Milt, re SR.53
Squadron Leader John S. Booth DFC was at the controls of XD145 for the first test flight, following up with the maiden flight of the second prototype XD151, on 6 December 1957. Test results indicated "...an extremely docile and exceedingly pleasant aircraft to fly, with very well harmonized controls." Both prototypes flew a total of 56 test flights, with Mach 1.33 speeds being obtained.
While testing at RAE Boscombe Down, XD151 crashed on 5 June 1958 during an aborted takeoff on its 12th flight. Running off the runway, the aircraft struck a concrete approach light, exploding on impact and killing its pilot, Squadron Leader Booth. Despite investigation by the Aircraft Investigation Board, the cause was never discovered. The take off was aborted just as the aircraft was leaving the ground, and the rocket and jet engines were cut. The investigation was unable to determine whether this was done by the pilot, or whether they had cut out through accident or failure. The remaining prototype continued to fly with Lt Cdr Peter Lamb taking over the flight test programme.