was especially designed for vertical mounting in helicopters. During the mid-1930s, Pratt & Whitney developed a still greater improvement of the Wasp Junior, the "C series", with an even higher compression ratio and RPM limit. The only type produced in this series, the Wasp Junior SC-G, could sustain at an altitude of and could produce for takeoff. It also included reduction gearing to allow the high-revving engine to drive a propeller at suitable speeds, hence the "-G" suffix. Aviator Jacqueline Cochran flew a special Model D-17W Beechcraft Staggerwing with this engine in 1937, setting a speed and altitude record and placing third in the Bendix transcontinental race. However, the SC-G never got past the experimental stage. Operational history Early versions of the Wasp Junior were used in various small civilian and military utility aircraft, but only in limited numbers. The type became more popular later in the 1930s. It was selected for the Lockheed Model 10A Electra twin-engined airliner, as well as for other small twin-engined civil transports like the Lockheed Model 12A Electra Junior, the Beechcraft Model 18, and the Grumman Goose amphibious aircraft. It was also used in single-engined civilian utility aircraft like the Beechcraft Staggerwing, the Howard DGA-15, and the Spartan Executive. As World War II arrived, the U.S. military chose the Wasp Junior for the Vultee BT-13 Valiant and North American BT-14 basic training aircraft and for the Vought OS2U Kingfisher observation floatplane. Military versions of existing Wasp Junior-powered civilian aircraft were also produced, such as the military derivatives of the Beech 18, Beech Staggerwing, Grumman Goose, and Howard DGA-15. The Wasp Junior also powered some versions of the British Avro Anson and Airspeed Oxford twin-engined trainers. The demands of World War II led to the production of many thousands of Wasp Juniors. Until the end of the war, the Wasp Junior's closest competitor was Wright Aeronautical's R-975 Whirlwind. However, during the war, the Wasp Junior was far more widely used in aircraft than the R-975, and Wright ceased production of the R-975 in 1945. After World War II, many military-surplus aircraft with Wasp Junior engines entered the civilian market. New designs based on the Wasp Junior were also introduced, such as the Sikorsky H-5 helicopter, the de Havilland Canada DHC-2 Beaver, and Max Holste Broussard bush airplanes, and agricultural aircraft such as the Snow S-2B and S-2C, Grumman Ag Cat, and Weatherley 201. Pratt &