On April 13

War in Afghanistan: In an airstrike in Nangarhar Province, the U.S. military dropped the most powerful conventional bomb used in combat.

The board of Rosendale, New York, voted 3–2 to approve the purchase of Joppenbergh Mountain.

Andrew Hussie's webcomic Homestuck debuted, and later concluded on the same day in 2016.

Twenty-three people died in a fire at a homeless hostel in Kamień Pomorski; it was Poland's deadliest fire since 1980.

In golf, 21-year-old Tiger Woods became the youngest player to win the Masters Tournament, breaking the record for the lowest four-round score.

An Israel Defense Forces helicopter fired rockets at an ambulance, killing two women and four children in Mansouri, Lebanon.

Forty people died in an explosion at an ammunition factory in Lapua, Finland.

Catch a Fire, the landmark reggae album by Bob Marley and the Wailers, was released.

In the midst of the Cold War, American pianist Van Cliburn won the inaugural International Tchaikovsky Competition in Moscow.

The Vietnamese National Army captured Ba Cụt, a military commander of the religious sect Hòa Hảo, which ran a de facto state in South Vietnam in opposition to Prime Minister Ngô Đình Diệm.

The CIA began Project MKUltra, an illegal, covert human research program into mind control.

Ian Fleming's novel Casino Royale was published as the first work to feature the British spy character James Bond.

Nakam, a Jewish organization seeking revenge for the Holocaust, attempted to poison thousands of SS prisoners at Langwasser internment camp, but did not kill anyone.

World War II: German news announced the discovery of a mass grave of Polish prisoners of war killed by Soviet forces in Katyn, Russia, causing a diplomatic rift between the Polish government-in-exile and the Soviet Union.

The Neoclassical Jefferson Memorial (pictured) in Washington, D.C., was formally dedicated on the 200th anniversary of Thomas Jefferson's birth.

Austrian soldier Anton Schmid was executed for rescuing Jews from the Ponary massacre in Vilnius.

C. Rajagopalachari led the non-violent Vedaranyam March from Trichinopoly towards Vedaranyam.

The Roman Catholic Relief Act received royal assent, removing the most substantial restrictions on Catholics in the United Kingdom.

American Revolutionary War: British and Hessian forces conducted a surprise attack against a Continental Army outpost at Bound Brook, New Jersey.

The first performance of the oratorio Messiah by George Frideric Handel (pictured) took place in Dublin.