The bunker in Wiltshire used to be owned by the Ministry of Defence and was built in 1985 to protect government officials in the event of a nuclear war.
It stopped operating in 1992, and was sold in an auction in 1997.
Police said they waited outside the structure all night for three people to leave, and detained them, using their keys to gain entry into the otherwise impenetrable bunker.
They said almost all of the bunker's 20 rooms have been converted for growing cannabis.
