How the Sun Set Off Dozens of Mines During the 1972 Vietnam War
In 1972, the United States was deep into the Vietnam War with little end in sight. North Vietnam had just launched an offensive on the South, the Easter Offensive.
The United States military was desperate to gain any advantage it could, so top brass hatched a plan to cover the port of Haiphong with underwater mines.
Starting in May of that year, Operation Pocket Money saw thousands of mines dropped in the water outside Haiphong’s port.
Those mines were supposed to sit there for about a year, but on August 4, dozens of them exploded prematurely. But they weren’t set off by passing ships; instead, it seems that the mines were triggered by the sun.
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 the military’s suspicions: Solar effects were to blame.
The key lies in how the mines are triggered to explode. Each mine has a magnetic sensor that can detect subtle changes in magnetic fields.
If a passing ship drifts too close to the mines with its metal hull, the altered magnetic field would set off the detonator.
Unfortunately, there are plenty of ways to alter a magnetic field aside from the hulls of ships. One significant source of magnetic fields is the sun, which produces the strongest magnetic field in the solar system.
Occasionally, large eruptions from the surface of the sun—called solar flares—can send huge plumes of magnetic material hurtling toward Earth.
When those solar flares reach Earth, they can cause all kinds of magnetic disturbances. At their most mild, they’re responsible for the Northern Lights and other auroras.
At their worst, they can mess with GPS systems, interfere with communications, and in one particularly notable case, almost start a nuclear war.
In this case, an unusually strong solar flare was enough to mess up the delicate sensors on some of the Navy’s mines placed in Haiphong’s harbor.
According to the research paper, that 1972 solar flare was one of the strongest on record, and in addition to exploding a few dozen mines also interfered with telephone lines and triggered power outages around the world.
This event underscores just how disruptive and dangerous solar flares can be. A high-intensity solar flare like the 1972 event could cripple our satellite networks if it hit us today, and so far we’ve been lucky to avoid something like that.
But we can’t be lucky forever, and if a repeat of the 1972 flare hits us now, exploding mines are going to be the least of our worries.
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