Whilst commercial jet transports began to enter service after World War 2, aiming for a supersonic airliner was a remote dream, until Convair developed their Mach 2 B-58 bomber. The dreams revived. Some studies proposed a B-28-like aircraft with a detachable passenger pod slung below it. Britain set up the Supersonic Transport Aircraft Committee in 1956, and in 1959 they favoured two main types of SST (supersonic transport). One was a radical Mach 1.2 transport with a double-kinked M-shaped wing plan, and the other was a longer range, larger Mach 1.8 aircraft, a slender delta design.

These designs were considered to be about as far as such an aircraft could go with a traditional aluminium-alloy airframe. In the USA, steel sandwich structures were already being used. The XB-70 Valkyrie would use stainless steel, and the A-12 Blackbird used titanium.

When it became clear, from 1962, that the Anglo-French SST, to be named Concorde, would actually go ahead, other nations began to work on designs of their own. In the USSR, the Tupolev design bureau began working on their Tu-144. America could hardly stand by, and in 1962 NASA began the SCAT (Supersonic Commercial Air Transport) program.

The SST program gained impetus when, in a speech delivered on 5th June, 1963, President John F. Kennedy announced that such a program was authorised. The Federal Aviation Authority issued a Request for Proposals for an SST design to three airframe and three engine manufacturers - Boeing, Lockheed, North American, Curtiss Wright, General Electric and Pratt & Whitney. The designs were submitted to the FAA on January 15th, 1964.
Unlike everyone else, the Americans would aim for a Mach 3 (2,000 mph) airframe of steel or titanium.

Boeing had quietly worked on a concept for an SST aircraft since 1952, as part of the project work which goes with corporate forward-thinking. In 1958 they had set up a small group to concentrate entirely on developing an SST design, and by 1960 were spending over $1m annually on it. Using Boeing Model no. 733, they came up with a few alternative proposals.

Most of their options involved delta-wing designs. The work of another Boeing team on a design for a TFX tactical fighter with variable sweep wings (later to be shelved in favour of the the General Dynamics F-111) drew their attention to the benefits of a variable geometry.

During 1960 a "competition" was held within the Boeing SST group between the delta and variable-sweep configurations, looking to a 150-seat aircraft capable of non-stop flight between Western Europe and the Eastern US. The variable sweep option emerged substantially ahead.

This was the design which Boeing submitted to the FAA for evaluation against the delta design of Lockheed's L-2000. A tentative Model 2707 was used to designate the design, but mostly Boeing simply called it their "1966 model". It was submitted to the FAA in early 1964 as the Model 733-197. The FAA initiated further studies of proposals submitted by Boeing, Lockheed, GE and P&W, the results of which were submitted that November. By now Boeing's design had become the Model 733-290, with 250 seats.

Final design submissions were next sought by the FAA, and Boeing produced the 733-390, with a capacity for up to 300 passengers. By the final phase, in September 1966, Boeing was working with an even larger design, for up to 300 passengers. They had built a mock-up of the aircraft by now. It was the last day of 1966 when the final design was chosen. It was the Boeing design.

The mock-up of the variable-geometry aircraft was 306 feet long (91.8 m.). It showed both Pratt & Whitney JTF17A and General Electric GE4/J5 engine pods, with the latter being selected by the FAA for development along with the Boeing SST.

The wings on the mock-up could be moved, manually from fully aft, with a 72° ;eading edge sweep, to fully extended, with a 30° sweep. A design modification brought the forward sweep forward to 20° for better take-off and landing performance. A benefit of variable geometry was, of course, the ability to take off and land at lower speeds and in less distance than would a comparable fixed wing aircraft.

Seating was to be seven abreast, two seats each side with three in the centre, and two aisles. The mock-up was fitted with 277 seats (30 first-class and 247 tourist). The impression on entering the cabin was that the so-called "narrow" part of the fuselage was noticably wider (about 4 ft or 1.22 m) than any contemporary jet transport. The cabin length was interrupted by two galley/toilet areas. Wardrobe racks, galley tray containers and bar units could be removed from stowed positions and wheeled up and down aisles. Overhead luggage racks included restrainers, and were capable of housing items which usually had to be stowed under passengers' feet.

Boeing mocked up two possible forms of inflight entertainment; retractable TV screens in the overhead luggage racks at every sixth row, or small permanent screens in consoles between the paired first-class seats. Windows had an external diameter of only 6 inches, but the 12 inch internal diameter gave an illusion of size. Rather than sun blinds, Boeing proposed a rotatable inner panel of polarised glass. Seats were the company's own design, and claimed to adjust to adults up to 6 ft. 7 in. (2.0 m) tall. In addition to underfloor holds, there was a large baggage compartment to the rear of each cabin.

Like the Concorde the SST had a variable nose geometry to improve flight deck forward views on approach. Boeing used a double-hinge, with the section forward of the cockpit angling down but the nose cone maintaining a similar axis to that of the fuselage. With the nose raised, minimum ground clearance was 8 ft. 9 in (2.67 m), reducing to only 4 feet (1.22 m) with it lowered.

Boeing predicted that if design and construction of prototypes began in early 1967, the first flight could be made in early 1970. Design and fabrication of production aircraft could begin in early 1969 with the flight testing in late 1972. The first aircraft could then be certified and introduced to airline service in mid-1974. By 1980 the company estimated there would be a market for a larger Model 390-475 SST, with between 700 and 1,000 aircraft being required.

The Boeing variable-geometry SST dream was never realised. The variable-sweep idea was abandoned in October 1968, and the 2707-300 was cut to 234 seats, with a fixed gull wing mounted ahead of a horizontal tail. It used essentially the same fuselage and engines as the preceding version.

Two prototypes were begun in September 1969 but, amid a general US protest against Concorde, the US Senate closed down the SST program completely on 24th March, 1971, possibly the first time the US had backed away from a potentially huge market.

The Russian Tu-144 entered cargo service in 1975, despite the crash of the second pre-production aircraft in Paris in 1973. After another accident production ceased in June 1978. The Concorde first flew on 2nd March, 1969. It entered service between London, Paris, Bahrain, and Rio/Dakar. The obvious destination, New York, refused to admit the foreign SST until 24th May, 1976.