The first official presidential aircraft was nicknamed the “Sacred Cow.”

FDR’s “Sacred Cow” plane

Today, the airplane carrying the U.S. president is known as Air Force One, but the original presidential aircraft had a slightly more colorful name: the Sacred Cow. The plane was specially designed for Franklin D. Roosevelt to meet the president’s increased needs for international travel during World War II. Though it was officially named the Flying White House, the White House press corps began calling the aircraft the “Sacred Cow,” a name inspired by the heavy security that was dedicated to keeping the plane and its VIP passengers safe. The Sacred Cow featured a conference room, windows made of bulletproof glass, and an elevator so that Roosevelt, who used a wheelchair, could easily board and deplane. For added convenience, the elevator even lifted the President directly into a private office on the plane. Although the aircraft had been customized for his personal use, Roosevelt ended up flying on the Sacred Cow just one time, when he used it in 1945 to fly to the Yalta Conference, a wartime meeting in Crimea during which Roosevelt, British Prime Minister Winston Churchill, and Soviet Premier Joseph Stalin discussed the final stages of World War II and the future of the postwar world.

Roosevelt’s successor, President Harry Truman, continued to use the Sacred Cow from 1945 to 1947, at which point the aircraft was reassigned for other functions before being officially retired in 1961. Notably, Truman was flying on the Sacred Cow when he signed the National Security Act of 1947, which established the Air Force as an official, independent department of the U.S. military — the Sacred Cow has even been called the “birthplace of the Air Force.” The call sign “Air Force One” was first used to identify the presidential airplane in 1953, and the term became the official designation in 1962.

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Air Force One is shadowed by a “Doomsday plane” in case of a nuclear attack.

In keeping with the emphasis on security that gave the original Sacred Cow its name, the modern-day presidential aircraft are outfitted with some seriously heavy-duty safety features, including armored windows and a radar-jamming system to evade potential missile attacks. On top of that, the president’s plane is trailed at all times by a second aircraft commonly referred to as the “Doomsday plane.” The Doomsday plane was introduced in 1973, during the Cold War, when a nuclear attack was considered a looming threat. The plane is designed to serve as a safe haven and command center for the president if such an attack were to occur. It’s capable of withstanding a nuclear blast, and it flies using analog controls since electronics are prone to disruption from the electromagnetic pulses emitted by nuclear explosions. The military keeps the full design of the Doomsday plane a closely guarded secret, however, and usually refuses to even discuss it publicly.