The Vela Incident (sometimes referred to as the South Atlantic Flash) was an unidentified “double flash” of light that was detected by an American Vela Hotel satellite on September 22, 1979.
Some specialists who examined the data speculated that the double flash, characteristic of a nuclear explosion, may have been the result of a nuclear weapons test: “The conclusions of the Presidential panel (the Ad Hoc Panel) were reassuring, as they suggested that the most likely explanation of the Vela detection was a meteoroid hitting the satellite — in part because of the discrepancy in bhangmeter readings. Others who examined the data, including Defense Intelligence Agency (DIA), the national laboratories, and defense contractors reached a very different conclusion — that the data supported the conclusion that on 22 September 1979, Vela 6911 had detected a nuclear detonation.“[1][2]

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The “double flash” was detected on September 22, 1979, at 00:53 GMT, by the American Vela Hotel satellite 6911, which carried various sensors that had been designed specifically to detect nuclear explosions. In addition to being able to detect gamma rays, x-rays, and neutrons, the satellite also contained two silicon solid-state bhangmeter sensors that would be able to detect the dual light flashes associated with a nuclear explosion—to be specific the initial brief, intense flash, followed by the second longer flash.[2]
The satellite reported the characteristic double flash of an atmospheric nuclear explosion of two to three kilotons, in the Indian Ocean between The Crozet Islands (a very small, sparsely inhabited French possession) and the Prince Edward Islands which belong to South Africa at 47°S 40°ECoordinates: 47°S 40°E.

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In February 1994, Commodore Dieter Gerhardt, a convicted Soviet spy and the commander of South Africa’s Simon’s Town naval base at the time, talked about the incident upon his release from prison. He said:
Although I was not directly involved in planning or carrying out the operation, I learned unofficially that the flash was produced by an Israeli-South African test, code-named Operation Phoenix. The explosion was clean and was not supposed to be detected. But they were not as smart as they thought, and the weather changed – so the Americans were able to pick it up.[29]

April 20, 1997, the Israeli daily newspaper Haaretz quoted the South African Deputy Foreign Minister, Aziz Pahad, as supposedly confirming that the “double flash” from over the Indian Ocean was indeed from a South African nuclear test. Haaretz also cited past reports that Israel had purchased 550 tons of uranium from South Africa for its own nuclear plant in Dimona. In exchange, Israel allegedly supplied South Africa with nuclear weapons design information and nuclear materials to increase the power of nuclear warheads.[30] This statement was confirmed by the United States Embassy in Pretoria, South Africa,[16][31] but Pahad’s press secretary stated that Pahad had said only that “there was a strong rumor that a test had taken place, and that it should be investigated”. In other words – he was merely repeating rumors that had been circulating for years.[32][33]

In October 1999, a white paper that was published by the U.S. Senate Republican Policy Committee in opposition to the Comprehensive Test Ban Treaty stated:
There remains uncertainty about whether the South Atlantic flash in September 1979 recorded by optical sensors on the U.S. Vela satellite was a nuclear detonation and, if so, to whom it belonged.[34]
In his 2006 book On the Brink, the retired C.I.A. clandestine service officer, Tyler Drumheller, wrote of his 1983–88 tour-of-duty in South Africa:
We had operational successes, most importantly regarding Pretoria’s nuclear capability. My sources collectively provided incontrovertible evidence that the apartheid government had in fact tested a nuclear bomb in the South Atlantic in 1979, and that they had developed a delivery system with assistance from the Israelis.