What did the submarine USS Barbero do on June 8, 1959, at 9:10 a.m. that has never been duplicated?

Watchkeeper

Launched "Missile Mail". "The USPS tried their first and only delivery of "Missile Mail", though the idea of delivering mail by rocket was not new. Shortly before noon on 8 June 1959, off the northern Florida coast, Barbero fired a Regulus cruise missile towards the Naval Auxiliary Air Station, Mayport, Florida. Twenty-two minutes later the training type missile landed at its target; its training-type warhead having been configured to contain two official USPS mail containers." http://en.wikipedia.org/wiki/USS_Barbero_%28SS-317%29 Jul 25 09, 6:05 PM