04/30/2019. Remarks by Johan Visschedijk: "A progressive development of the P.7 stressed to accept more powerful radial engines, the P.11 stemmed from a decision to adapt the basic fighter for the Bristol Mercury engine. The first of three prototypes, the P.11/I, was fitted with a Jupiter 9Aab because of non-availability of the Mercury and flew in August 1931, the P.11/II and P.11/III following with the Mercury IV engine.

Thirty P.11A fighters powered by the Mercury IV.S2 with a maximum output of 575 hp were purchased for the Polish AF, and fifty similar aircraft powered by the 670 hp Gnome & Rhône 9Krsd Mistral were purchased by Romania as P.11Bs. The P.11C, first flown late in 1933, featured a lower engine thrust line, a modified wing center section and re-positioned pilot's cockpit. The first fifty or so for the Polish AF had the 600 hp Mercury V.S2, and a further 125 had the 645 hp Mercury VI.S2. Armament comprised two 0.312 in (7.92 mm) machine guns, but provision was made for the installation of two similar guns in the wings.

A Romanian license-built version of the P.11C with a 640 hp IAR-K9 engine and four 0.312 in (7.92 mm) FN-Browning guns was designated P.11F, seventy being built by Industria Aeronautica Româna (IAR) during 1936 to 1937. A decision to reinstate the P.11 in production was taken in the spring of 1939, in a version known as the P.11G Kobuz (a small species of falcon) with a PZL-built Mercury VIII engine of 840 hp. A prototype was produced by modifying a P.11C and this was flown on August 15, 1939, but series production had not begun when Poland was overrun by German forces.

Pictured is the sole surviving fighter from the Polish Air Force of 1939, it flew with the 121st Flight of the 2nd Air Regiment in Cracow."