In the 1950s the US Navy asked Douglas if it was possible to convert the two seat side-by-side version of the Skyraider, the AD-5, into an air refueling tanker with a hose drum unit and extra fuel tanks behind the cockpit. A drogue would have been trailed out from the opening below the rudder that was originally designed for the MAD boom for the AD-5S. Douglas' work concluded there would be significant center of gravity problems with the design and instead came up with the D-704 inflight refueling pod which turned the Skyraider into the world's first operational buddy tankers.
Source: Air International, February 2009. "Aircraft Profile: Douglas Skyraider" by Rene Francillon, p65.