On the previous British turn, the British loaded land units onto American transports in an adjacent sea zone. On its turn, the British conduct an amphibious assault from the American transports in the sea zone during the combat phase. During the British noncombat movement phase, the British want to load more British land units onto the American transports from an adjacent friendly territory. The British are using the same American transports both in the combat phase and noncombat phase of the British turn. Is this allowable?
No it is not. Once the troops are unloaded, further troops cannot be loaded during the same turn:
… once it offloads, it can’t move, load, or offload again that turn.