Domestic U.S. Air Mail was formally established as a class of service by the United States Post Office on 15 May 1918, when bags of mail were flown between Washington, Philadelphia, and New York. In 1959, the U.S. Navy took postal delivery to the next level by packing a Regulus I cruise missile with mail aboard the submarine USS Barbero, docked at Norfolk, Virginia, and launching it to the naval air station in Mayport, Florida. The missile, containing 3,000 letters symbolically addressed to President Dwight D. Eisenhower and other government officials, made the 100-mile (161 km) trip in 22 minutes. Although "rocket mail" never caught on as a practical method of postal delivery, the experiment succeeded as a not-so-subtle way to show off the U.S. military’s state-of-the-art missile guidance system during the Cold War.
The first and only missile mail: