U.S. Air Force fighter pilots put on quite the show in the Welsh countryside this week.

A group of F-15E Strike Eagles out of RAF Lakenheath in Suffolk, England, were caught on camera twisting and turning through the mountains near the town of Dolgellau at altitudes as low as 500 feet, WalesOnline reported. Pilots learn to use the terrain to help avoid being tracked by radar, a sometimes crucial skill in a combat zone.

The Mach Loop is a quiet, one-way route often used by NATO countries for low-level flight training. In this case, the Air Force pilots were so low that hillside onlookers could see directly into the cockpits.

The Royal Air Force is known to use the loop in training, and the Red Arrows aerobatic display team has practiced there in the past.

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