North Korea shot down a US plane in 1969, killing 31 Americans

— -- North Korea's recent threat to shoot down American military aircraft outside of its airspace recalls an infamous 1969 incident in which North Korean fighters shot down a U.S. Navy reconnaissance aircraft, killing the 31 American sailors aboard.

On April 15, 1969 two North Korean Mig-21 fighters shot down a U.S. Navy EC-121 reconnaissance aircraft over the Sea of Japan as it flew a regular surveillance mission in international airspace, 80 miles from the North Korean coast.

According to declassified documents, the unprovoked attack on the EC-121 aircraft led President Richard Nixon's national security team to draw up plans on how to deal with future North Korean provocations, including the use of nuclear weapons against the Asian nation.

According to a declassified National Security Agency (NSA) history of the shootdown, the EC-121 would normally have been staffed by a crew of 10 to 15 Navy personnel. But there were 31 individuals on the plane that day, as an equal number of trainees were aboard for the mission.

North Korea later claimed that the American plane was flying within its 12 mile territorial limit, but Nixon refuted that, using evidence gathered by the NSA.

In the crisis that followed, Nixon dispatched a number of aircraft carriers and other Navy ships to the Sea of Japan as a show of force.

Documents declassified in 2010 as part of a Freedom of Information Act request by the think tank National Security Archive show those plans included a wide range of options, including the use of tactical nuclear weapons to a full U.S. military response.