Welcome, Blue Max!
@Blue:
If American units embarked a British transport on one round (and waited at the origin for the rest of the round), then the British transport moved these units on its movement phase of a second round, would the American units be able to unload during the same round on the American movement phase immediately following the Italian turn (in the order of play)?
Yes.
@Blue:
If the situation were reversed, would British units be at a disadvantage using American transports, and have to wait onboard as the destination until the next round to disembark (due to order of play)?
They would have to wait, but it’s not a disadvantage. In either case, the land units and/or fighters load on the owning power’s turn, then offload on it’s next turn, in two different rounds.
@Blue:
What I’m trying to figure out is the game terminology of “Rounds” and “Turns” in AA1914 as it applies to using allied transports. It seems that there’s an opportunity to “game” the system here that I haven’t appreciated.
A “round of play” is simply a sequence of each power having a turn, starting with Austria-Hungary and ending with the United States. Since any power must load and offload their land units and/or fighters on separate turns when using an ally’s transport, they will never load and offload in the same round, regardless of the turn order.