If the Panay Incident triggered war with Japan

What if the United States treated the 1937 attack on USS Panay as an act of war?

Britain would probably join the conflict, while the attacked United States led the coalition for political reasons.

A major Royal Navy force would likely join an American war with Japan beginning in 1937. Britain could not afford to let the United States defeat Japan alone and dominate the resulting settlement. The United States faced the mirror-image concern if Britain became the sole leading naval belligerent. The state directly attacked would take the political lead, but strategic interest would pull the other Anglo-American navy into the campaign.