Originally Posted by
Brewster Buffalo
Quick search suggests that SPAD is a reference to the WW1 French biplane but others aren't convinced though no-one has come up with an alternative theory. Perhaps it started when the A-1 was in French service in the 1950s?
That sounds a reasonable explanation. The Skyraider would have been known to both the US and French as the AD (signifying a Douglas-built attack aircraft) prior to 1962 under the US Navy designation system, before it was superseded by the tri-service system and redesignated A-1.