WK163 had one special feature. Instead of the Rolls-Royce Olympus engines that had helped earlier Canberras climb to record height, this had something even more powerful – rockets. WK163 had been fitted with an experimental new powerplant, the Napier Double Scorpion, which was housed in the aircraft’s bomb bay. The idea was that the rocket’s extra thrust could help keep the aircraft aloft in the thin air found more than 60,000ft (20km) above the Earth’s surface, or even higher.

The pilot, Mike Randrup, flew with the rocket motor’s inventor, Walter Shirley, along for the ride. As they were expected to fly higher than previously thought possible, both wore pressure suits.

Randrup flew the plane up to 44,000ft using its normal engines, a pair of Rolls-Royce Avons mounted in the thick wings. He pointed the aircraft into a steep climb and turned on the rocket motor. The Canberra soared higher and higher, past 60,000ft… 65,0000ft… 70,000ft.

The aircraft was now heading into air so thin that the minimum speed need to keep it in the air – its stall speed – and the speed where supersonic shock waves started to form along its wings began to converge. The convergence could cause the plane to shake apart, miles above the English countryside. Randrup had to keep the aircraft in a 15mph window, all the while climbing steadily higher and higher.