In the late 1950s, both superpowers reached the same conclusion: the future of strategic bombing was speed. Build a bomber that flies at Mach 3 and nothing can catch it. No interceptor, no missile, no air defence system could touch an aircraft crossing the sky at three times the speed of sound and 70,000 feet above the earth. America built the XB-70 Valkyrie. The Soviet Union built the Sukhoi T-4 "Sotka." Both were technological masterpieces. Both were cancelled. And together, they represent the most expensive dead end in aviation history. We've written about both aircraft individually before — the Sukhoi T-4 and the Valkyrie each deserve their own deep dives. This piece puts them side by side.

The American Vision

North American Aviation began designing the XB-70 in 1957 under a USAF requirement for a bomber that could penetrate Soviet airspace at Mach 3+, deliver nuclear weapons, and return home before anyone could react. The aircraft that emerged was staggering in scale: 56 metres long, a 32-metre wingspan, six General Electric YJ93 turbojet engines, and a maximum takeoff weight of nearly 246 tonnes. The Valkyrie used compression lift — its wingtips folded down at supersonic speeds to ride its own shock wave — a concept so advanced that no production aircraft has used it since. On October 14, 1965, XB-70 Ship 1 reached Mach 3.02 at 70,000 feet — Ship 2 later pushed that to Mach 3.08. For a brief moment, America had the fastest and highest-flying bomber on earth.

The Soviet Response

When Soviet intelligence learned about the XB-70 programme in the early 1960s, the response was immediate. The Sukhoi Design Bureau was tasked with building a comparable aircraft — one that could serve as both a strategic bomber and a high-speed reconnaissance platform. The T-4 "Sotka" (meaning "hundred," a reference to its original 100-tonne weight target) first flew on August 22, 1972 — nearly eight years after the Valkyrie's maiden flight. It was smaller than the XB-70: 44 metres long, 22-metre wingspan, four Kolesov RD-36-41 engines, and a takeoff weight of 135 tonnes. But in one critical respect it was more advanced: the T-4 featured a quad-redundant fly-by-wire flight control system with full three-axis stability augmentation and auto-throttle — technology that would not become standard in Western fighters for another decade. The T-4 also featured a distinctive droop nose — like Concorde's — that lowered for takeoff and landing to give the pilots forward visibility, then raised flush with the fuselage for supersonic flight.

What Killed Them

The same thing killed both programmes: surface-to-air missiles. By the mid-1960s, the Soviet Union had deployed the SA-2 Guideline and was developing the SA-5 Gammon. Both could engage targets above 60,000 feet. The Valkyrie's entire concept — fly high and fast and nothing can touch you — was suddenly obsolete. If a missile can reach your altitude and calculate your trajectory, Mach 3 is not fast enough. The XB-70 programme was downgraded from a bomber to a research aircraft in 1961. Ship 2 was destroyed in a midair collision with an F-104 chase plane in June 1966, killing F-104 pilot Joe Walker and XB-70 co-pilot Carl Cross (XB-70 pilot Al White ejected and survived). Ship 1 continued flying as a NASA research platform until February 1969. The T-4's fate was arguably worse. Political infighting between Sukhoi and Tupolev — whose Tu-22M "Backfire" was cheaper, simpler, and closer to production — doomed the programme. The T-4 made only ten flights, never exceeding Mach 1.36 — far short of its Mach 3 design target. The programme was cancelled in December 1975. The sole surviving prototype sits in the Central Air Force Museum at Monino.

The Real Legacy

Neither the XB-70 nor the T-4 ever dropped a bomb. But both programmes generated enormous technological dividends. The Valkyrie's research flights produced data on supersonic aerodynamics, thermal effects, and structural loads that fed directly into the B-1 Lancer programme. The T-4's fly-by-wire system and titanium construction techniques influenced every subsequent Sukhoi fighter, from the Su-27 to the Su-57. The arms race logic was pure Cold War: America builds the ultimate bomber, the Soviet Union builds the ultimate counter, both sides realise the concept is obsolete, both cancel. The only winners were the engineers. Sources: USAF Museum, MilitaryFactory, National Interest, Key Aero, Air Data News