I photographed this M6 37mm Gun Motor Carriage at the National Museum of Military Vehicles in Dubois WY
These were mounted on the Dodge WC51 Cargo Truck. It had success against the light Japanese tanks through 1944 — but after limited effectiveness against the heavier German tanks in Europe, most were stripped of the guns and converted back to Cargo Trucks. The M6 was replaced by the M3 Gun Motor Carriage and the M10 Tank Destroyer