@jbuckbuddy, from Rule 0.5, as stated above: “Major Powers that are not at war with each other may freely share sea zones and do not affect each other.”
Using allied transports
I have a question about using the same alliance’s transports. If I’m the USA and have Inf in London and Normandy is allied possessed (France), can I use a British transport to non combat move into Normandy in one turn or will it be loading up on the transport in one turn, then unloading into Normandy the second? I assume since the transport never moves into another sea zone you can just load and unload in one turn since you don’t ever have to wait for the transport to move which it states in the rules.
It would take two turns. See rule 8.4 (1936v.3) « Transporting allied units ».
Note that if you play with the Canada at War expansion, and you replace the Americans with Canadians in your example, it can all be done in the same tun, as all the Commonwealth units move together (Canada National reference sheet v.3.1).