Documents show the FBI created a “Plan C” during the Cold War, which could have been triggered in the event the US underwent a nuclear attack. It included putting the nation under martial law, rounding up “subversives,” and interning enemy diplomats.

The documents, acquired by transparency journalism organization MuckRock, detail the FBI plan created in 1956, which was shared with several top officials from every governmental department. The FBI also distributed papers regarding the plan to its field offices. The plan would have gone into effect “after a war has begun in which the US is involved or may become involved and prior to an actual attack on the US itself,” according to the documents.

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Under Plan C, martial law would be declared and the FBI would enact its ‘Emergency Detention Program,’ which entailed apprehending individuals whose affiliations with subversive organizations “are so pronounced that their continued liberty in the event of a national emergency would present a serious threat to the internal security of the country.” The document shows that as of April 1956, almost 13,000 people “were scheduled for apprehension in an emergency.”

FBI's Cold War 'Plan C' Prepared For Nuclear Attack, Including Martial Law: Documents http://t.co/am9XRphMif — PW Dorling (@Ausflatfish) January 30, 2015

Government organizations would decide which of their employees were essential and have them hide out in backup offices. Soviet embassies, meanwhile, would be searched for weapons, radios, and explosives.

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The documents also detail the ‘Internment of Enemy Diplomats,’ showing that the president would instruct enemy diplomats to be taken into protective custody, with the FBI assisting the Department of State.

“Soviet Block personnel who would be involved number about 500 persons in Washington, DC, and about 400 in New York,” the documents read. Enemy diplomats would be taken to detention hotels and held there by Immigration and Customs Enforcement under the state’s direction.

In case of nuclear war there was only Plan C. @MuckRock uncovers Cold War history via FOIA response from the FBI. http://t.co/1jUsZf1bGp — Laura Moorhead (@Laura_Moorhead) January 27, 2015

Despite the title of Plan C, one memo shows there was no Plan A or Plan B, but there was a Plan D that involved the relocation of the government up to or prior to a nuclear attack against the country.

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FBI workers were allowed tell their families about Plan C in vague terms only, but they were encouraged to make preparations. "The stressing to all employees that it is the employee's moral responsibility to plan for survival and for the care of his family, to see that his family is aware of such planning, and to go into such planning, in detail, with his family," one memo reads.

The plan was ordered to be destroyed in July 1957.

MuckRock has requested about 150 additional pages regarding Plan C under the Freedom of Information Act. The FBI is consulting with other agencies before releasing the documents.