Guernsey Police carried out a controlled explosion of a World War II mortar at L'Ancresse Bay on Tuesday.
A member of the public found the mortar just under the surface of the sand while out walking their dog.
The police were alerted and four officers carried out a controlled explosion at about 1730 GMT.
The device turned out to be a 50mm (2in) German mortar shell fired during World War II.
Officers said it may have originally been fired from the nearby emplacement on Chouet headland, which had a belt-fed mortar launcher.