While the Concorde and Tupolev Tu-144 grabbed the supersonic headlines, few remember that the United States was building something far more ambitious: a 300-passenger, Mach 2.7 titanium airliner with a swing-wing design that would have made the Concorde look like a regional commuter. The program ran from 1963 to 1971, consumed roughly $1 billion in 1971 dollars (about $7.7 billion today), and was killed by a single Senate vote — 51 to 46 — on March 24, 1971.

The story begins with President Kennedy's June 1963 speech at the Air Force Academy, where he committed the U.S. to a supersonic transport partly in response to the Anglo-French Concorde announcement. The FAA ran a design competition. Lockheed proposed the L-2000, a fixed delta-wing aircraft. Boeing proposed the Model 733, evolved into the 2707-200, featuring a variable-geometry swing wing — swept back for Mach 2.7 cruise, swept forward for low-speed takeoff and landing on conventional runways.

Boeing won in December 1966. The specifications were staggering:

• Cruise speed: Mach 2.7 (~1,800 mph)
• Range: 4,000 nautical miles
• Capacity: 277-300 passengers (vs. Concorde's 100)
• Skin temperature at cruise: 232°C — too hot for aluminum, requiring titanium for 93% of the airframe
• Engines: Four General Electric GE4/J5 afterburning turbojets, 69,900 lbf thrust each

The swing wing proved the program's undoing. Boeing's engineers discovered that the pivot mechanism, hydraulics, and structural reinforcement added over 13,600 kg of weight — wiping out payload margins. In 1968, Boeing capitulated and switched to the 2707-300: a fixed delta-wing tailed configuration. Two prototypes were ordered. Then came the headwinds.

Environmental concerns crystallized around sonic boom (which forced subsonic-only overland flight, killing the economics), stratospheric ozone depletion from NOx emissions, and airport noise. William Shurcliff's Citizens League Against the Sonic Boom mobilized public opinion. Senator William Proxmire led the funding cancellation in Congress. On March 24, 1971, federal funding ended. Boeing laid off 60,000 workers in Seattle — the famous "Will the last person leaving Seattle turn out the lights?" billboard appeared that year.

Why it deserves a second look in 2026: Every technical objection that killed the 2707 now has an answer:

• Sonic boom: NASA's X-59 QueSST, flown in 2024, demonstrated boom reduction to ~75 PLdB — a "thump" quieter than a car door slam. The FAA is rewriting overland supersonic rules in 2026.
• Titanium fabrication: Additive manufacturing and superplastic forming have collapsed costs that were ruinous in 1970. SpaceX prints titanium engine parts routinely.
• NOx emissions: Modern combustor designs (lean-burn, staged) achieve emissions Boeing's 1971 engineers couldn't dream of.
• Fuel burn: Sustainable aviation fuel (SAF) addresses the carbon argument that Boom Supersonic now wrestles with.
• Computational aerodynamics: CFD that took weeks on a CDC 6600 now runs in hours on a workstation, enabling shapes Boeing literally could not analyze.

Boom Supersonic's Overture targets 64-80 passengers at Mach 1.7. The 2707 was aiming at four times that capacity at 50% higher speed. The 1971 vote didn't kill supersonic travel because it was impossible — it killed it because the engineering challenges of that decade made the economics impossible. Those challenges no longer apply.