The most-repeated explanation is the simplest: the Thunderbolt’s fat, bottle-shaped fuselage reminded ground crews of a glass milk jug of the era. A more romantic story holds that “Jug” was short for “Juggernaut,” a nod to its size and hitting power — a version happily embraced by wartime public affairs. Neither origin is firmly documented, so the milk-jug shape is the safer bet, with juggernaut treated as folk etymology. Either way the nickname stuck, and no P-47 pilot ever seemed to mind it.

The R-2800 Double Wasp was an 18-cylinder, two-row air-cooled radial rated at about 2,000 hp for take-off, and up to roughly 2,400–2,500 hp with water injection on late P-47D engines. Its high-altitude secret was the ducting: ambient air entered under the engine, was compressed and heated by the rear-fuselage turbo-supercharger, passed through an intercooler venting out the fuselage sides, and only then reached the carburettor. The system was heavy and complex, but it kept the engine breathing thin air at 30,000 ft — where the Jug fought best and dived like a stone.

Once the P-51 took over long-range escort in late 1943, the Thunderbolt turned to the ground war and dominated it. Across the European theatre USAAF Thunderbolts are credited with wrecking on the order of 9,000 locomotives, 86,000 railway cars, 68,000 trucks and 6,000 armoured vehicles. The Brazilian squadron alone claimed 1,304 vehicles, 250 railway cars and 25 bridges. Eight fifties, up to 2,500 lb of bombs and rockets, and an airframe that could absorb ground fire made the Jug the aircraft German drivers feared on every road in daylight.

In wartime dollars the Thunderbolt cost roughly $85,000 per aircraft at the 1944 flyaway price — cheaper than a P-38 Lightning and comparable to a P-51 Mustang, with early examples costing more. Because the type left frontline service decades ago, there is no meaningful modern cost-per-flight-hour figure: only a handful of airworthy warbirds survive, and their owners burn expensive avgas through a thirsty 2,000-hp radial. Any precise operating cost you see quoted for a flying P-47 today is a private estimate, not a published rate.