"It's called backfill. The Japanese takes over other American duties in the Pacific, freeing up American ships for the conflict. Most often discussed is munitions convoy protection. Fight as you train. Train as you fight. From the exercise, you can tell what Japanese participation will be."Sure, Japan has a range of options to support the US short of participating in direct combat, just as the US did prior to its entry into WW2 with its material support of UK and others aka lend-lease, embargoing Japanese oil, etc. Most of these options will make it difficult for China to have a sufficient casus belli to militarily retaliate against Japan.
