F-110 Spectre? Isn’t that an F-4 Phantom? Well, yes, but....
In 1953, McDonnell Aircraft began work on an updated version of their F3H Demon, and the result was an aircraft that eventually became the F4H, an all-weather fleet defense fighter for the US Navy. The F4H entered Navy service in 1960 as the Phantom II, after some consideration was given to assigning it the nickname Mithras (the Persian god of the sun) or Satan. (Personally, I think Mithras would have been a pretty cool name.)
At the time, US Defense Secretary Robert McNamara was dead set on having all flying branches of the US military operate the same aircraft in an effort to save money. When the Air Force received their first Phantoms for testing, they had to give the fighter their own designation, because there’s no way the Air Force would use a Navy number. Thus, the first Phantoms in Air Force service were known (unofficially) as the F-110A, and were given the appropriately spooky name Spectre.
The Air Force really liked their Navy fighters, and in 1962 sanity prevailed when McNamara instituted the United States Tri-Service aircraft designation system which standardized the designation of US military aircraft. At that point, the F4H-1 in Navy and Marine Corps service became the F-4A and F-4B, and the Air Force F-110 Spectre became the F-4C Phantom II. Now, it’s only the alphabet soup of variant letters that is confusing.