What does "Jug" mean?

As the P-47 reached operational status it earned a nickname, "Jug," because its profile resembled a common milk jug of the time. To ground crews, the Thunderbolt's thick, bottle-shaped fuselage recalled a glass milk jug of those years.

A more romantic explanation holds that "Jug" was short for "Juggernaut," a reference to its size and hitting power. That variant was happily adopted by wartime public-information services. Neither origin is firmly documented, so the milk-jug shape is the safer bet, with "juggernaut" treated as folk etymology.

The design started with the powerplant: instead of drawing an airframe and then looking for an engine to fit, Kartveli began with the huge 18-cylinder, turbosupercharged Pratt & Whitney R-2800 Double Wasp. That twin-row radial produced up to 2,000 hp (1,500 kW) and drove a four-blade, constant-speed Curtiss Electric propeller 146 in (3.7 m) in diameter. The air-flow system was designed first, and the fuselage structure was built around it. The Thunderbolt's defining feature was its exhaust-driven turbosupercharger, housed inside the fuselage about 22 feet behind the propeller. Gases traveled from the engine to the turbine through jacketed ducts under the fuselage, and the compressed intake air passed through an intercooler before entering the carburetor. To accommodate the large-diameter propeller without giving up wing armament or structural efficiency, Republic developed a telescoping main landing gear that, when retracted, shortened by nine inches.