May 24, 1940

1940Igor Sikorsky performs the first successful single-rotor helicopter flight.^[†]

Igor Ivanovich Sikorsky was a Russian-American aviation pioneer in both helicopters and fixed-wing aircraft. His first success came with the Sikorsky S-2, the second aircraft of his design and construction. His fifth airplane, the S-5, won him national recognition and F.A.I. pilot's license number 64. His S-6-A received the highest award at the 1912 Moscow Aviation Exhibition, and in the fall of that year the aircraft won first prize for its young designer, builder and pilot in the military competition at Saint Petersburg. In 1913, the Sikorsky-designed Russky Vityaz (S-21) became the first successful four-engine aircraft to take flight. He also designed and built the Ilya Muromets family of four-engine aircraft, an airliner which he redesigned to be the world's first four-engine bomber when World War I broke out.

1940Acting on the orders of Soviet leader Joseph Stalin, NKVD agent Iosif Grigulevich orchestrates an unsuccessful assassination attempt on exiled Russian revolutionary Leon Trotsky in Coyoacán, Mexico.^[†]

The Union of Soviet Socialist Republics (USSR), commonly referred to as the Soviet Union or Russia, was a transcontinental country that spanned much of Eurasia from 1922 until it dissolved in 1991. During its existence, it was the largest country by area, extending across eleven time zones and sharing borders with twelve countries, and the third-most populous country. An overall successor to the Russian Empire, it was nominally organized as a federal union of national republics, the largest and most populous of which was the Russian SFSR. In practice, its government and economy were highly centralized. As a one-party state governed by the Communist Party of the Soviet Union (CPSU), it was the flagship communist state. Its capital and largest city was Moscow.