In February 1965, the new Labour government cancelled the Hawker Siddeley P.1154 — a Mach 1.7 vectored-thrust VTOL strike fighter that was, by every metric that mattered, the aircraft the F-35B would eventually try to be. Forty-five years later. With a vastly more expensive engine. And without the elegance.

The P.1154 grew out of NATO's 1961 NBMR-3 specification, which demanded a supersonic VTOL strike fighter that could disperse to forest clearings and bombed-out runways. Hawker's chief designer Sir Sydney Camm and engine man Stanley Hooker at Bristol Siddeley took the same vectored-thrust trick that powered the subsonic P.1127 (later the Harrier) and scaled it brutally upward. The engine — the BS.100 — was a 33,000 lb-thrust vectored turbofan with plenum chamber burning: raw fuel injected into the cool front nozzles and ignited, boosting thrust roughly 50% for the supersonic dash. Four swiveling nozzles, no separate lift engines, no auxiliary fans, no clutches. Just one engine doing every job.

The NBMR-3 competition was won by the P.1154 in 1962. NATO promptly refused to standardize on it because France wanted its own Mirage III-V. Britain pressed on anyway, funding a joint RAF strike version and a Royal Navy fleet defense variant. Then the Navy walked away in 1964 over thrust margins on a hot day in the Indian Ocean and bought F-4 Phantoms instead. The RAF version survived another year. The first prototype was 80% complete at Kingston when Defence Secretary Denis Healey killed it on 2 February 1965, citing cost and the Phantom's availability. Britain bought F-4s and developed the subsonic Harrier as a consolation. The supersonic vectored-thrust fighter would not fly anywhere in the world until the F-35B in 2008.

Why modern technology makes it viable now:

• Plenum chamber burning is no longer exotic. Modern FADEC, ceramic matrix composite combustor liners, and active clearance control solve the 1960s nightmares of thermal distortion and nozzle erosion that frightened Bristol engineers. Rolls-Royce has run vectored-thrust testbeds on the Pegasus successor lineage continuously since.
• Carbon-fiber airframes eliminate the weight-growth spiral that ate the P.1154's margin. The original design was aluminum and titanium; a modern equivalent would be 30% lighter for the same structural job, restoring the vertical-takeoff bringback that doomed the Navy variant.
• The F-35B proved the concept and the customer. Lockheed's LiftSystem uses a 27,000-lb shaft-driven fan plus a swiveling rear nozzle — a Rube Goldberg solution costing ~$135M per aircraft. A single-engine vectored design with PCB has fewer moving parts, no driveshaft, no clutch, no lift-fan doors. The thermal signature on deck is the only real disadvantage, and modern deck coatings already handle it.
• Digital flight control ends the transition-regime instabilities that killed three test pilots in early Harrier development. The P.1154's mechanical reaction-control system was its hardest engineering problem; today it's a software task.

The P.1154 was not a fantasy. It had an engine on a test stand, an airframe on jigs, NATO competition wins, and signed contracts. Britain spent £21 million (roughly £500M today) developing it and threw the lot away for a Phantom buy that cost more per aircraft than the P.1154 would have. The aircraft we built instead — the Harrier — became a legend by being subsonic. Imagine what the supersonic one would have been.