Key point: There is evidence that the United States put its nuclear forces in the region on alert during the EC-121 crisis.

April 15, 1969 marked one of the deadliest days for the United States in postwar Asia. The shootdown of a U.S. Air Force reconnaissance aircraft off the coast of North Korea was unprovoked, and cost the lives of thirty-one Americans. Despite stern calls from Congress to avenge the deaths of the American servicemen, President Richard M. Nixon ultimately decided to avoid retaliation, lest he start a second Korean War. Although Nixon never acted on them, he had a range of military options should his administration have decided to strike.

On the morning of April 15, a U.S. Navy WV-2, the Navy version of the EC-121M “Warning Star” aircraft and a precursor to today’s E-3 Sentry AWACS, took off from Atsugi, Japan bound for coast of North Korea. The aircraft, call sign “Deep Sea 129.” The EC-121M flew in a clockwise ellipse over the Sea of Japan, collecting North Korean signals intelligence for analysis later. North Korean troops had conducted numerous cross-border raids and shootings against South Korean and American troops, and U.S. forces needed to know ahead of time if North Korea was planning a surprise attack.

Five and a half hours into the mission, U.S. radars in Korea detected two North Korean People’s Air Force MiG-17 “Fresco” fighters taking off from their airbase. After losing them on radar, U.S. forces reacquired them and realized they were on an intercept course against Deep Sea 129. The converted American civilian transport, with thirty-one Navy and Marine Corps personnel on board, disappeared from radar shortly afterward. Soviet and American warships sent into the area to assist with the search would turn up two bodies and pieces of aircraft debris.

The reaction from Congress was fierce. “There can be only one answer for America: retaliation, retaliation, retaliation!” thundered the chairman of the House Armed Services Committee, Rep. L. Mendel Rivers. Rivers demanded “whatever is necessary. If nuclear weapons are required, let them have it. It’s time to give them what they ask for.” A number of tough military options of varying severity were drawn up by the Pentagon and presented to the president and his National Security Council.

One of the options available to the White House was to attack military airfields in North Korea, with the goal of disrupting “Pyongyang’s military posture and impose a penalty on the North Korean leadership for shooting down the U.S. aircraft.” Four aircraft carriers, Enterprise, Kitty Hawk, Ranger and Hornet, were available with forty-eight to seventy-two hours’ advance warning, as well as tactical aircraft from Okinawa, mainland Japan, South Korea and Guam. Among the many air-strike proposals, Wonsan Air Base was a consistent target, suggesting that the MiGs that shot down Deep Sea 129 were based there.

Another retaliatory option, code-named Fractured Pine, involved U.S. Navy cruisers armed with Talos surface-to-air missiles. Two cruisers would take up positions off the coast of North Korea within the vicinity of Wonsan and Sodong-Ni military airfields, and shoot down any North Korean aircraft taking off from them. The Talos had, in the past, been used to shoot down North Vietnamese aircraft, with six missiles claiming two of Hanoi’s fighters. The cruisers, along with their escorting destroyers, would close with the North Korean coastline at night and prepare to shoot down any fighters taking off from the bases in the early morning hours. Although the option was considered low risk, planners assessed it would cause North Korea to retaliate in unpredictable ways.

One of the most striking military options was the use of B-52 bombers in a retaliatory strike against North Korean military targets. Twelve to twenty-four B-52 bombers based at Guam and typically directed against North Vietnamese targets would fly a low-level nighttime mission against targets in North Korea. Each would carry 108 bombs, presumably five-hundred-pound Mk. 82 conventional high-explosive bombs. The bombers would be refueled by tankers based on Okinawa, and would take six hours to reach their target. The paper noted that the presence of B-52 bombers near the Soviet border might cause an “adverse reaction.”

Finally, there is evidence that the United States put its nuclear forces in the region on alert during the EC-121 crisis. After the USS Pueblo incident, the U.S. military had put together a nuclear contingency plan, code-named Freedom Drop, for the use of tactical nuclear weapons against North Korea. As part of the Standard Integrated Operating Procedure, or SIOP, the U.S. Air Force based F-4D Phantom II fighters armed with B61 nuclear bombs at Kunsan Air Base, South Korea. Four F-4Ds were on alert twenty-four hours a day in order to strike targets in North Korea as part of a wider nuclear conflict. According to a report on NPR, one pilot on duty at Kunsan during the crisis recounted that he was told to “prepare to strike my target,” which was an airfield in North Korea. The pilot stayed with his airplane for several hours until told to stand down. While his orders were likely strictly precautionary, the incident illustrates how crises rippled through America’s vast nuclear network.

Ultimately, the Nixon administration—not dovish by any stretch of the imagination—declined to retaliate. The administration’s dilemma was summarized in a paper prepared for the National Security Council: “The more serious the U.S. action, the greater is the risk of North Korean counteraction and escalation.” With the Cold War raging and the Vietnam War already ongoing, the United States could ill afford a new war in Asia.

Instead, Nixon decided to continue U.S. reconnaissance flights in the region while providing them with military escorts to prevent another downing. This showed American resolve against the attack while still continuing the intelligence collection mission. It also had the benefit of not escalating what was already a crisis. Nixon’s response to the cowardly, unprovoked attack that cost thirty-one American lives was a model for crisis management and escalation avoidance.

Kyle Mizokami is a defense and national-security writer based in San Francisco who has appeared in the Diplomat, Foreign Policy, War is Boring and the Daily Beast. In 2009 he cofounded the defense and security blog Japan Security Watch. You can follow him on Twitter: @KyleMizokami. This first appeared in 2018.

Image: Reuters.