Heinkel He 280: Germany's Heinkel He 280 was the first fighter plane in the world to be propelled by a turbojet engine. It first flew in 1940 and had a top speed of 559 miles per hour, with a maximum altitude of 37,730 feet.

In 1940, the concept of a "jet" was still in its experimental infancy, and the fastest jet-powered aircraft was the Heinkel He 178. This German aircraft made history on August 27, 1939, as the world's first turbojet-powered airplane to fly. By 1940, it remained the pinnacle of jet technology, reaching a top speed of approximately 373 miles per hour (600 km/h). While this was impressive for the time, it was actually slower than the top-tier propeller-driven fighters of 1940, such as the Messerschmitt Bf 109 or the Supermarine Spitfire, which could exceed 400 mph in level flight. The He 178 was strictly a technology demonstrator and never saw combat. It wasn't until later in the decade that jet technology matured with the Messerschmitt Me 262, which eventually pushed speeds toward 540 mph. In 1940, if you were looking for the "fastest" aircraft overall, you would be looking at piston-engine planes; the jet was a experimental curiosity that had yet to prove it could outpace the refined aerodynamics of the traditional fighter planes of the early World War II era.