But it remained a prototype because a decision was made to use a licence-produced radial engine in the Polish Air Force fighters.

So the next model, the PZL P.6, flown in August 1930, was powered by the Bristol Jupiter VI FH radial engine.

After numerous changes, most noticeably the addition of a wide Townend ring to the engine, and a higher aspect tail, the second prototype P.7/II which had been completed in autumn 1931, was accepted for production with the designation P.7a.

Puławski continued to develop the basic design by adding more powerful engines, which resulted in the PZL P.11.

The two-spar trapezoid wing was thinner by the fuselage and was covered with a ribbed Wibault type duralumin sheet (although the upper surfaces were smooth) and braced by two struts on each side.

The aircraft was powered by a 360 to 390 kW (480 to 520 hp) Bristol Jupiter VII F radial engine fitted with a Townend ring and two-blade propeller.

At the outbreak of World War II on 1 September 1939, the Polish Air Force still had 30 PZL P.7a fighters in combat units.

Their two machine guns was also inadequate and jammed frequently while only some replaced the vintage Vickers with the better PWU FK wz.33 [pl].

[1] Pilots flying the P.7a claimed to have shot down seven German aircraft (two Heinkel He 111s, two Dornier Do 17s, one Henschel Hs 126 and two Messerschmitt Bf 110s), against 22 losses.