Unexploded ordnance was apparently discovered by a vessel round the corner from Hill Head Harbour on Saturday, with Hill Head Coastguard being called to investigate.
After confirming what the incident was, the Royal Navy crew was called in to deal with the ordnance safely.
A spokeswoman from the UK Coastguard said: '˜It was a vessel that was just doing a survey of the surrounding area who found the bomb and reported it.
'˜A diving team of four went out in a rib and found the ordnance at around 12.18pm on Saturday.
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'˜It was non-explosive and so they took it back to shore with them.
'˜The ordnance itself was quite far out but it was still in the vicinity of the Hill Head Coastguard crew.'
Exact details of where the bomb came from and how old it is are currently unknown.