Nuclear triad
Israel is known to have nuclear-capable aircraft and land-base missiles, with the addition of nuclear-armed submarines this would mean that they now have a full triad of land-, air-, and sea-based nuclear delivery systems some of which would be invulnerable to a first strike by an enemy for the first time in their country's history. No other nation in the Middle East in known to be in possession of nuclear weapons, even though Iran, Iraq, Syria and Libya have started development programs that were never completed.
List of states with nuclear weapons
In 1979, there was a detection of a putative covert nuclear test in the Indian Ocean, called the Vela incident. It has long been speculated that it was a test by Israel, in collaboration with and support of South Africa, though this has never been confirmed. South Africa could not have constructed such a nuclear bomb until November 1979, two months after the "double flash" incident.
South Africa signed the Nuclear Non-Proliferation Treaty in 1991.