Bomb disposal teams were called after a Second World War sea mine was caught by a fishing boat.
The object became in stuck in the net of the vessel off the Devon coast at Brixham near Berry Head on on Saturday.
Brixham coastguard was alerted to the incident at 11am by a local fisherman who was unable to release the object from his boat.
The Royal Navy explosive disposal unit was called to the scene.
Teams lowered the object to the seabed and carried out a controlled explosion.
A spokesman for Brixham coastguard described the incident as "a rare one".