A British nuclear armed submarine spotted off the coast of Co Donegal was operating within maritime regulations, the Defence Forces has said.
Damien McCallig, the chief engineer on the RV Celtic Explorer, photographed the massive vessel on Thursday morning. He said it was passing 30kms northwest of Malin Head in Donegal.
Military sources said it appeared to be one of the Vanguard Class submarines operated by the Royal Navy. The vessels are nuclear powered and carry up to 16 Trident nuclear missiles, which each contain up to eight warheads.
The UK's four Vanguard submarines are based in Faslane in Scotland. It is likely the vessel spotted on Thursday was departing on patrol in the north Atlantic or returning to base.
Sightings of the submarines are extremely rare so close to Ireland, although it is understood the underwater route is frequently used by the Royal Navy.
It is not known why the operators of the vessel chose to surface so close to Donegal.
A Defence Forces spokesman said it could not comment on the operation of foreign military assets but that the submarine was operating outside Irish territorial waters and was compliant with the UN Convention on the Law Of the Sea (UNCLOS) rules for transit through International Waters.
“Territorial Waters are twelve Nautical Miles from the coast of Ireland. Under the UN Convention on the Law Of the Sea, there is no restriction on warships operating on the High Seas,” he said.
In 2004, a fire broke out on a Canadian submarine 150km off the coast of Donegal, just after it was purchased from the UK.
And in 2015, a British Astute Class submarine nearly crashed into a Donegal crab fishing boat.