The Saab 29 Tunnan, colloquially Flygande tunnan or just Tunnan (, "The barrel"), is a Swedish fighter that was designed and manufactured by Saab in the late 1940s. It was the second turbojet-powered combat aircraft to be developed in Sweden, the first being the Saab 21R, and it was the first Western European fighter to be produced with a swept wing post World War II, only being preceded in Western Europe as a whole by the Me 262 built during the war. Despite its rotund appearance, from which its name is derived, the J 29 was fast and agile and served effectively in both fighter and fighter-bomber roles into the 1970s. Development Sweden had fallen behind the rapid technical progress being made elsewhere, and Saab needed to catch up in terms of aerodynamics and jet propulsion. Accordingly, project "JxR" was initiated in late 1945 and requirements were drawn up in October 1945. A pair of proposals were presented by the Saab design team, led by Lars Brising. The first of these, codenamed R 101, nicknamed cigarren (the cigar) due to its shape, bore a strong resemblance to the American Lockheed P-80 Shooting Star. The second design, which was chosen, was the barrel-shaped design, codenamed R 1001, which proved to be both faster and more agile. The R 1001 concept had a straight wing, but after the engineers obtained German swept-wing research data, it was given a 25 degree sweep. Information on swept-wings came through Switzerland and included drawings for the Messerschmitt P.1101, P.1110, P.1111 and P.1112. SAAB's project manager, Frid Wänström, collected these documents in 1945 from Messerschmitt engineers who escaped to Switzerland at the end of the War. Among them were engineer and aerodynamicist Hermann Behrbohm, who joined Saab's J 29 team. These documents clearly indicated delta and swept-wing designs "reduc[e] drag dramatically as the aircraft approached the sound barrier." To make the wing as thin as possible, the undercarriage retracted into the fuselage, rather than the wings. Wind tunnel testing at the Swedish Royal University of Technology and by the National Aeronautical Research Institute also influenced its aerodynamics. These tests determined the required fuselage form to ensure it could attain the targeted critical Mach number, as well as supporting the use of a straight-through airflow to maximize thrust. Automatically locking leading edge slots, interconnected with the flaps, were also deemed necessary for lateral stability during take-off and landing.