The first variant of the P.11 to be ordered by the Polish Air Force was the P.11a. From the onset, this was considered to be only an interim model of the type; accordingly, a series of 50 such fighters were constructed. Otherwise similar to the P.7, the P.11a mounted the 575 hp (429 kW) Bristol Mercury IV S2 radial engine, which was produced in Poland under licence. Upon the completion of the P.11a order, PZL immediately set about establishing the production of an improved model of the aircraft, which was designated as the P.11c.