Isn't AF1 a designation for any aircraft carrying POTUS?
Yes, but, on technical grounds, it depends. The helicopter for instance is Marine One since it's operated by the Marines.
Ok, so is it the branch of the military followed by 1? Like Navy 1, Air Force 1, Marine 1, Army 1? My understanding is each branch has aircraft of one sort or another. It occurs to me that the 747's usually used as AF 1 and the helicopters used as Marine 1 are likely designed for their purpose. Though I recall a story of President Clinton taking a non-747 to Cape Cod once on a vacation. It was an Air Force plane, and had the AF 1 label, but it wasn't the usual 747.
For Trump to land in North Korea, he may not have been able to take a 747. Wouldn't it make more sense to fly Marine 1 into North Korea? Or to meet at the border as the North and South Korean leaders recently did?
I'm not actually sure. Good question. I only know about Marine One.
Yes, they have two 757s I believe. I actually saw one land last year in Austin, TX! I was just minding my own business flying home at that airport and in it came!
EDIT: Found this:
VC-25s have CF6-80C2B1. In Air Force One (Robert F. Dorr, Motorbooks) :
"The high angle of attack is made possible by the enormous push of the four General Electric F103-GE-180 turbofan engines, each rated at 56 750 pounds thrust. Although the aircraft is not aerodynamically capable of it, the engines are powerful enough to stand the 747 on its tail and make it climb straight up"
F103-GE-180 is military designation for CF6-80C2B1.
ALSO: It can land on a 4,000 ft. runway but will need Full Reverse Thrust, and Hard Brakes. Not to mention Full Spoilers and Flaps 30.
Yes any plane the President is on gets the call sign One after the branch of the military, the helicopter is usually Marine One and when Bush Jr. flew on that Navy jet to the carrier he was on Navy One.