Neil Armstrong and Buzz Aldrin were chosen to be the first to walk upon the Moon almost by accident. It could have been any one of twenty men.

Neil Armstrong believed the chances of a successful touchdown were 50/50

Several years before, the Apollo astronauts were all assembled for one of the first briefings. The head of the astronaut selection office, Alan Shephard - himself destined to walk upon the Moon - said that he did not know who would be the first to set foot on the lunar surface.

But, he said, he did know that that man was sitting in the room with him, as well as the second and the third.

In a roster of crew assignments before the date of the landing was decided, Armstrong and Aldrin were given Apollo 11.

Depending upon the success of preceding mission it may or may not have been designated as the first landing.

By the time Apollo 8 had reached the moon at Christmas 1968 it seemed likely that Apollo 11 would attempt the first landing.

Armstrong believed the chances of a successful touchdown were only 50/50. Before launch, during a dinner with the head of the American space agency Nasa, the crew of Apollo 11 was given a unique promise.

Nasa's head, Tom Paine, said to them that if they failed to land on this mission, then the next mission would be theirs to try again. So it would be until they were successful.

Watched by millions, the mission begins

"The Eagle has wings"

The historic mission began on July 16th at 0932 local time. Watched by over two million people in the vicinity, the Saturn V rose into the air from pad 39a.

The journey to the Moon was quiet. It had been done twice before and was almost routine.

Eagle, the landing craft, separated from Columbia on the far side of the Moon.

Armstrong reported, "The Eagle has wings."

At the lowest point in its orbit, it fired its engine to begin the descent.

The landing was a drama. Several times during the descent alarms sounded: at 14,300 metres (47,000 feet) it seemed that the computer was being overloaded.

"You are go to continue powered descent," said capsule communicator Charlie Duke at mission control.

Aldrin saw the Earth out of his window as the Eagle turned for the final descent.

Another alarm. Armstrong: "Give me a reading on the program alarm." According to the computer, Eagle was coming in too fast. The mission book said abort.

But Steve Bales, the 26-year-old flight guidance officer, saw that it was just one reading, and that everything else was OK.

The Eagle then got a radar lock on the lunar surface that seemed to be normal. He signalled to Charlie Duke, who said, "You are go, you are go!"

They were at 6,400m (21,000 ft) and descending at 3,700m (12,000 ft) a minute. The landing, or an abort, was just moments away.

Looking out of the window Armstrong saw that they were heading for a field of boulders, in which landing was impossible. He took manual control and began skimming across the surface to find a better spot.

Charlie Duke then said, "30 seconds." The fuel was running out.

The Eagle has Landed

Then, seconds later, the metal feelers that protruded from Eagle's footpads touched the surface. Aldrin said the first words ever spoken by Man on another world; "Contact light."

It was 2118 BST, July 20th 1969. Man was on the Moon.

"The Eagle has landed"

No one who witnessed those translucent black and white images on the Sea of Tranquillity will forget them.

Here was man on another world, moving around in the ultimate desert, silent and stark, on a tiny world where the horizon was only one and a half miles away.

Back on Earth, someone placed a hand-written note next to the eternal flame on president Kennedy's grave.

It read "Mr President, the Eagle has landed."