In 1943, Nazi Germany controlled almost all of Europe and much of Russia. Less than two years later the regime was in ruin, its leaders dead or imprisoned, its military reduced to scrap. To its commanders, one cause of the catastrophe stood out: the ability of the Allies to exploit their control of the air. Gerd von Rundstedt, commander of all German forces in the West, expressed the exasperation felt by many soldiers when he told his captors, in an overstatement, that air attacks had made it “impossible to bring one single railroad train across the Rhine.”
Key to making Allied airpower so overwhelming was the routine use of Republic's P-47 Thunderbolt as a swing-role fighter-bomber, sent to take on the Luftwaffe's pilots and airplanes as well as Germany's mechanized ground forces. First conceived as a high-altitude interceptor, the Thunderbolt performed so well against German fighters that few expected it to be assigned the ground-attack role in 1943, eight months after its combat debut. But its added skills and great survivability made the P-47 the most significant air weapon in the Allied push into Germany following D-Day. Developing those skills began a few months in advance of the June 6, 1944 Normandy landing.