Looking to improve the design, Lockheed delivered the Vega 5 in 1929. Adding the Pratt & Whitney R-1340 Wasp engine of 450 hp (336 kW) and a new NACA cowling improved performance enough to allow the addition of two more seats, and increased cruising speed to 155 mph (249 km/h) and top speed to 165 mph (266 km/h). The new six-seat configuration proved to be too small, and the 5 was purchased primarily for private aviation and executive transport. A total of 64 Vega 5s were built. In 1931, the United States Army Air Corps bought two Vega 5s; one designated C-12 and one as the C-17. The C-17 had additional fuel tanks in the wings.