In the late 1950s, research branches of the U.S. military began monitoring solar activity and space weather, the disturbances in Earth’s magnetic field and upper atmosphere that can interfere with radio transmissions, power lines and other technologies. By the ‘60s, a special branch of the U.S. Air Force’s Air Weather Service (AWS) was dedicated to monitoring the sun and watching out for the brief but powerful eruptions of radiation from the sun’s surface known as solar flares. A network of observers in the United States and abroad reported any activity to the North American Aerospace Defense Command (NORAD), a joint U.S.-Canadian organization charged with defending and controlling North American airspace.
These observation and forecasting operations seem to have paid off—big time—on May 23, 1967, when a powerful solar storm disrupted three Ballistic Missile Early Warning System (BMEWS) sites in the far Northern Hemisphere, used by the U.S. military to detect incoming Soviet missiles. During this period of the Cold War, the U.S. Air Force flew continuous alert aircraft armed with nuclear weapons, but the suspicion that the Soviet Union had tampered with its radar surveillance operations—considered an act of war—led commanders to put additional nuclear-equipped forces in a “ready to launch” status.
But the planes stayed on the ground, and nuclear war didn’t break out. Now, retired U.S. Air Force personnel have described what happened publicly for the first time in a new study accepted for publication in Space Weather, a journal of the American Geophysical Union (AGU). Contributing authors of the study include experts from the University of Colorado, Boulder, the National Oceanic and Atmospheric Administration (NOAA), Baylor University and Boston College.
As the new study reveals, researchers noticed a large group of sunspots—the dark, relatively cool areas on the sun’s surface that can produce solar flares—with particularly strong magnetic field in one area of the sun on May 18, 1967. (Strong solar flares can also be accompanied by eruptions of solar plasma called coronal mass ejections, or CMEs. These can cause even more damage, sparking geomagnetic storms that can jam power grids, among other technologies.)
On May 23, a solar radio observatory in Massachusetts reported the sun was emitting high levels of radio waves, while observatories in New Mexico and Colorado recorded a solar flare that was visible to the naked eye. NORAD’s Solar Forecast Center in Colorado Springs put out a bulletin announcing that a significant worldwide geomagnetic storm was forecast to occur within 36-48 hours. That same day, the three BMEWS sites in Alaska, Greenland and the United Kingdom all appeared to be jammed, causing the Air Force to go on high alert.
According to the study, the incident was “a near trip-wire in the tense political and military landscape of the time.” If the nuclear-armed planes had taken off, the study said, it would have been very different to communicate with them due to interference from the solar storm. Such a launch would have been “very provocative,” risking a Soviet counter-attack and all-out global war.
