In 1958, US secretly detonated 3 nuclear devices above South Atlantic

In the summer of 1958, the United States military conducted covert high-altitude nuclear tests over the South Atlantic Ocean, under the code name Operation Argus. Three low-yield nuclear devices were launched from a secret fleet of nine ships, each carrying modified X-17A rockets with 1.7-kiloton W-25 warheads. These explosions created artificial auroras and temporary radiation belts around Earth, lasting for weeks.

The goal was to explore physicist Nicholas Christofilos' theory that detonating nuclear weapons above the atmosphere could generate trapped high-energy electrons, forming a shell around the Earth with potential defensive capabilities against Soviet intercontinental ballistic missiles or radar interference in a nuclear war. The South Atlantic location was chosen due to its weak magnetic field, facilitating electron trapping.

The final launch reached the highest altitude of any United States nuclear explosion at the time. Despite producing significant radioactive material, the artificial electron belts were discovered to dissipate faster than anticipated, rendering missile defense impractical and causing widespread radio blackouts and radar interference.

While the Operation Argus tests provided valuable insights into the Earth's magnetic field and space environment, they also highlighted potential negative consequences, including satellite damage and long-lasting radiation effects. The experiments paved the way for future high-altitude nuclear tests, like the Starfish Prime test in 1962, but they also contributed to the eventual signing of the Limited Test Ban Treaty in 1963, which prohibited nuclear tests in space, outer space, and underwater.