Although not nearly as well known as the quad mount halftracks, the Antiaircraft Artillery did employ tracked motor carriages armed with the .50 caliber twin mount M33 turret.  These halftracks were an intermediate step in the evolution of self-propelled antiaircraft machine gun carriages. 

     The Army well understood the necessity of mobile antiaircraft protection against low-level air attacks on marching columns.  Interwar and early World War II mobile implementations involved mounting single water-cooled  machine guns on a variety of vehicles from small trucks to M2 halftracks.  With the development of the M33 twin gun power mount, the use of single fifties became somewhat archaic.  An initial experiment wed the M33 mount to a 6X6 truck, but the combination of the twin turret on White's M3 Personnel Carrier halftrack quickly rose as the obviously better option.  This combination was dubbed the Multiple Gun Motor Carriage M13 and was standardized in September 1942.  A substitute version, using the M5 halftrack manufactured by International Harvester as a carriage, was designated the M14.  The M13 and M14 are difficult to distinguish, being very similar in external appearance.  Both models incorporated hinged armor side and rear panels that folded down to allow the machine guns to depress below horizontal.

White's Multiple Gun Motor Carriage M13 (above).  Compare to the photo of the IHC M14 (below). 

     The M13 was but the beginning of a good idea.  If two machine guns were good, four would be better.   Just a few short months after the standardization of the M13/M14, the Antiaircraft Artillery Board would pair the M3 halftrack with the quad mount M45 turret, creating the legendary M16 halftrack, which promised a greater volume of fire.  As the self-propelled quad mount vehicles rolled off production lines, the M13 was relegated to the status of a substitute standard.       

Well camouflaged twin mount antiaircraft halftrack somewhere in Italy. Both machine guns fired simultaneously.

The M33 twin mount turret (shown without shield) could traverse and elevate at a rate of 60° per second. The quad mount M45 turret was very similar, but used another style of switch box due to its different electrical system.		Inside view of the M33 twin mount turret used on the M13 halftracks.  The handles connected to the switch box moved the turret in azimuth and elevation.  The triggers that fired the machine guns were part of the handle assembly.  The Navy Mark IX reflector sight is mounted between the hinged armor panels at the top of the turret.

Good use of camouflage netting and natural vegetation render this M13 track nearly invisible to the enemy. This crew is protecting a river crossing in southern France - a common mission for Antiaircraft Artillery.

SOME PREDECESSORS OF THE ANTIAIRCRAFT HALFTRACK MOTOR CARRIAGES

Prewar mobile antiaircraft protection was simple.  A light 4X4 truck mounting a water-cooled .50 caliber machine gun was thought sufficient.  This photo of a camouflaged truck has the door markings scratched out by an Army censor. The .50 caliber machine gun is on an M2 mount.

Twin fifties on an M33 Maxon turret mounted experimentally on a 6X6 truck at Aberdeen.	Although the Navy loved the 20mm Oerlikon, Army AAA never embraced the weapon.  However,  they were not above trying out twin twenties on a halftrack. This test vehicle's power turret is essentially the same as that used for the .50 caliber machine guns.

The T1E2 test vehicle used an M2 halftrack chassis as the carriage for the M33 twin fifty turret.  This arrangement was next tried on an M3 chassis as the experimental T1E4, which became the M13.

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