Pacific invasion logistics could stage forward or sail direct

Would the Allies need captured islands as supply bases before invading Japan?

Not necessarily; planners could debate direct convoys from America against forward stockpiles followed by shorter supply runs.

Capturing islands does not automatically settle how an invasion force should be supplied. One option is to load ships in the United States and convoy them directly across the Pacific. The alternative is to build forward stockpiles and run shorter final legs from bases nearer Japan. The campaign-design tradeoff is between fewer transshipment stages and shorter operational supply routes.