Recently declassified military documents have revealed that during the Vietnam War, the U.S. Navy has suspected that a powerful storm caused dozens of its sea mines to explode.
The U.S. Navy planted sea mines as part of Operation Pocket Money, the aerial mining campaign launched in May 1972 to block the North Vietnamese from maritime trade.
A few weeks later, on August 4, crew members aboard the Task Force 77 aircraft observed a batch of explosions south of Hai Phong where Destructor sea mines had been deployed.
They documented between 20 and 30 explosions in just 30 seconds and observed another 25 to 30 patches of muddy water that indicate further explosions.
There was no clear reason why the mines detonated. The sea mines had a self-destruct feature but their minimum self-destruct time was not for another 30 days.
According to the Conversation, the U.S. Navy suspected extreme solar activity at the time as the possible cause of the unexpected explosions.
The now declassified U.S. Navy report revealed that on August 15, 1972, Admiral Bernard Clarey, the Commander in Chief of the US Pacific Fleet, asked about the possibility that solar activity could have caused the mines to detonate.
An intense solar activity was recorded in August 1972. The sunspot region MR 11976 ejected a series of solar flares, coronal mass ejections, and clouds of charged particles. Many of the deployed mines were magnetic influence sea mines designed to detonate when they detect changes in the magnetic field.
Investigations conducted at the time detailed a high probability that the Destructor mines were detonated by the powerful solar storm activity, one of the most intense ever recorded.
In a new study published in Space Weather on October 25, Delores Knipp, from the University of Colorado, and colleagues agreed with the decades-old assessment.
"The extreme space weather events of early August 1972 had significant impact on the U.S. Navy, which have not been widely reported," the researchers wrote in their study.
"These effects, long buried in the Vietnam War archives, add credence to the severity of the storm: a nearly instantaneous, unintended detonation of dozens of sea mines south of Hai Phong, North Vietnam on 4 August 1972."Coronal mass ejections normally reach Earth's geomagnetic field and produce magnetic storms in a day or two but the electromagnetic pulses that caused the detonation of the sea mines reached Earth in a just 14.6 hours
Knipp and colleagues said that the reason for the"ultra-fast" mass ejection on August 4 is the two prior pulses from the sun on August 2 that cleared the path to our planet.
Besides detonating the mines, the solar storm also caused power disruptions and outage of telegraph lines.