Japan could not fortify important island territories forming its outer defensive belt, while the United States already possessed major works such as Fort Drum and Britain retained access to Singapore. The geographic asymmetry mattered because the British and American homelands lay far beyond the prohibited zone while Japanese mandated islands formed immediate defence in depth. One proposed compromise permits modernisation within existing base footprints and limits new defensive guns to cruiser calibre. Japan could then spend on visible defence without creating positions able to stop battleships or carrier strikes by themselves.
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Why the Pacific fortification clause disadvantaged Japan
The treaty restricted Japan's defensive depth while Britain and the United States retained distant homelands and established bases.