Would the US Navy serve under British command?

If the United States entered after Britain, would American naval forces operate under a British commander?

Probably within the original theater, because Britain was the attacked power and had already established the command structure, though the coalition might divide the war into an American-led Central Pacific theater and a British-led Southeast Asian theater.

A functioning coalition needs an identifiable theater commander rather than command by committee. If American forces join an existing British campaign, their task force could therefore fall under the British commander-in-chief for that area. This does not require every American operation to remain under British control. A pragmatic division could place the Central Pacific approach under an American commander and the Southeast Asian advance under a British commander, matching responsibility to the forces and routes involved.