An investigation has been launched after "official sensitive" documents were reportedly found in the toilet of a pub.
The documents, about a £1.3 billion Royal Navy "hunter killer" submarine HMS Anson, were left in a cubicle in The Furness Railway in Barrow-in-Furness, The Sun newspapers says.
They showed the inner workings of the submarine and are used by submariners learning how to isolate and depressurise elements of its system.
The Royal Navy has said the papers were generic resources and did not contain any classified information.
A source told The Sun the pub was packed when the files, marked “official sensitive”, were discovered on the floor of a cubicle.
HMS Anson is an 'advanced nuclear-powered attack submarine', which was built at the BAE Systems shipyard in Cumbria, close to the Wetherspoons pub.
The 97m-long vessel is the fifth of the new Astute-class attack submarines to join the Royal Navy fleet.
They are capable of firing tomahawk missiles and described as the “largest, most advanced and most powerful attack submarines” ever used in the navy on its website.
A naval source said: "These documents enable submariners and contractors to understand how systems interact.
"They do not detail how they work, just that they exist."
They added that the files only contained simplistic designs of the systems on board, without revealing how they work.
A Royal Navy spokesman said: “These are generic training documents that carry no classified information.
"However, we take all security matters extremely seriously and will investigate the circumstances of their discovery.”
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