The bomb squad was dispatched to Sidmouth after a woman clearing out her late father’s garage found a hand grenade.
Police attended the scene in Summerfield at 12.30pm on Wednesday and identified the item as a No 5 Mills grenade.
Officers put a cordon in place to protect the public.
The bomb disposal team made the device safe, X-rayed it and took it away to be destroyed in a controlled explosion.
PC Steve Lee, of Sidmouth’s neighbourhood policing team, described the grenade as a ‘viable device’ that ‘could have gone bang’.
He told the Herald: “Police would like to remind members of the public who are clearing out properties of older relatives to be aware of any military items they may find - particularly ordinance - and report such finds by calling 999.
“On no account should they handle or touch these items, as they may be live and potentially unstable.”
The Mills bomb was adopted by the British Army as its standard hand grenade in 1915 and it saw widespread use in World War One.
The original variant had a seven-second fuse.
A spokeswoman for the Royal Navy said: “We find these grenades quite often.
“This should be a warning to people who keep these things as memorabilia. Nine times out of 10 they are going to be safe, but you don’t know what can happen when you’re dealing with ordinance. The best thing to do if you find an explosive device is to call the police and they can contact the bomb squad.”
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