A team of Royal Navy divers from HMNB Devonport disposed of a live grenade and a World War Two shell in two separate call-outs.
The team first responded to a grenade found at the Cornwall Energy Centre in St Austell, confirmed to be a live British military grenade, on Wednesday.
It was then urgently sent to Plymstock in Plymouth, following a report of an artillery shell found under a shed in a residential property.
After assessment, both items were safely removed for disposal, according to HM Naval Base Devonport.