UK cannot land there because they did not own it at the beginning of their turn. US comes after them in the order.
You found the relevant rule and quoted it.
Amphibious Assault question
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So I had an issue come up that was new to me this weekend. I was battling it out against my father and he wanted to try out something I had not seen before. He was looking to make an amphibious assault by landing a tank in one of my unoccupied territories…no problem there. The issue was when he tried to make a blitz into an adjacent territiory that I own and that was unoccupied. Do the rules allow for such a move (land and continue…both territories are unoccupied)?
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No. Loading and/or unloading from a transport takes a land unit’s entire movement allowance. It may not move before loading or after unloading.