In the aftermath of the Second World War, it was decided that Sweden needed a strong air defence built around the newly developed jet propulsion technology. Project "JxR" began in the final months of 1945 with two proposals from the Saab design team led by Lars Brising. The first, codenamed R101, was a cigar-shaped aircraft somewhat similar to the American Lockheed P-80 Shooting Star. The winning design however was the "barrel" design, codenamed R 1001, which proved to be both faster and more agile.
The original R 1001 was designed around a mostly straight wing, but after the Swedish engineers had obtained German research data on swept-wing designs, the prototype was altered to incorporate a 25 degree sweep, first tested on a modified Saab Safir (designated Saab 201). A member of the Saab engineering team had been allowed to review German aeronautical documents stored in Switzerland. These files captured by the Americans in 1945 clearly indicated delta and swept-wing designs had the effect of "reducing drag dramatically as the aircraft approached the sound barrier." The SAAB 29 prototype flew for the first time on 1 September 1948. It was a small, chubby aircraft with a single central air intake, a bubble cockpit and a very thin swept-back wing. The test pilot was an Englishman, S/L Robert A. 'Bob' Moore, DFC and bar, who went on to become the first managing director of Saab GB Ltd, UK, set up in 1960.
Moore described the aircraft as "on the ground an ugly duckling – in the air, a swift." Because of its shape, The Saab J 29 was quickly nicknamed "Flygande Tunnan" ("The Flying Barrel") or "Tunnan" ("The Barrel") for short. While the demeaning nickname was not appreciated by SAAB, its shortform was officially adopted. Since then, Saab named the aircraft in order to avoid it happening again. A total of 661 Tunnans were built from 1950 to 1956, making it the largest production run for any Saab aircraft.