In the late 1950s, the Soviet Air Defence Forces had a problem. The American B-58 Hustler had just entered service. The B-70 Valkyrie was on the drawing board. Both could cruise at Mach 2 or above, both could carry nuclear weapons, and both could outrun anything the PVO Strany had in its inventory. Mikoyan-Gurevich was asked, in the late 1950s, to design an interceptor that could climb to 22,000 metres, hold position there, and engage hostile bombers at velocities the world had not yet flown.

The answer was the Ye-150. On 8 July 1960, with senior test pilot Aleksandr Fedotov at the controls, the prototype lifted off Akhtubinsk. By 1961 it had reached 2,890 km/h — Mach 2.65 — at 19,100 metres. It was the fastest, highest-flying single-engined fighter the Soviet Union had ever built. Most aviation enthusiasts have never heard of it. There is a reason for that.

Designing Mach 2.5

The Ye-150 was one of Mikhail Gurevich’s last major aircraft designs — Gurevich himself was 67 when the prototype flew, and he retired in 1964. The design problem was severe. At Mach 2.65 the leading edges of an aircraft heat to roughly 220 °C from skin friction alone. Aluminium softens beyond 150 °C; the structure has to be made of either steel or titanium, neither of which the Soviet Union could fabricate at the scale required for a production fighter in 1960. Gurevich split the difference. The Ye-150 used a primarily aluminium airframe but with steel structural members at the leading edges, the engine intake, and the rear fuselage where heat soak from the engine was most severe.

The engine was the single biggest challenge. The Tumansky R-15-300 was a brand-new high-temperature afterburning turbojet developed specifically for the Ye-150. It produced some 10,150 kilograms (22,400 lbf) of thrust in afterburner — more than any other Soviet engine of the era — but had a service life of only about 50 hours between overhauls when it first entered test. The engine eventually became reliable. But not in time to save the Ye-150 programme.

The automated interceptor concept

The Ye-150 was designed to be flown, in combat, almost entirely under ground control. The Soviet PVO Strany operated a comprehensive air defence radar network — the largest in the world by the early 1960s — and Gurevich’s design assumption was that the pilot would take off, climb under ground-directed vectoring, accelerate to Mach 2.65, fire a single long-range air-to-air missile under autopilot guidance, and return to base with very little manual intervention. The pilot was essentially a system manager, not a fighter pilot in the conventional sense.

The aircraft carried two Kaliningrad K-9 air-to-air missiles — at the time the most ambitious Soviet AAM, with a semi-active radar homing seeker. The K-9 was developed in parallel with the Ye-150 and was as troubled. Together, the airframe, engine, and weapon were an extraordinary technological gamble: three high-risk technologies dependent on each other for the system to work at all.

Why it was cancelled

By 1962, the Ye-150 family had achieved most of its design targets. The Ye-152-1 — registered with the FAI under the cover designation Ye-166 — set three official world records: an absolute speed record of 2,681 km/h, a 100 km closed-circuit record of 2,401 km/h, and a sustained-altitude record of 22,670 metres. The aircraft worked. It would have entered service as the world’s first Mach 2.65 single-engined interceptor.

Then in 1961 the United States cancelled the B-70 Valkyrie as a production bomber, cutting it back to a research programme. The Soviet threat hierarchy reshuffled almost overnight. The new top priority was no longer Mach 3 bombers — it was reconnaissance aircraft like the U-2 and SR-71, and low-flying cruise missiles. The Soviet Air Defence Forces decided they needed a twin-engined, longer-ranged interceptor instead of a single-engined point-defence Mach 2.65 specialist. Mikoyan was instructed to develop the Ye-155 — a twin-engined design based on the same R-15 powerplant — and the Ye-150 programme was wound down.

The Ye-155 became the MiG-25 Foxbat, which entered service in 1970 and became one of the iconic aircraft of the Cold War. The Foxbat’s steel airframe, its R-15 engines, its short-life high-temperature construction philosophy, its automated ground-controlled interception doctrine — all of these came directly from the Ye-150. The single-engined prototype died so the twin-engined production aircraft could live.

Aviation historian Yefim Gordon credits the Ye-150 family as the direct technical foundation of the MiG-25: the major engineering decisions of 1959–1962 were repeated, with modification, in the Foxbat — one of the most consequential prototype programmes in Soviet aviation history, despite never entering service.

Yefim Gordon — Soviet aviation historian, author of Soviet Heavy Interceptors (2004)

The aircraft you have never seen

Only one Ye-150-family airframe survives. The Ye-152M is on outdoor static display at the Central Air Force Museum at Monino, near Moscow — visible to anyone who makes the difficult trip to the museum but unknown to almost everyone else. The twin-engined Ye-152A was lost in a crash in 1965. The Ye-150 prototype itself did not survive.

For three years in the early 1960s, the fastest single-engined fighter in the world wore Soviet stars on a hidden test range outside Akhtubinsk. The aircraft set world records. The aircraft was then quietly cancelled, parted out, and folded into the production line of a different aircraft. The Foxbat got the fame. The Ye-150 got the engineering bills.

Sources: Central Air Force Museum (Monino), Yefim Gordon “Mikoyan Ye-152 / Ye-152A / Ye-152M” (Midland Publishing 2006), Hush-Kit Aviation World, Aviation Week archives.