From here

"In 1971, a team of scientists who were experts in the use of atomic clocks set out to detect and measure time dilation and other relativistic effects. The research team was able to devise a cheap and effective plan, which received some support from the Office of Naval Research. We are told that the researchers purchased three around-the-world tickets on regularly scheduled commercial airliners-two tickets for the accompanying scientists and one for an array of four atomic clocks. The clock array had its own seat; it sat, belted in for safety, between its two caretakers. Before leaving on the trip, the clocks were synchronized with a master clock at the U.S. Naval Observatory. The four clocks then went around the world, following which they were compared again with their counterpart, which had stayed behind at the Naval Observatory. After correcting for the rotation of the earth and the variation of the force of gravity with altitude, it was found that the clocks that had been in motion in their journey around the earth had in fact slowed as compared with the clock at the Naval Observatory, and by exactly the amount predicted by the theory of relativity. The result was further confirmed in a second around-the-world flight in the opposite direction. "

just the first one i found on google