| April 9, 1859 | April 9, 1959 |
| • A 23 year old Missouri youth named Samuel Clemens receives his steamboat pilot's license. He piloted his own boats until the Civil War halted steamboat traffic. He picked up the pen name "Mark Twain" from a boatman's call noting that the river was only two fathoms deep, the minimum depth for safe navigation. | • NASA introduces America's first astronauts to the press: Scott Carpenter, Gordon Cooper Jr., John Glenn Jr., Virgil "Gus" Grissom, Walter Schirra Jr., Alan Shepard Jr. and Donald Slayton. The seven men, all military test pilots, were carefully selected to take part in Project Mercury. America's first manned space program. |
| April 10, 1942 | April 10, 1951 |
| • The Baatan Death March begins in the Philippines as some 75,000 captured Filipino and American troops start a forced march to a Japanese prison camp. Hundreds of Americans and many more Filipinos would die during the six day trek, which was punctuated with atrocities committed by the Japanese guards. | • The USS Thresher, an atomic submarine, sinks in the Atlantic Ocean, killing its entire crew. One hundred and twenty nine sailors and civilians were lost when the the sub unexpectedly plunged to the sea floor 300 miles off the coast of New England. |
| April 11, 1945 | April 11, 1951 |
| • The American Third Army liberates the Buchenwald concentration camp, near Weimar, Germany. Among those saved by the Americans was Elie Wiesel, who would go on to win the Nobel Peace Prize in 1986. | • In perhaps the most famous civilian-military confrontation in U.S. history, President Harry Truman relieves General Douglas MacArthur of command of U.S. forces in Korea. The firing of MacArthur set off a brief uproar among the American public, but Truman remained committed to keeping the conflict in Korea a "limited war". |
| April 12, 1633 | April 12, 1861 |
| • The inquisition of physicist and astronomer Galileo Galilei for holding the heretical belief that the Earth revolves around the sun begins. Galileo agreed not to teach the heresy anymore and spent the rest of his life under house arrest. It took more than 300 years for the church to admit that Galileo was right and to clear his name of heresy. | • The American Civil War begins when Confederate shore batteries under Gen. P.G.T. Beauregard open fire on Union-held Fort Sumter in South Carolina's Charleston Bay. |
| April 13, 1970 | April 13, 1990 |
| • Disaster strikes 200,000 miles from Earth when oxygen tank No. 2 blows up on Apollo 13, the third manned lunar landing mission. Mission commander Lovell reported to mission control on Earth: "Houston, we've had a problem here". | • The Soviet government officially accepts blame for the Katyn Massacre of World War II, when nearly 5,000 Polish military officers were murdered and buried in mass graves in the Katyn Forest. The admission was part of Soviet leader Mikhail Gorbachev 's promise to be more candid concerning Soviet history. |
| April 14, 1865 | April 14, 1912 |
| • President Abraham Lincoln is shot in the head at Ford's Theatre in Washington, D.C. The assassin, John Wilkes Booth, shouted, "Sic Semper tyrannis! (Ever thus to tyrants!) The South is Avenged", as he jumped onto the stage and fled on horseback. | • Just before midnight in the North Atlantic, the RMS Titanic hits an iceberg, rupturing five watertight compartments along her starboard side. Hours later the massive vessel sank, and more than 1,500 people died in the icy North Atlantic waters. |
| April 15, 1924 | April 15, 1967 |
| • Rand McNally releases its first comprehensive road atlas. Today Rand McNally is the world's largest maker of atlases in print and electronic media. | • Massive parades to protest Vietnam policy are held in New York. Police estimated that 100,000 to 125,000 people listened to speeches by Martin Luther King Jr., Stokley Carmichael and Dr. Benjamin Spock. Prior to the march, nearly 200 draft cards were burned by young men in Central Park. |
| April 16, 1917 | April 16, 1947 |
| • Vladimir Lenin, leader of the revolutionary Bolshevik Party, returns after a decade of Exile to take the riens of the Russian Revolution. | • A massive explosion occurs during the loading of fertilizer onto the freighter Grandcamp at a pier in Texas City, Texas, killing 600 people. The blast was heard 150 miles away and was so powerful that the ship's anchor was found 2 miles away. |
| April 17, 1961 | April 17, 1964 |
| • About 1,500 CIA trained Cuban exiles launched the diastrous Bay of Pigs invasion of Cuba in a failed attempt to overthrow the government of Fidel Castro. | • Ford introduces the Mustang on the first day of the New York World's Fair in Flushing, Queens. The base price for the Ford Mustang was $2,368, but buyers purchased an average of $1,000 worth of options. |
| April 18, 1775 | April 18, 1942 |
| • Paul Revere began his famous ride from Charlestown to Lexington, Mass., warning American colonists that the British were coming. | • An air squadron from the USS Hornet led by Lt. Col. James H. Doolittle raided Tokyo and other Japanese cities. |
| April 19, 1993 | April 19, 1995 |
| • The 51 day siege at the Branch Dividian compound near Waco, Texas, ended as fire destroyed the structure after federal agents began smashing their way in; dozens of people, including leader David Koresh, were killed. | • Just after 9 a.m., a massive truck bomb explodes outside the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, collapsing the north face of the nine story building. The terrorist attack killed 168 people, including 19 children in the building's day care center. |
| April 20, 1902 | April 20, 1906 |
| • Scientists Marie, and Pierre Curie isolated the radioactive element radium. | • Firefighters halt the spread of flames in San Francisco after an earthquake two days earlier caused a substantial part of the city to burn. Nearly 700 people lost thier lives and 200,000 were left homeless. |
| April 21, 1649 | April 21, 1918 |
| • The Maryland Toleration Act, which provided for freedom of worship for all Christians, was passed by the Maryland Assembly. | • In the skies over France, Manfred von Richthofen, the notorious German flying ace known as the "The Red Baron", is killed by Allied fire. Richthofen downed 80 enemy aircraft before his death at age 25 and is regarded to this day as the ace of Aces. |