surrender. The plans for D-Day had assumed that the Luftwaffe would throw everything it had at the beachhead, but this threat never really developed and by July the M16 was already mainly used as an infantry support weapon.
There was more Luftwaffe activity as the Allies approached the German border late in 1944, but during the battle of the Bulge the M16 was once again used as an infantry support weapon. The M16 did see use as an anti-aircraft weapon early in 1945. On 1 January 1945 the Germans launched Operation 'Bodenplatte', a massed attack on Allied airfields in the Low Countries and France. This was a disaster for the Luftwaffe, which lost irreplaceable pilots in an attack that had no impact on the outcome of the war. The second and final major use of the M16 as an anti-aircraft weapon came in March 1945 after US troops captured the Ludendorff Bridge at Remagen. The Luftwaffe made a series of attacks on the bridge, and a number of M16s took part in the determined American defence of the area.
The M16 was also used by the Polish 1st Armoured Division during the campaign in France in 1944, appearing in British colours.
The M16 saw limited use in the Pacific, but it did fight on Luzon during 1945, where it was used by the 209th Anti-Aircraft Artillery Battalion.
The M16 was one of the few half-track weapons to remain in use after the war, remaining in use into 1950s and seeing combat in Korea. In 1947 most variants on the M3 were declared obsolete, and many surplus M3s were converted into anti-aircraft weapons as the M16A1. The standard M3 lacked the folding sides of the M16, and so on the M16A1 the turret was mounted on a higher pedestal. Some M16A1s was also given 'bat-wing' armoured shields which extended past the sides of the turret to provide protection for the loaders.
The M16 was used extensively during the Korean War, normally as a ground support weapon. It was very effective against Chinese massed infantry attacks. After the Korean War the M16 was replaced in Army service by the M42 Duster twin 40mm gun vehicle, but it remained in use with the National Guard into the 1960s and some were deployed during the 1967 Newark Riots.
Only a handful of M16s were exported during the Second World War. The Free French received the most, getting 70, while only two went to the UK. After the war they were exported in large numbers, and were often given to America's allies, where some remained in use for many years.