A team of Royal Navy bomb disposal experts from HM Naval Base Clyde were called to act after a vessel found a suspected mine in the waters around the Firth of Clyde on Tuesday.
The Northern Diving Group (NDG) was called after the Maritime and Coastguard Agency was alerted to the situation.
Following examination, the item, described as being in “pristine” condition, was confirmed to be a bomb.
“Considering it had been in the water for around 80 years, its condition was remarkable,” Lieutenant Commander Mark Shaw, Commanding Officer of NDG, said.
The Second World War German submarine-laid moored influence mine still contained 350kg of explosives, the Royal Navy said.
On Wednesday, the NDG team coordinated the lowering of the ordnance to the seabed and carried out a controlled explosion to dispose of the device.
Lt Cdr Shaw said: "This highlights the remaining presence of historic ordnance.
"Even small items can be unstable and present an explosive hazard; carrying-out a controlled explosion is the only safe way of dealing with them and neutralising the hazard."
He added that the NDG is "approaching 100 call-outs this year" supporting civil authorities with "all types of Explosive Ordnance Disposal".
The Commanding Officer of the NDG also urged anyone who may come across “a suspected piece of ordnance” not to interfere with it and “immediately contact the emergency services”.
The Northern Diving Group is one of two Fleet Diving Squadron area diving groups whose mission is to provide diving, Explosive Ordnance Disposal, and in-water maintenance and repair to the fleet.
Based at HM Naval Base Clyde, NDG comprises more than 40 Royal Navy clearance divers and support staff.
The team covers a vast area that was exposed to many bombing raids during the Second World War, from the highwater mark in Liverpool, stretching 12 nautical miles out to sea, encompassing Hull, Northern Ireland, the Scottish Western Isles, Shetland, and the Orkneys.