For the first time, retired US Air Force officers have published [PDF] an account of an incident on May 23, 1967 when a solar storm nearly fooled American high command into thinking that a Soviet nuclear attack was on the way.
On that day, the US military nuclear command went into panic mode when signals from all three of the Ballistic Missile Early Warning System (BMEWS) sites in the far northern hemisphere (one apiece at Alaska, Thule in Greenland, and a base in the UK's county of Yorkshire) shut down simultaneously.
These BMEWS stations were positioned over the most likely routes for Soviet ICBMs to come visiting the Land of the Free, and some thought the USSR had worked out a jamming technology that would blind the US ahead of an attack.
The US wouldn't have been completely defenseless. Since 1960 the military had been running Operation Chrome Dome, a never-ending nuclear-equipped bombing fleet that loitered constantly around the US ready to fly to targets in the USSR. If the Cold War ever turned hot, these bombers provided a valuable retaliatory force, and more aircraft were on standby to take to the skies as needed.
When the BMEWS went down, this secondary bomber force was put on alert and flash warnings were sent to other nuclear facilities warning them that this might be the big one. But luckily a message from a series of forecasts made it through to central command telling them that it might not be the Soviets causing the issues.
"This is a grave situation," said Delores Knipp, a space physicist at the University of Colorado in Boulder, and coauthor of the paper. "But here's where the story turns: things were going horribly wrong, and then something goes commendably right."
Since the 1940s, the US military planners had had evidence of how solar radiation could affect communications systems here on earth. In the mid-1960s the Air Force's Air Weather Service (AWS) had been doing regular solar forecasts to spot this kind of radiation.
On May 18, 1967 the AWS spotted an unusually large group of sunspots with intense magnetic fields in one region of the sun. Shortly afterwards this area erupted, causing one of the largest solar storms ever recorded flying towards earth.
"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," said retired Colonel Arnold Snyder, a solar forecaster at NORAD's Solar Forecast Center, who was on duty that day.
The loss of the BMEWS was flashed both to the military and to government heads. Knipp says that contemporary documents indicate that President Johnson would have received the news. Given the heightened state of alert at the time – Vietnam's summer offensives weren't going well and forces were massing in the Middle East for the Six Day War that broke out days later – the news could have scared some folks into pushing the button.