The Walter HWK 109-509 powered the first piloted aircraft of any type to exceed how many MPH in level flight?
Walter HWK 509: The Walter HWK 109-509 was a German liquid-fuel bipropellant rocket engine that powered the Messerschmitt Me 163 Komet and Bachem Ba 349 aircraft. Messerschmitt Me 163 Komet: The Messerschmitt Me 163 Komet was a German rocket-powered fighter aircraft. Messerschmitt Me 163 Komet:  Designed by Alexander Lippisch, it is the only rocket-powered fighter aircraft ever to have been operational and the first piloted aircraft of any type to exceed 1000 km/h (621 mph) in level flight.
621