Mr Keen said he has found more than half a dozen over the years and on this occasion he was diving for scallops near the bathing pools when he came across the mine.
‘The strange thing about this was that it was lying totally exposed on the sea bed and I’d never seen it before – it was just a bit further in from where I normally go,’ he said, adding that many divers must have swum past it.
The mine was partially corroded and did not contain its full payload of 870lb of explosives.
Previously Mr Keen has found similar mines in Soldiers Bay and near Moulin Huet.
He said they were all part of the same string of mines dropped by the British to prevent boats sailing from Guernsey and interfering with the Allied invasion of Normandy.
Designed to sit on the sea bed and detonate when disturbed by the sound of passing ships or submarines, Mr Keen said that a bomb disposal expert from the UK had told him that in the case of this string it looked like the mines had not been primed correctly before being dropped so they never became active.
Another unexploded device was also detonated at the weekend. Mr Keen said this was a depth charge that he had discovered several months ago.
Police bomb disposal team leader PC Stuart Allan said the charge was dealt with the day after the mine and while the Royal Navy team was available.
Mr Keen had taken video footage of the depth charge after he discovered it and this had been sent to the Navy team for them to assess prior to their visit.
PC Allan said the charge had most likely been moved by the current from the ‘ammo wreck’ which is just outside St Peter Port Harbour.
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