Declassified documents released on Wednesday revealed the United States studied plans for a nuclear strike on North Korea in 1969, but backed down after then-president Richard Nixon decided it was best to remain calm. In 1969, North Korea shot down a U.S. spy aircraft over the Sea of Japan, killing the 31 personnel on board. The documents, released after requests under the Freedom of Information Act, show the government considered a number of options, including conventional and nuclear attacks. In one contingency plan named “Freedom Drop,” the United States would use nuclear weapons to destroy military command centres, airfields and naval bases in North Korea. Then-defence secretary Melvin Laird said civilian casualties “would range from approximately 100 to several thousand” in a classified memorandum to Nixon’s national security adviser Henry Kissinger. There is no indication that the government seriously considered a nuclear strike.