The UK Ministry of Defence (MoD) has reportedly requested maritime patrol aircraft (MPA) from the US military, as it attempts to track a suspected Russian submarine off the coast of Scotland.
The Independent reported that the presence of the Russian submarine is connected with the departure of one of the Royal Navy's Vanguard missile submarines from the west coast of Scotland. Vanguard vessels carry the UK's Trident nuclear deterrent.
Maritime patrol aircraft were recently deployed from Canada, France and the US.
As part of the move, two US Navy P3 Orion aeroplanes have been deployed to conduct anti-submarine patrols in the North Atlantic Ocean and a Royal Navy anti-submarine frigate has been dispatched in search of the vessel.
The UK scrapped its Nimrod patrol aircraft fleet in 2010.
The UK MoD said: "We have always been clear that tough decisions had to be taken in order to rebalance the defence budget, which included removing the Nimrod MR2 from service.
"However, maritime surveillance is provided through a combination of layered capabilities including surface ships, submarines and air assets such as the RAF Hercules, which searched for the missing yacht Cheeki Rafiki in May.
"The UK continues to work closely with its Nato allies in the operation of maritime patrol aircraft."
Reports have also suggested 'visits' by Russian submarines 'happening quite often' along the north and west coasts of Scotland.