By October 24, 1973, Israel had turned the tide of the war it was fighting against both Egypt and Syria, and both countries’ forces were on the run. Leonid Brezhnev, then the ruler of the Soviet Union, panicked at the prospect of the defeat of his two most important Middle Eastern allies—to an extent made clear by documents made public only recently. Eric Cortellessa writes:
According to letters and notes collected and translated by the Woodrow Wilson Center, Brezhnev sent a letter to then-President Richard Nixon warning him that he would send troops to the Middle East if both countries did not act together to curb the Israelis. . . .
[In particular], the Soviets had a vested interest in Egypt, one of its major client states. The new documents show that Brezhnev sought to take advantage of Nixon’s political strife back in America —this was during the apex of the Watergate scandal—to secure an Arab victory. . . .
[T]hen-Secretary of State Henry Kissinger . . . first received Brezhnev’s threatening letter to Nixon. Given the U.S. president’s precarious position—and the fact that he was indisposed when the letter came in—Kissinger consulted with then-White House Chief of Staff Alexander Haig and other national-security officials, who jointly decided to move America’s nuclear alert level to Defcon 3.
The new documents show that this was not just a reaction to the Soviets’ sending a naval brigade into the Mediterranean, which was believed to be the reason at the time. It was, in fact, because intelligence reports found that a Soviet ship believed to be carrying nuclear weapons was en route for the Egyptian port of Alexandria.
The Soviets backed down, and the next day Israel and its enemies agreed to a cease-fire.
Read more on Times of Israel: https://www.timesofisrael.com/how-leonid-brezhnev-almost-escalated-the-yom-kippur-war-into-a-nuclear-nightmare