Over the past week, unidentified drones have been seen flying over joint U.S.-U.K. military bases in the United Kingdom.

Small, unmanned craft were seen flying over four bases in England, the U.S. Air Force in Europe said. The Pentagon said that there had not been “any significant mission impact.”

These latest drone sightings come after it was reported in The Wall Street Journal that mysterious drones swarmed the area around Langley Air Force Base, Virginia, in December 2023 for 17 days.