It had its origins in the Cuban Missile Crisis, but it’s still in use today.

In the decades after World War II, officials in both the U.S. and USSR sought to find ways to improve communication between the increasingly antagonistic former allies. The tipping point was the 13-day Cuban Missile Crisis, which brought the world to the brink of nuclear war. The crisis was exacerbated by the exceedingly long delay in receiving and translating communication from the Kremlin—it took more than 12 hours to process Soviet Premier Nikita Khrushchev’s 3,000-word original message to President John F. Kennedy, by which time a second message had already been received. When the crisis had passed, both sides agreed that a direct, one-to-one link was necessary to prevent future escalations of tensions, and though the Cold War may have thawed, the hotline remains in use 50 years later.

The test run of the hotline didn’t go off as planned.

It took more than nine months for the two sides to hammer out the formal agreement for the hotline—formally signed on June 20, 1963—and another two months to get the system up and running. Large shipments were sent in both directions, containing multiple teletype machines and tools along with a year’s supply of tape, ink and replacement parts. Suspicion between the two nations remained so great, however, that the encryption machines designed to safeguard the secrecy of all communications were actually produced in Norway, a neutral country. By August 30, both systems were in place and the first messages were dispatched. Eager to ensure that all parts of the machinery was working correctly, the first American message contained all the letters of the alphabet and every Arabic numeral: “The quick brown fox jumped over the lazy dog’s back 1234567890.” The Soviets, meanwhile, sent over a much longer prose piece, which described the beauty of the sun as it set over the capital of Moscow. Despite the fact that both teletype systems were equipped with a decoding system to translate from language to language, the Americans were initially unable to decipher the message from the Kremlin, forcing mechanical tweaks on both ends.

There wasn’t always a “hotline” in the White House, and there has never been a red telephone.

Popular imagination may conjure up images of world leaders picking up telephones in their respective offices to communicate with each other, but when the system was first installed in the United States it was housed at the Pentagon, not in the Oval Office. It wasn’t until 1978 that a second terminal was installed at the White House (along with a third at Raven Rock Mountain, a military command center less than 10 miles away from the presidential retreat at Camp David). Things were even more convoluted on the Russian end. While the original 1963 agreement indicated that the Soviet terminal be located somewhere inside the Kremlin, rumors abound that it has always been hidden in a top-secret location elsewhere in Moscow. And though a variety of communication devices have been used of the last 50 years, none of them have been traditional telephones, let alone the “in case of emergency” red ones seen in dozens of movies and television shows and even being used in a series of infamous presidential campaign ads in both 1984 and 2008. Until fairly recently, telephone conversations couldn’t be properly secured or encrypted, leaving highly sensitive communications vulnerable to a variety of attacks.

The original line of communication was routed through much of Europe.

The hotline was only made possible by the creation of the world’s first submarine transatlantic telephone cable system. Installed in 1956 and known as TAT-1, it stretched first from Newfoundland to Scotland and then on through Scandinavia before reaching Moscow (and then along the same route in reverse). For the most part, this primary link remained stable, but parts of the line were accidentally cut over the years. To ensure communications would remain uninterrupted in all instances, a second backup link system was installed, with all messages being routed through radio links based in Morocco.

The hotline technology has continuously evolved.

The radio-based backup system remained in place until the late 1970s, when it was replaced by two different satellite hookups (one controlled by the U.S., the other by the USSR). By 1985, the entire mechanism had been updated, with high-end fax machines, capable of sending image based content as well as text messages up to 12 times faster, replacing the original teletype machines. Computers weren’t introduced until 2007, when a new network allowed for the sending of messages by email and let the individuals manning the stations communicate technological concerns via chat. While the technology has evolved, one thing has remained the same: Since its inception in 1963, the functionality of the system has been tested every hour of every day.

JFK never used the hotline, but several other presidents have.

Just three months after it was installed, the hotline was used in an unofficial capacity, when several cables were sent to Moscow providing bits of information regarding the assassination of President Kennedy. The first official use of the system during an international crisis occurred four years later, during the 1967 Six Day War between Israel and Egypt, when Lyndon Johnson alerted Soviet leader Alexei Kosygin to impending U.S. military troop movements in the region. The hotline was used most frequently in the 1970s. Richard Nixon and Leonid Brezhnev used it to ease tension and distill potential fears during three crises—the 1971 conflict between India and Pakistan; the 1973 Yom Kippur War; and the invasion of Cyprus by Turkey later that year. The 1979 Soviet invasion of Afghanistan led to a heightening of the Cold War—and a presumably tense conversation between Brezhnev and Jimmy Carter. Ronald Reagan officially used the backchannel communication system twice to discuss events in Poland and Lebanon, and both George H.W. Bush and George W. Bush reached out to their Russian counterparts once, in the aftermaths of the Persian Gulf War and invasion of Iraq, respectively.

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