I photographed this M15 Combination Gun Mortar Carriage at the Fort Lewis Military Museum. This self-propelled anti-aircraft gun on a halftrack chassis was equipped with one M1 automatic 37mm gun and two water-cooled .50 caliber M2 Browning heavy machine guns. Other WWII halftracks include the M3 Halftrack (Autocar, Diamond T, White Motor Co.) and the M5 Halftrack (International Harvester).