 The XSB3U was modified from the last production SBU Corsair, using essentially the same airframe, including a fully enclosed cockpit, and Pratt & Whitney R-1535 radial engine, but with a more streamlined surface and cowling.In addition, the XSB3U had fully retractable landing gear.The XSB3U-1 was delivered to Naval Air Station Anacostia for evaluation by the U.S. Navy in April 1936;, at the same time as its primary competitor, the XSB2U-1.