Hey new to the board and have a question on amphibious assaults that I can’t seem to get a handle on.

Situation is that the US has a transport and troops 2 sea units away from Paris(.i.e. 1 non-combat turn).  The sea zone next to Paris has no enemy boats(undefended).  Do I have to already be in the adjacent sea zone to Paris to conduct the assault during the combat phase(.i.e. have to spread it out over 2 turns, 1 turn using non-combat moves to get there and then attack during combat phase) or during the combat phase can I move the 2 sea units and then drop off my troops(1 turn).  Question is pretty important as it will determine if the axis win or if we keep going(Playing a minor victory).

Thanks!

Max