How a Solar Storm Set Off Sea Mines During The Vietnam War

Buried deep within the archives of the US Navy, lied a mystery that was only recently solved. On August 4, 1972, dozens of naval mines that the United States had planted in the sea off the port of Haiphong during the Vietnam war went off simultaneously and prematurely. The mines were magnetic sea mines that were designed to sense changes in the magnetic field due to the presence of a large object of iron, such as the hull of a ship. These mines can only be triggered by passing ships, but on this occasion the sea was clear.

At the time, the military suspected solar interference might be involved in the explosion, but the research was classified until now. Since the declassification, a group of civilian researchers revisited the incident and confirmed that the mines were indeed triggered by a powerful solar storm.

Solar storms caused by coronal mass ejections are known to interfere with electrical and electronic devices here on earth. Solar storms have fried satellites, blacked-out electrical grids, and disrupted navigation and communications systems. The solar storm of August 1972 was a Carrington-class storm, meaning it may have been similar to the strongest storm on record, the Carrington Event of 1859.

“This is a Carrington-class storm that has gone under the radar,” said Delores Knipp, one of the research professor at the University of Colorado Boulder who led the study. “What I am asking scientists to do is go back and reinvestigate with new eyes.”

The huge cloud of charged particles ejected by the sun reached earth after only 14.6 hours, the fastest a solar storm have ever travelled. Such an event usually takes two to three days to reach earth. Once it slammed into the atmosphere, it caused blackouts on radio frequency bands, and produced significant electrical grid disturbances throughout Canada and across much of eastern and central United States. In the South China Sea, off the east coast of North Vietnam, it triggered some 20 to 30 naval mines within a period of just 30 seconds. Another 25 to 30 patches of muddy water were also observed, indicative of further explosions.

An American naval mine explodes in North Vietnams Haiphong Harbor, 1973. Photo: United States Navy/Wikimedia Commons

The timing of the solar storm was such that it fell between Apollo missions 16 and 17: the crew of Apollo 16 had returned to Earth in April and the crew of Apollo 17 was preparing for a moon landing in December. Had astronauts been in transit to the moon, it would have caused serious harm to their health, requiring an emergency return home for medical attention. If the astronaut was on the lunar surface, or outside the spacecraft conducting a spacewalk, he would have received a near fatal does of radiation.

The researchers said that the solar storm, and the subsequent explosion of dozens of sea mines, illustrates the modern challenge of figuring out how storms like this would impact modern infrastructure.

“If a storm that bad were to appear again, then we would really have a lot of problems,” said Knipp.

References:
# Delores J. Knipp, Brian J. Fraser,  Shea, D. F. Smart, On the Little-Known Consequences of the 4 August 1972 Ultra-Fast Coronal Mass Ejecta: Facts, Commentary, and Call to Action, Space Weather
# Daniel Strain, A 1972 solar storm triggered a Vietnam War mystery, University of Colorado Boulder
# Neel V. Patel, That time a bunch of underwater mines exploded and the sun was the only suspect, Popular Science
# George Dvorsky, A Powerful Solar Storm Likely Detonated Dozens of U.S. Sea Mines During the Vietnam War, Gizmodo