The Vela Incident, sometimes referred to as the South Atlantic Flash, was a mysterious nuclear explosion which occurred near the very remote Bouvet island, thousands of miles south of Africa. It is thought to have been a clandestine nuclear test by either the South African or Israeli government.
The Vela Incident is named after the United States' Vela spy satellite, which observed the characteristic double flash of a nuclear bomb in the early morning hours of 22 September 1979. In the weeks after the blast, there was much confusion as to whether this really was a nuclear explosion, and if so, to whom it belonged. Navy hydrophones picked up acoustic disturbances similar to what would be expected if a small nuclear weapon were detonated on or just under the surface of the ocean.
Much information about the Vela Incident is still classified, so it can be hard for civilians to make a reliable estimate about which country might have detonated the bomb. Initially the Soviet Union or China were suspected, but they would have no reason to detonate a bomb in the area unless they wanted to make it look as if South Africa or Israel had done it. A thousand km or so away there was a French nuclear testing ground, so there has also been speculation that the Vela Incident was the detonation of a French neutron bomb.
The explosion was in the two to three kiloton range. Although some speculate that it was actually a meteor, the scientists responsible for designing the Vela satellite are adamant that it made its assessment of the presence of the characteristic nuclear double-flash properly. To this day there are those who believe the Vela Incident was the result of an exploding meteor, similar to the Tunguska event in eastern Siberia.
A panel dispatched to study the Vela Incident was skeptical about its nuclear origin, pointing out that only one of the two Vela satellites picked up the explosion. It may have been detected due to a malfunction caused by a small meteoroid impacting the satellite. Many, however, doubt the veracity of the panel's claims, arguing they were politically motivated.
We may never discover the truth about the Vela Incident until the papers concerning it are declassified, and even then, there may be insufficient information to conclude one way or the other.