If a Harrier were to take off from a US carrier, would it then have to be catapulted? Can it take off conventionally like an ordinary plane on the usual deck runway?
Not possible to cat a Harrier - it's not equipped for cat launches,
AFAIK. Yes, but with less payload.
Can an F-14 or F-18 take off a US carrier deck without catapults? What if it used the whole length of the deck? Would the take-offs be better if it had a ski jump at the end without catapults? Just wondering.
Not possible without a cat, with/without a ski-jump.