Mercury-Atlas 4 launched 1961

Mercury insignia

NASA launched the unmanned spacecraft Mercury-Atlas 4, September 13, 1961.  After two failed launches, one partial success and only one other complete success, Mercury-Atlas 4 completed all flight objectives successfully.  It orbited the Earth once and splashed down in the Atlantic Ocean less than two hours after launch.

Mercury-Redstone 4 launched 1961

Virgil 'Gus' Grissom was launched aboard Liberty Bell 7, a Mercury-Redstone 4 vehicle July 21, 1961, the second US spaceflight.  His flight lasted only 15 minutes and 30 seconds and reached an altitude of over 102 nautical miles. 

The Liberty Bell 7 had a new explosive hatch release to allow an astronaut to escape the spacecraft in the event of an emergency.  Grissom's flight went successfully until just after splashdown when the hatch accidentally blew, threatening to drown Grissom.  Fortunately, he was rescued safely but the capsule sank into the Atlantic Ocean.  It was recovered in 1999.