On July 20th 1944, Claus von Stauffenberg and other conspirators attempted to assassinate Adolf Hitler, Führer of Nazi Germany, inside his Wolf's Lair field headquarters near Rastenburg, East Prussia. The name Operation Valkyrie—originally referring to part of the conspiracy—has become associated with the entire event.
On July 20th 1969, NASA's Apollo 11 Lunar Module lands 238,855 miles from Earth in the Sea of Tranquility and six hours later astronaut Neil Armstrong
exits the vehicle, descends a short ladder, and becomes the first human to walk on the moon. Minutes later, astronaut Buzz Aldrin will join Armstrong on the surface. Millions back home tune in to the historic event.
On July 20th 1976, Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. On July 20, 1976, it became the second spacecraft to soft-land on Mars, and the first soft lander to successfully perform its mission. Viking 1 held the record for the longest Mars surface mission of 2307 days or 2245 Martian solar days, until that record was broken by Opportunity on May 19, 2010.