The BBC reported that a passenger ferry on the River Clyde was caught up in an international war exercise.
Operation Neptune Warrior, a training exercise for Nato warships, is taking place off the west coast of Scotland.
A threat by the U.S. Navy to fire on unidentified ships was transmitted to the Kilcreggan to Gourock ferry as it crossed a ship's path.
A spokesman for HM Naval Base Clyde said the ferry was in no danger and an investigation is under way.
The MV Kenilworth was making its regular 10-minute crossing at about 0940 BST on Monday when the incident happened.
The ship was leaving Faslane naval base for the two-week exercise.
It is understood it mistakenly broadcast a warning on VHF Channel 16, the international calling and distress frequency, instead of on an exercise frequency.