If Australia and New Zealand retained battlecruisers

How would Japan and the United States respond if Australia and New Zealand kept their battlecruisers?

Their response depends on whether the ships count as independent dominion forces or as part of the Royal Navy's treaty strength.

Legal and organizational status is the decisive variable. If Australia and New Zealand retain the ships as independent powers, neither Japan nor the United States can automatically count them as British replacements requiring a direct response. If they remain within Royal Navy totals, Britain would probably seek to replace or redistribute equivalent capital ships. One illustrative outcome gives the dominions newer battlecruisers such as Lion and Tiger, showing how treaty accounting can shape fleet ownership.