The date was May 23, 1967, and the United States and Soviet Union were facing off at the heigh of the Cold War. The U.S. Air Force thought their surveillance radars were being jammed by the Soviets, but military space-weather forecasters set them straight: it was actually a huge eruption on the surface of the sun that was disrupting communications.

That’s a good thing: the Air Force was preparing for war against the Soviets, and things could have gotten ugly very, very fast had the U.S. military not realized that the sun was the culprit, according to a statement by the American Geophysical Union about a new study about that momemnt in history.

It all started a few days earlier, when researchers saw a big group of sunspots on the solar disks. They sent huge flares blasting super-charged particles toward Earth, knocking out radio transmissions and satellite communications. On that day, all three of the Air Force’s Ballistic Missile Early Warning System radar sites in Alaska, Greenland and the United Kingdom looked like they were being jammed.

The Air Force thought the Soviet Union was behind it, and since radar jamming is an act of war, commanders began to prepare aircraft armed with nuclear weapon. That alone wouldn’t necessarily be enough to start nuclear war — they were put in the air as “additional forces” rather than the first line of attack — but it certainly would have dramatically raised the prospect if the Soviets responded in kind.

Fortunately, however, the planes never launched, as forecasters with the North American Aerospace Defense Command (NORAD) determined that the sun flare was the cause, and not the Soviets. Crisis averted.

“The geomagnetic storm, which began about 40 hours after the solar flare and radio bursts, went on to disrupt U.S. radio communications in almost every conceivable way for almost a week, according to the new study. It was so strong that the Northern Lights, usually only seen in or near the Arctic Circle, were visible as far south as New Mexico,” the statement reads. “It was the military’s correct diagnosis of the solar storm that prevented the event from becoming a disaster. Ultimately, the storm led the military to recognize space weather as an operational concern and build a stronger space weather forecasting system.”