Curtiss CW-23

In April 1939, Curtiss-Wright's St Louis Airplane Division flew the prototype of the CW-23 basic combat trainer which was essentially a tandem two-seat, lower-powered derivative of the CW-21 single-seat fighter. It introduced inward-retracting, fully-enclosed main undercarriage members and hydraulically-actuated rather than manually-operated flaps, and these features were adopted for a new version of the single-seat fighter, the CW-21B.
It had a 447kW Pratt & Whitney R-1340 Wasp engine and was intended as a basic combat trainer for the US Army. Flown in 1939, official testing led to its rejection for production.