XP-13 Viper

The XP-13 Viper was an experimental fighter developed by Thomas‑Morse Aircraft in the late 1920s, intended to replace aging biplane scouts in the United States Army Air Service. Conceived in 1928, the Viper combined a low‑wing monoplaned layout with a powerful 600 hp Curtiss D-12 liquid‑cooled V‑12 engine, delivering a top speed of 210 mph, unprecedented for a domestic fighter at the time. Its all‑metal fuselage and semi‑monocoque construction marked a shift away from the wood‑and‑fabric structures that dominated World I designs. The aircraft featured fully enclosed cockpit, retractable split‑type landing gear, and an innovative wing‑fold mechanism that facilitated storage on aircraft carriers. Flight testing in 1929 revealed superb maneuverability and a climb rate of 3,500 ft/min, but structural vibration problems and the rapid emergence of more refined designs, such as the Boeing P‑26, led to the cancellation of the production contract after only two prototypes were built. Although the XP‑13 never entered service, its advanced aerodynamic concepts and metal airframe technology directly influenced later U.S. fighter development, cementing Thomas‑Morse’s role in the transition to modern combat aircraft. The XP‑13 remains a celebrated example of bold engineering experimentation.