It was during some of the scariest days of the Cold War that the submarine surfaced off the coast of the United States. On the submarine was the most powerful cruise missile yet developed, capable of delivering a nuclear strike anywhere with 500 miles. The crew readied the missile for launch, just as they had been trained to do. This time, however, it was not an exercise. The missile would be fired against a target within the continental United States.

If you think this is the plot of a Hollywood action movie, think again. This incident was real. On the chance that it failed to show up in your history books, let’s take a look at the successful Cold War missile strike upon U.S. soil.

It was June 8, 1959. Dwight D. Eisenhower was president. Nikita Khrushchev was at the head of the Soviet Union. The Cold War was at its height, with both countries racing toward developing their nuclear arsenals.

On this fateful day, as the world’s two superpowers watched each other for any indication that World War III was about to begin, the submarine surfaced off the Atlantic coast of the United States. The SSM-N-8A Regulus missile was carefully aimed at a target about 100 miles away: the Naval Auxiliary Air Station at Naval Station Mayport in Florida.

The command to launch was issued, and the mighty rocket flew from the submarine. Powered with the most powerful engines yet developed, it quickly reached its cruise altitude. Twenty-two minutes later, it found its target.

Why did this not merit any mention in the history books? Why did this not trigger World War III? Why isn’t there a radioactive crater in Florida?

Don’t think that the launch was unsuccessful. Everything happened exactly as planned. It wasn’t a matter of the missile turning out to be a “dud,” either. The payload performed perfectly.

One reason this missile strike didn’t usher in the end of civilization as we know it is that it was launched by a U.S. submarine. The USS Barbero sent the Regulus missile into friendly territory. No, the sub had not been taken over by hostile forces, nor was the captain suffering a mental breakdown. Barbero sent the missile against its Florida target on verified orders from the National Command Authority.

The primary reason the world did not come to an end over this incident was that the missile was not carrying its typical nuclear payload. Instead of destruction, it delivered 3,000 pieces of mail. The incident marked the first — and last — time that the U.S. attempted to deliver air mail by missile.

In preparation for the experiment, the postal service established a branch post office aboard the Barbero. All of the pieces of mail were duplicate — commemorative postal covers addressed to President Eisenhower and other government officials. The four-cent postage stamps were cancelled with a stamp bearing the words, “USS Barbero Jun 8 9.30am 1959.” After the missile landed, the mail was retrieved and delivered to the post office in Jacksonville, Florida for processing.

The Postmaster General, Arthur A. Summerfield, was on hand to witness the arrival of the missile. He said, “This peacetime employment of a guided missile for the important and practical purpose of carrying mail, is the first known official use of missiles by any Post Office Department of any nation.” He was optimistic that it was just the first of what would become a regular practice, stating that “before man reaches the moon, mail will be delivered within hours from New York to California, to Britain, to India or Australia by guided missiles. We stand on the threshold of rocket mail.”

Alas, Summerfield’s predictions did not come to pass. In reality, the purpose of the specatacle was an opportunity for the U.S. to show off its missile targeting capabilities to the rest of the world. Besides, advances in aviation soon made it possible to deliver air mail around the world in about a day without having to resort to missile technology.