April 4

801 – During the Reconquista, Louis the Pious, son of Charlemagne and King of the Franks, recaptures Barcelona from the Moors after a siege lasting several months.

1581 – Francis Drake is knighted by Queen Elizabeth I for completing a circumnavigation of Earth.

1818 – The U.S. Congress, affirming the Second Continental Congress, adopts the redesign of the flag of the United States to reduce the flag to 13 red and white stripes to honor the original colonies and one star for each state.

1841 – President William Henry Harrison dies of pneumonia, becoming the first to die in office, and setting the record for the briefest administration, 31 days after inauguration.

1865 – A day after Union forces capture Richmond, Virginia, President Lincoln visits the Confederate capital.

1887 – Argonia, Kansas elects Susanna M. Salter as the first female mayor in the United States.

1933 – U.S. Navy dirigible airship USS Akron is wrecked off the New Jersey coast due to severe weather, resulting in the loss of 73 or the 76 aircrew aboard including Rear Admiral William A. Moffett MH, known as the architect of naval aviation.

1945 – American troops of the 4th Armored and 89th Infantry Divisions liberate the Ohrdruf, Germany concentration camp, while troops of the 80th Infantry Division capture Kassel northeast of Frankfurt am Main.

1949 –  12 nations sign the North Atlantic Treaty creating NATO, the North Atlantic Treaty Organization.

1968 – Martin Luther King Jr. is assassinated by James Earl Ray at the Lorraine motel in Memphis, Tennessee.

1969 – At St. Luke’s Episcopal Hospital in Houston, Texas, with no transplantable heart available, Dr. Denton Cooley implants the first temporary artificial heart in patient Haskell Karp, who lives for 65 hours.

1973 – The Twin Towers of the World Trade Center in New York City are officially dedicated.
A USAF Lockheed C-141 Starlifter, dubbed the Hanoi Taxi, makes the last flight of Operation Homecoming, returning U.S. Prisoners of War from Vietnam.

1975 – A USAF Lockheed C-5A Galaxy making the first flight of orphans during Operation Babylift, crashes on approach during an emergency landing at Tan Son Nhut Air Base, South Vietnam killing 138 of the 314 passengers and crew aboard.
Microsoft is founded as a partnership between Bill Gates and Paul Allen in Albuquerque, New Mexico.

1977 – Southern Airways Flight 242, a Douglas DC-9, crashes during a forced landing on a highway in New Hope, Paulding County, Georgia, killing 63 of the 85 passengers and crew aboard and 9 more on the ground.

1983 – Space Shuttle Challenger is launched on STS-6, its maiden voyage, from Launch Complex 39A at the Kennedy Space Center in Florida.

1984 – President Ronald Reagan calls for an international ban on chemical weapons.

1988 – Governor Evan Mecham of Arizona is convicted in his impeachment trial and removed from office.

1991 – Senator John Heinz of Pennsylvania and 6 others are killed when a helicopter collides with their airplane over an elementary school in Merion, Pennsylvania.

1994 – Marc Andreessen and Jim Clark found Netscape Communications Corporation under the name Mosaic Communications Corporation.

1996 – Comet Hyakutake is imaged by the USA Asteroid Orbiter Near Earth Asteroid Rendezvous.

2010 – A magnitude 7.2 earthquake hits south of the Mexico-USA border in Baja California, killing 2 people and damaging buildings on both sides of the border.