Originally Posted by KenV
Air Force One is the call sign of ANY airplane with POTUS aboard, and Clinton, Bush, and Obama have all flown on C-17s.
Not quite - AF1 is only for USAF aircraft.
When POTUS is aboard one of the VH-3Ds or VH-60Ns, he is aboard "Marine One" - and when Bush43 was aboard that USN S-3B Viking on 1 May 2003 flying to CVN-72 to give the "Mission Accomplished" speech, he was aboard "Navy One"!
If he was in a US Army Chinook it would be "Army One".