The Republic P-47 Thunderbolt, also known as the "Jug," was the biggest, heaviest, and most expensive fighter aircraft in history to be powered by a single reciprocating engine.  It was one of the main United States Army Air Forces (USAAF) fighters of World War II, and also served with other Allied air forces. The P-47 was effective in air combat but proved especially adept at ground attack. It had eight .50-caliber machine guns, four per wing. When fully loaded the P-47 could weigh up to eight tons. A modern-day counterpart in that role, the A-10 Thunderbolt II, takes its name from the P-47.

Initial response to the P-47 praised its dive speed and high-altitude performance, while criticizing its turning performance and rate of climb (particularly at low altitudes). Commenting on the P-47's size, British pilots joked that a Thunderbolt pilot could defend himself from a Luftwaffe fighter by running around and hiding in the fuselage. Some British assumed the American P-47 nickname "Jug" was short for "Juggernaut" and began using the longer word as an alternate nickname. Another nickname that was used for the Thunderbolt was "T-bolt".

The turbosupercharger in the P-47 gave the powerplant its maximum power at 27,000 ft (8,230 m), and in the thin air above 30,000 ft (9,144 m), the Thunderbolt became comparatively fast and nimble relative to other aircraft.

The P-47 first saw action with the 4th Fighter Group. The Group’s pilot were mainly drawn from the three British Eagle Squadrons who had previously flown the British Supermarine Spitfire Mark V. They viewed their new fighter with misgivings, at first. It was huge. Optimized for high altitude work, the Thunderbolt had 5 feet (1.5 m) more wingspan, a quarter more wing area, about four times the fuselage volume and nearly twice the weight of a Spitfire V. One Thunderbolt pilot compared it to flying a bathtub around the sky. When his unit (4th Fighter Group) was equipped with Thunderbolts, ace Don Blakeslee said, referring to the P-47's vaunted ability to dive on its prey, "It ought to be able to dive. It certainly can't climb." (Blakeslee's early-model P-47C had not been fitted with the new paddle-blade propeller). The 4th Fighter Group's commander hated the plane, and his prejudices filtered down to the group's pilots; the 4th had the fewest kills of any of the first three P-47 squadrons in Europe. The U.S. ace Jim Goodson, who had flown Spitfires with the RAF and flew a P-47 in 1943, at first shared the scepticism of other pilots for their “seven-ton milk-bottles”. But Goodson learned to appreciate the P-47’s potential: “There were many U.S. pilots who preferred the P-47 to anything else: they do not agree that the (Fw) 190 held an overall edge against it.”

The P-47's initial success in combat was primarily due to tactics, using rolls (the P-47 had an excellent roll rate) and energy-saving dive and zoom climbs from high altitude to outmaneuver German fighters. Both the Me 109 and Fw 190 could, like the Spitfire, out-turn and out-climb the P-47. But whereas both German fighters could break hard downwards, and leave the Spitfire trailing, no German piston-engined plane could out-dive the Thunderbolt. In a bounce, with their rapid acceleration downhill coupled with the pulverizing effect of eight .50s, these aircraft were deadly. The Thunderbolt was the fastest-diving American aircraft of the war—it could reach speeds of 550 mph (480 kn, 885 km/h). Major Robert S. "Bob" Johnson described the experience of diving the big fighter by writing, "the Thunderbolt howled and ran for the earth".^[18] Some P-47 pilots claimed to have broken the sound barrier, but later research revealed that due to the pressure buildup inside the pitot tube at high speeds, airspeed readings became unpredictably exaggerated. But German pilots learned soon to avoid diving with a Thunderbolt. Kurt Buehligen, a high-scoring German fighter ace with 112 victories, recalled:

"The P-47 was very heavy, too heavy for some manoeuvres. We would see it coming from behind, and pull up fast and the P-47 couldn’t follow and we came around and got on its tail in this way."

The arrival of the new Curtiss paddle-blade propeller significantly increased climb rate at lower altitudes, and came as a shock to German pilots who had resorted to steep climbs to evade pursuit by the P-47. Other positive attributes included the P-47's ruggedness; it could sustain a large amount of damage and still be able to get its pilot back to base. With eight .50 in (12.7 mm) machine guns, the P-47 did not lack for firepower. German aircraft caught in a well-aimed burst tended to fly apart from the impact of so many armor-piercing projectiles.

Although the P-51 Mustang replaced the P-47 in the long-range escort role in Europe, the Thunderbolt still ended the war with 3,752 air-to-air kills claimed in over 746,000 sorties of all types, at the cost of 3,499 P-47s to all causes in combat.^[21] In Europe in the critical first three months of 1944, when the German aircraft industry and Berlin were heavily attacked, the P-47 shot down more German fighters than did the P-51 (570 out of 873), and shot down approximately 900 of the 1,983 claimed during the first six months of 1944.^[ In Europe, Thunderbolts flew more sorties (423,435) than P-51s, P-38s and P-40s combined.

By the end of the war, the 56th FG was the only 8th Air Force unit still flying the P-47, by preference, instead of the P-51. The unit claimed 665.5 air victories and 311 ground kills, at the cost of 128 aircraft. Lieutenant Colonel Francis S. Gabreski scored 31 victories,^[24] including three ground kills, Captain Bob Johnson scored 27 (with one unconfirmed probable kill leading to some giving his tally as 28), and 56th FG Commanding Officer Colonel Hubert Zemke scored 17.75 kills. Despite being the sole remaining P-47 group in the 8th Air Force, the 56th FG remained its top-scoring group in aerial victories throughout the war.

In the Pacific, Colonel Neel E. Kearby of the Fifth Air Force destroyed 22 Japanese aircraft and was awarded the Medal of Honor for an action in which he downed six enemy fighters on a single mission. He was shot down and killed over Biak in March 1944.