This unusual incident occurred at the height of the Vietnam War in 1972, during the so-called Easter Offensive of North Vietnamese troops. American troops desperately tried to strengthen their positions, in particular, mining the water area adjacent to the port of Haiphong.
Back in May of the same year, during Operation Pocket Money, they threw thousands of mines into the water outside the port, hoping that they would stay there for about a year. However, suddenly on August 4, for unknown reasons, several dozen of them detonated spontaneously.
Military experts suggested that a powerful solar flare could be the cause of the detonation. This information was immediately classified, and only recently was the classification removed when a group of civilian specialists confirmed this version.
Each naval mine is equipped with a magnetic sensor that is sensitive to changes in the magnetic field. If a passing ship was too close to the mine, then its metal hull changed the mine's magnetic field, which led to its detonation.
As it turned out, this is far from the only factor that can affect the magnetic field. In this case, the detonator was a solar flare. By the way, then because of it not only the sea mines worked, but also the telephone communication was disrupted and the power supply was cut off in many countries of the world.