Who was the first American astronaut?

On the anniversary of Alan Shepard's historic 'Freedom 7' flight in 1961, LIFE features photos from that remarkable era. (Above: Shepard, c., with fellow astronauts Deke Slayton and Gus Grissom, after his flight.)

When Soviet cosmonaut Yuri Gagarin became the first man in space in April 1961, a stunned America had two questions: How could this happen? and When is one of our guys going up there? Weeks later, on May 5, 1961, the second question was emphatically answered when 37-year-old Alan Shepard blasted off from Cape Canaveral on his own historic flight — a feat that made the New Hampshire native the first American in space and marked a major United States triumph in the Space Race.

Here, on the anniversary of Shepard’s historic flight, LIFE.com presents pictures, the vast majority of them by LIFE’s Ralph Morse (dubbed “the 8th Mercury astronaut” by John Glenn), along with Morse’s own memories of that amazing era, and those magnificent young men in their flying machines.

Of the three astronauts chosen as candidates for America’s first manned space flight, only one could or would ultimately star in what LIFE magazine, in March 1961, called the “violent, historic event. . . . Some time this spring, either John Glenn or Virgil Grissom or Alan Shepard will crawl into a small capsule on top of a Redstone rocket and wait for the most awesome journey that man has ever taken.”