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On which flight did the P.1 break the sound barrier?

Short answer

On its third flight: WG760 officially broke the sound barrier on its third flight, a week after its first. That was on 11 August, when it reached Mach 1.01 and became the first British aircraft to exceed the speed of sound in level flight, achieving this without using the afterburner.

Published: November 1, 2026 · Updated: November 1, 2026 · Edited by Above Ten Thousand · Editorial policy

On which flight did the P.1 break the sound barrier?
Lear Jet 23

The prototype arrives at Boscombe Down

In May 1954, WG760 and its support team moved to RAF Boscombe Down for ground taxi trials ahead of flight. On the morning of 4 August 1954, the aircraft, piloted by Roland Beamont, made its first flight from Boscombe Down. That first flight was of the P.1A prototype.

The third flight

A week later, WG760 officially achieved supersonic flight for the first time, having exceeded the speed of sound during its third flight. On 11 August the aircraft reached Mach 1.01 and became the first British aircraft to break the sound barrier in level flight. It did so without using the afterburner (postbruciatore), the reheat.

A design built for speed

Conceived to explore transonic speed and built to specification F.23/49, the aircraft had an ultra-thin wing with extreme sweep, no less than 60°. It carried two Bristol-Siddeley Sapphire turbojets stacked vertically to reduce the frontal cross-section, by 50% in that case. In the Lightning's design, engines stacked and staggered longitudinally were Petter's solution for reconciling conflicting requirements: minimising the frontal area, providing the engines with undisturbed airflow over a wide range of speeds, and housing two engines with enough thrust to reach the performance targets. The experience with the SB.5 validated the wing sweep and the low-tail configuration adopted for the P.1.

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