Developed as a stop-gap to fill in for delayed P.Z.L. P.50 Jastrzab fighters by strengthening the structure to absorb the power of a single 840 hp P.Z.L. Mercury VIII, with an enclosed cockpit and four improved 7.92 mm (0.312 in) KM Wz 36 machine-guns. The converted P.11c prototype flew for the first time on 15 August 1939, less than a month before the German invasion, forcing abandonment of the programme.