Hall-Scott A-7-A, In-line 4 Engine, Cutaway, ca. World War I. Creator: Hall-Scott.

The Hall-Scott Motor Car Company, with general offices in San Francisco and factories at Berkeley, California, began specializing in the construction of airplane engines in 1911. The water-cooled 30 kW (40 hp) Type A-1 was the first aircraft engine produced by the company. This was followed the 45 kW (60 shp) Model A-2 and the 60 kW (80 shp) Model A-3, both water-cooled V-8 engines. The Hall-Scott Model A-7-A primarily powered the World War I Standard Aero Corporation Standard J aircraft. The Standard J and its Hall-Scott A-7-A engine along with the Curtiss JN-4D with its OX-5 engine were the two primary trainer aircraft and engines built in the U.S. during World War I. Despite vibration common to four-cylinder engines at the time, the A-7-A was otherwise regarded by experts as a rugged and dependable motor. The A-7-A also powered other Standard, Aero Marine, and Dayton-Wright aircraft.