On May 23, 1967, multiple radar installations in the Arctic suddenly and inexplicably went dark.The U.S. military believed the Soviets had managed to disable the Early Warning System. With war imminent, the Air Force began prepping aircraft equipped with nuclear weapons. However, those aircraft never launched, as commanders received crucial information at the last minute that may have averted full-scale nuclear war.
That information came from the North American Aerospace Defense Command’s (NORAD) newly established Solar Forecasting Center. A few days prior, it had detected a massive solar storm, one of the largest of the century. The storm produced solar flares and radio bursts that knocked out communications around the world, including the Air Force’s Early Warning System.
The Solar Forecasting Center issued a bulletin warning that severe solar flares were incoming, and that bulletin managed to reach a commanding officer in time to avert action against the Soviets. If that bulletin had been delayed a few minutes, those nuclear aircraft could have launched, and the solar flares would have made it impossible to communicate in the air. If those aircraft had launched, there would have been no way to call them back.
Source: How a Solar Flare Almost Triggered a Nuclear War in 1967