To further verify the swept wing, a Saab Safir was modified with a full-scale wing as the Saab 201. The finalized design, incorporating the new information was drawn up in January 1946. The original powerplant was to have been the de Havilland Goblin turbojet, however, in December 1945, the more powerful de Havilland Ghost became available. This was ideal as not only was the Ghost set up for a circular air intake, its diameter would fit within the planned fuselage. Following negotiations between de Havilland and Saab, the Ghost engine was selected to power the type. Despite early doubts for the supply of an equivalent to the American 75S aluminium alloy, Svenska Metallverken was able to manufacture it, although significantly larger sections were used than typical for aircraft construction. The structure employed heavy frames and stressed skin to meet conflicting requirements on space, strength, rigidity and accessibility. The Swedish Air Force requested verification of the performance and a production plan for the project in February 1946. In Autumn 1946, the Swedish Air Force formally ordered three prototypes, with the type designation J 29. Static testing of the full-scale mock-up revealed problems with pressure cabin leaks, and aileron behavior. A hydraulic system was installed to solve the latter issue. However these delayed the first flight until after the hoped for date of 1 August 1948. The first flight by a Saab 29 prototype was on 1 September 1948, was made by S/L 'Bob' Moore, who was later the first managing director of Saab GB, UK. A problem with the landing gear affected the expected top speed of the aircraft. Following the flight, Moore described the aircraft as "on the ground an ugly duckling – in the air, a swift." Because of the shape of its fuselage, the Saab J 29 quickly received the nickname Flygande Tunnan ("The Flying Barrel"), or Tunnan ("The Barrel") for short. While not appreciated by SAAB, its short form was eventually adopted officially. Four prototypes were built for the test program. The first two lacked armament, carrying heavy test equipment in their place instead. The third was armed with four cannons. Air brakes on the fuselage and on the wings behind the rear spar and both conventional and combined aileron/flap arrangements were tested. Flight tests revealed that the J 29 prototypes could exceed the maximum Mach number for which they had been designed and flight performance figures