On May 15: Independence Day observed in Paraguay (1811).
- 1602 - Bartholomew Gosnold became the first European to discover Cape Cod.
- 1756 - England declared war on France, starting the Seven Years' War.
- 1911 - The U.S. Supreme Court declared Standard Oil an "unreasonable" monopoly.
- 1932 - May 15 incident (go ichi go jiken): Japan's prime minister Inukai Tsuyoshi was assassinated by young naval officers in Tokyo.
- 1957 - Britain tested its first hydrogen bomb in Operation Grapple.
- 1970 - The Beatles' last LP, Let It Be, was released.