an unlicenced copy of the R-1830. The B 17B used a Bristol Mercury XXIV built by Svenska Flygmotor AB (SFA) in Sweden, and the B 17C used an imported Piaggio P.XI radial from Italy. The United States government denied a request to purchase a licence to build the Twin Wasp, so an unlicensed, reverse engineered copy was built instead as the STWC-3 (Swedish Twin Wasp C-3) to supplement and replace the lower powered Mercury radials already being built under licence. Until production caught up to demand, the earliest aircraft being delivered were flown to their destinations, the engines were removed and shipped back, to be used on the next aircraft to be delivered. Operational history The first flight was on 18 May 1940 and first deliveries of dive bombers to the Flygvapnet began in March 1942, while deliveries of reconnaissance versions began in June 1942, and the type was operational by September 1942 when the first exercises were carried out. Problems immediately arose with wing failures, and additional modifications were needed before it could be cleared for dive bombing, which remained limited to shallow attacks thereafter. The final aircraft was delivered on 31 August 1944. A B 17 was used to test the ejection seat Saab had developed for use in the Saab 21 pusher fighter, which was first successfully fired on 27 February 1944 with a dummy. Stig Wennerström gained some fame in Sweden for successfully bailing out from a B 17 from low altitude, with his gunner, but would later become a spy for the Soviet Union. For several months in late 1944 and early 1945 fifteen B 17As were operated by the Danish Brigade in Sweden (Danforce) a unit of 5000 men (including 50 airmen) in Sweden which had been formed to assist in liberating occupied Denmark from the Nazis, and preventing the retreating German soldiers from using civilians as human shields, and carrying out scorched earth tactics as they had done elsewhere. However, due to the German surrender on 7 May 1945, the aircraft were no longer needed and were returned to Flygvapnet control a couple of months later. Rapid advances in aviation related to improved aerodynamics, higher engine power and finally the introduction of jet engines, resulted in it having a short career, and it was gradually withdrawn from frontline service between 1948 to 1950, while the last examples were retired from secondary roles by