First flight of the first practical British helicopter (Weir W.5)
Tuesday, June 7, 1938 - Dalrymple, Scotland, United Kingdom
There had been two British helicopters flown earlier (Mumford at Dumbarton and Brennan at Farnborough) but this was the first truly successful aircraft. The aircraft is said to have flown 80 hours before the outbreak of World War II.
Source: "Helicopters and Autogyros of the World", Lambermont & Pirie