It was in effect a one-third scale glider version of Keith-Lucas' ambitious preliminary design P.D.1,[1][2] intended to meet the Air Ministry's (V bomber) specification B.35/46, which was the basis for the Avro Vulcan, the Handley-Page Victor and the Vickers Valiant.

The torsional instability and tip stalling characteristics of conventional swept wings were recognised at the time, together with their tendency to aileron-reversal and flutter at high speed.

During the second flight of the day (using a longer towline intended to alleviate the turbulence), the test pilot encountered severe buffeting problems and he had to cast off at low altitude.

The flight ended catastrophically when Brooke-Smith attempted to side-slip out of the wake and struck the ground "nose-down" at 90 mph, injuring himself seriously and heavily damaging the aircraft.

The new design retained the wings and tail of the SB.1 but (at Tom Brooke-Smith's insistence) featured two small turbojet engines housed in a new, light-alloy fuselage.