Plans for a nuclear submarine were donated to a charity shop.
They were found in the lining of a suitcase handed in anonymously at a Barnardo’s store.
The 6ft document shows details of £200million sub HMS Trafalgar.
It went into service during the Cold War, patrolling under the Arctic ice to hold off the USSR’s subs.
Stella Parker, who manages the shop in Porthmadog, north Wales, joked: “Someone said that if the phone rang and it was someone with a Russian accent, I should put it down.
“I can only imagine the family of someone who had passed away donated the suitcase not knowing the plan was there.”
Experts told Stella the plans were probably posted on the sub to familiarise the crew with its layout.
HMS Trafalgar was scrapped in 2009. The plans will be auctioned off.
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