In 1942, the United States Army Air Forces (USAAF) in Australia issued a requirement for a light armoured car to be used in patrolling and airfield defence.

The requirement resulted in a vehicle designated Scout Car S1 (American).

The open-topped armoured hull was similar to that of the M3 Scout Car.

The armament consisted of one .50 inch (12.7 mm) heavy machine gun and two .30 inch machine guns on skate rails, operated by the crew of five.

[2] As of late 2017, two S1 cars are known to be preserved: one restored at the Australian Armour and Artillery Museum, in Cairns,[3] and another in a private collection.