Saab’s early jet studies used a conventional straight wing. That changed when the company’s research chief, Frid Wänström, returned from Switzerland in 1945 with German aerodynamic data showing the drag-reducing benefits of wing sweep at high speed. Sweden’s Royal Institute of Technology and its aeronautical research institute ran the numbers and wind-tunnel tests, and Saab committed to a 25-degree swept wing — a bold choice for a country building only its second jet.

The gamble paid off. The Tunnan became the first swept-wing fighter to enter service in Western Europe, beating Britain’s Hawker Hunter and France’s Mystere into squadron use. It was inspired by German work — the unbuilt Messerschmitt P.1101 is often cited — but it was designed, tested and manufactured entirely in Sweden, and it put a small neutral nation at the leading edge of jet fighter design.

The nickname was an engineering consequence, not a styling choice. The de Havilland Ghost was a centrifugal-flow turbojet — a design that is short but wide, because air is flung outward through the compressor before combustion. Wrapping a slim, streamlined fuselage around such an engine was impossible, so Saab built a short, deep, rounded body with a circular nose intake feeding straight into the engine face. The workers called the resulting shape the flygande tunnan, the flying barrel, and the name stuck. Fatter axial-flow engines would later let designers slim fighters down, but in 1948 the barrel was simply the honest shape for the powerplant available.

For a supposedly ungainly aircraft, the Tunnan was genuinely fast. On 6 May 1954 Captain Anders Westerlund set an international 500 km closed-circuit record at 977 km/h in a standard J 29. The following year, on 23 March 1955, Hans Neij and Birger Eriksson took a two-aircraft flight to a 1,000 km closed-circuit record of 900.6 km/h. These were not stunt machines but production fighters, and the records were a pointed reminder to the great aviation powers that a small neutral country could build a jet fully competitive with their own.

The Tunnan was a Swedish state-funded product built for the Flygvapnet, not an item sold on an open export market at a published price, so no reliable flyaway unit cost or cost-per-flight-hour figure exists in the public record. What is documented is scale: with roughly 660 built, it remains the most-produced aircraft in Saab’s history, and its long service — front-line into the mid-1960s and in target-towing and other second-line roles into the mid-1970s — suggests it was cheap and robust to operate by the standards of its day. Any precise dollar or krona figure attached to a Tunnan should be treated as an estimate.