Police have discovered an "enormous" cannabis farm in an underground nuclear bunker.
Police carried out a midnight raid on RGHQ Chilmark, an underground bunker constructed in the 1980s in Wiltshire to house and protect government officials and dignitaries in the event of a nuclear attack.
The site is no longer owned by the Ministry of Defence but the bunker is still intact and the nuclear blast doors are in place.
Wiltshire Police attended the site after gathering intelligence.
A spokesman said officers knew the bunker was "almost completely impenetrable" so they waited outside for three people to leave.
The three men, aged 27, 30 and 45, from Somerset, were detained and officers used their keys to enter the bunker, where they found three more males, aged 15, 19 and 37, all of no fixed address, believed to be working as gardeners.
They discovered several thousand cannabis plants at various stages of growth, worth more than £1 million.
Detective Inspector Paul Franklin said: "There are approximately 20 rooms in the building, split over two floors, each 200ft long and 70ft wide.
"Almost every single room had been converted for the wholesale production of cannabis plants, and there was a large amount of evidence of previous crops. This was an enormous set-up.
"At this early stage of the investigation it is almost impossible to work out how many plants are inside, but we are talking thousands rather than hundreds, and we would estimate the value of the crop at over £1 million.
"I am convinced it is one of the largest crops ever discovered in Wiltshire.
"The actions of officers last night took a large amount of planning and teamwork, and I am very pleased that it has been so successful.
"This is the largest and most sophisticated cannabis factory I've ever experienced and I am delighted that we have been able to take such a large amount of illicit drugs off the streets of Wiltshire before they are able to reach vulnerable people within our communities."
The three men found in the bunker were arrested on suspicion of cannabis production and taken to custody in Melksham.
The three men detained outside the bunker were arrested on suspicion of cannabis production and human trafficking.