What happened 21 May in United States of America

21 May 1946: While conducting further impromptu experiments on the third plutonium core at Los Alamos National Laboratory, physicist Louis Slotin received a lethal dose of radiation. He died on 30 May 1946.

On May 21, 1962, Armstrong was involved in the "Nellis Affair". He was sent in an F-104 to inspect Delamar Dry Lake in southern Nevada, again for emergency landings. He misjudged his altitude, and did not realize that the landing gear had not fully extended. As he touched down, the landing gear began to retract; Armstrong applied full power to abort the landing, but the ventral fin and landing gear door struck the ground, damaging the radio and releasing hydraulic fluid. Without radio communication, Armstrong flew south to Nellis Air Force Base, past the control tower, and waggled his wings, the signal for a no-radio approach. The loss of hydraulic fluid caused the tailhook to release, and upon landing, he caught the arresting wire attached to an anchor chain, and dragged the chain along the runway.

On May 21, at Judgment Day, The Rock faced Triple H in an Iron Man match with Shawn Michaels as the special guest referee. With the score tied at five falls each, and with seconds left on the time limit, The Rock was disqualified when The Undertaker attacked Triple H, thus giving Triple H the 6–5 win and the title.

On May 21, 2009, it was announced that Ursula Burns would succeed Anne Mulcahy as CEO of Xerox. On July 1, 2009, Burns became the first African American woman to head a company the size of Xerox.

On 21 May 2019, on Einthoven's 159th birthday, he was honored with a Google Doodle.