A massive solar flare and the resulting geomagnetic storm that followed almost sparked World War III in 1967, it has been revealed. The US military at the time believed the Soviet Union was blocking its communication systems in the Polar Regions, and commanders put forces in a "ready to launch"status, thinking it was an act of war.

Conflict was, however, averted thanks to a solar monitoring system that had been set up just a decade earlier.

Using the Air Force's Air Weather Service (AWS), scientists saw a huge solar flare that emitted unprecedented levels of radio waves. From this, they predicted a worldwide geomagnetic storm would hit the planet within 36 to 48 hours later, causing serious disruption to radio and radar communications.

Details of this event have now been described – for the first time - in the American Geophysical Union's journal Space Weather. Delores Knipp, lead author of the paper, said: "Had it not been for the fact that we had invested very early on in solar and geomagnetic storm observations and forecasting, the impact [of the storm] likely would have been much greater. This was a lesson learned in how important it is to be prepared."

Data showed that on 18 May, 1967, an unusually large group of sunspots had appeared in a region of the sun. Five days later, researchers forecast a major solar flare was about to be produced. This was confirmed shortly after, with a flare visible to the naked eye appearing.

Retired Colonel Arnold L. Snyder, a solar forecaster who was working that day, said: "I specifically recall responding with excitement, 'Yes, half the sun has blown away,' and then related the event details in a calmer, more quantitative way."

The storm disrupted radars that had been designed to detect incoming Soviet missiles. Jamming these radars, or any type of attack on the stations they were held at, was considered an act of war. As a result, commanders put more forces in a ready to launch status. "This is a grave situation," Knipp said. "But here's where the story turns: things were going horribly wrong, and then something goes commendably right."

1967 Solar Storm NSO H-Alpha
The 1967 solar storm National Solar Observatory historical archive.

Experts from the Solar Forecast Centre at the North American Aerospace Defence Command were able to inform commanders about the geomagnetic storm just in time, telling them the Sun – not the Soviet Union – was to blame for the disruption. Military action was prevented and authorities recognised the importance of understanding space weather – leading to better and stronger forecasting systems being built.

Commenting on the study, Morris Cohen, an electrical engineer and radio scientist at Georgia Institute of Technology, said: "Oftentimes, the way things work is something catastrophic happens and then we say, 'we should do something so it doesn't happen again'. But in this case there was just enough preparation done just in time to avert a disastrous result."

x class
An X-class solar flare erupts on the left side of the sun on February 24, 2014. This composite image shows the sun in ultraviolet light with wavelengths of both 131 and 171 angstroms NASA/SDO