The London Treaty's unequal cruiser allowances

The treaty defined cruisers as surface combatants above 1,850 tons or armed above 5.1 inches, then separated them at 6.1 inches. The United States, British Commonwealth, and Japan received different totals and maximum heavy-cruiser counts, but the tonnage did not support equal 10,000-ton ships in every case. Japan's allowance for twelve heavy cruisers was especially tight, while detailed completion dates, transfers, and replacement clauses made the arrangement difficult to administer. Even flexibility was asymmetric: light-cruiser tonnage could be transferred to destroyers, but destroyer tonnage could not be moved back into cruisers.