On June 8, 1959 the United States Navy submarine U.S.S. Barbero surfaced off Florida and launched a Regulus cruise missile at a test target at Mayport Naval Station. Its warhead had been removed, and the space filled with United States Postal Service containers containing around 3000 postal covers. These had been stamped as cancelled by US Post Office 'USS Barbero' at 9:30 AM June 8th before the submarine had sailed. The containers were removed from the missile at Mayport and the cargo sent on to the post office in Jacksonville, Florida for sorting and forwarding to their addressees. The covers carried logos which indicated that they were part of "First Official Missile Mail," and the USPS declared that 'Missile Mail' had been accomplished. Postmaster General Summerfield stated that:

"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...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."
Hugo Gernsback likely approved.

Glowing Fish helpfully informs me: "Missile mail, like hovercars and personal home robots, seems to never have caught on. In case you didn't catch that part." I offer his words as warning to those who are eagerly setting off for their post office even now.