Before the United States entered World War II it was eagerly digesting the results of air combats in Europe and, in 1940, existing plans by Republic's chief designer, Alexander Kartveli were urgently replaced by sketches for a much bigger fighter with the new R-2800 engine. This appeared to be the only way to meet the Army Air Corps' new targets for fighter performance. Kartveli began by designing the best installation of the big engine and its turbocharger, placed under the rear fuselage. The air duct had to pass under the elliptical wing, and there were problems achieving ground clearance for the big propellor (12 feet in diameter, even though it had the unprecedented total of four blades) with landing gear able to retract inwards and still leave room in the wings for the formidable armament of eight 0.5 inch machine guns.

After severe and protracted technical difficulties the P-47B was cleared for production in early 1942 and at the beginning of 1943 two fighter groups equipped with the giant new fighter (one being the famed 56th, who went on to become top scorers in Europe) joined the 8th AF in Britain to begin escorting B-17 and B-24 heavies. Their value was dramatically increased when they began to carry drop tanks and fly all the way to the target. The same capability turned the big and formidable fighter into a much-feared bomber and, with devasting firepower, vast numbers of P-47Ds strafed and bombed their way through the European and Pacific theatres until the end of World War II. Republic's output of D models (12,602) is the largest total of one sub-type of any fighter in history, total production of the "Jug" (as it was affectionately christened by its pilots) amounting to 15,660. The lightweight M was too late for its role of chasing flying bombs but scored successes against the Me 262 and Ar 234 jets, while the long-range P-47N matched the M fuselage with a bigger wing for the Pacific war. After World War II the "Jug" proved extremely popular with many air forces around the world well into the 1950s.