On April 21

The Indonesian Navy submarine Nanggala sank, resulting in the deaths of all 53 people on board.

The city of Flint, Michigan, U.S., changed its water source to the Flint River, which exposed residents to lead poisoning.

Ukraine and Russia signed the Kharkiv Pact, extending the Russian lease on naval facilities in Crimea.

South Vietnamese president Nguyễn Văn Thiệu resigned on hearing of the fall of Xuân Lộc, the last battle of the Vietnam War.

In response to a dispute over wheat production quotas, Leonard Casley declared his 75 km2 (29 sq mi) farm in Western Australia to be an independent country as the Hutt River Province.

A violent tornado strikes multiple schools and destroys houses in Belvidere, Illinois, United States, causing over 450 casualties.

The Century 21 Exposition, the first world's fair in the United States since World War II, opened in Seattle.

United Airlines Flight 736 collided with a U.S. Air Force fighter jet over southern Nevada, resulting in the deaths of all 49 people on board both aircraft.

The "Surgeon's Photograph", purportedly showing the Loch Ness Monster (later revealed to be a hoax), was published in the Daily Mail.

Forces of the Republic of Texas led by Sam Houston defeated the Mexican troops of General Antonio López de Santa Anna in the Battle of San Jacinto, the decisive and final battle of the Texas Revolution.

The Ladies of Trenton social club hosted a reception (depicted) for President-elect George Washington as he journeyed to New York City for his first inauguration.

J. S. Bach's cantata Bleib bei uns, denn es will Abend werden, was first performed on Easter Monday.

The Wignacourt Aqueduct (pictured) in Malta was inaugurated, and was used to carry water to Valletta for about 300 years.

Ælfric of Abingdon was appointed Archbishop of Canterbury

A debt was pardoned by the chief of Tondo on the island of Luzon and recorded on the Laguna Copperplate Inscription, the earliest known calendar-dated document found in the Philippines.