Police seized a haul of military weapons, including grenade launchers and an SA 80 rifle, in a raid on a house in County Durham.
Officers found 16 weapons, together with ammunition, component parts and manuals, in the search at Chatsworth Terrace, Darlington, on Wednesday.
Army investigators, probing the sale of suspected stolen weapons on the internet, requested the raid.
A 40-year-old man was arrested and released on police bail.
Det Con Angela Makepeace, of Durham Police, said the suspect lived alone at the home and was known to have had an interest in military equipment for several years.
She said: "The weapons are being transferred to the police armoury in Durham, where they will be examined in detail.
"There are 16 weapons in total, including grenade launchers, an SA80 rifle, a replica sniper's rifle, as well as a wide range of component parts and a wide range of ammunition."