An American think tank says that without U.S. assistance, South Korea in 1974 would have fallen to a North Korean invasion in just 216 days.

The Nautilus Institute on Friday said an 800-page classified report concluded that American nuclear missiles and artillery battalions stationed in South Korea could also have been used to deter the North in 1975.

Written by the now-defunct U.S. Army Pacific Command, the report said then U.S. Defense Secretary James Schlesinger urged the use of nuclear weapons on the Korean Peninsula in his strategy.