Special forces departed Plymouth under tight security after two Chinook helicopters took off from RM Bickleigh in darkness.
The helicopters were operated by 7 Squadron, part of the Joint Special Forces Aviation Wing based at RAF Odiham.
Officers from Devon and Cornwall Police blocked the road and restricted public movement while the helicopters took off.
Boats were loaded onto the helicopters before personnel were winched up from the Royal Marines base, home to 42 Commando.
It comes just weeks after green berets from the same base took part in the boarding of a Russian shadow fleet oil tanker in the English Channel during a major Royal Navy operation.
It is currently unknown whether the latest departure was linked to a military operation or training exercise.
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