 For armament, it had a trainable nose-mounted searchlight, a 1½-pounder (37 mm) Davis gun mounted above the top wing with 20 shells, and two .303 in (7.7 mm) Lewis guns.Power for the searchlight was provided by an independent petrol engine-driven generator set made by ABC Motors, possibly the first instance of a recognisable airborne auxiliary power unit.Although touted as being able to reach , the P.B.31E prototype only managed at and took an hour to climb to , which was totally inadequate for intercepting Zeppelins.