By the late 1930s, the Germans were developing the Messerschmitt Me 163 Komet, a rocket-powered jet with speeds of up to 700 mph.
"During this time the vaunted American P-51 Mustang fighter, in comparison, topped out at less than 440 mph," according to Weapons of WWII magazine.
More than 300 Komets were built and equipped with twin 30 mm cannons. The Komet's speed was both a gift and a curse. The plane was fast enough to avoid Allied gunners but it was too fast to hit Allied aircraft.