In its original configuration, HM595 featured a tail unit and cockpit enclosure similar to those found on the contemporary Typhoon aircraft. Approximately two months after its initial flight, a dorsal fin fairing was added, and the tailplane chord was increased. These modifications were implemented to compensate for the lengthened fuselage and were subsequently incorporated into all production Tempest aircraft. During its testing phase at the Aeroplane and Armament Experimental Establishment (A&AEE), HM595 still retained its original Typhoon-style canopy and featured a larger tailplane along with an interim fin extension for handling trials.