Treaty displacement rules invited creative accounting

Did the Royal Navy understate the displacement of its destroyers?

Yes, as did other treaty navies; definitions and exclusions let completed ships exceed the neat figures presented under the treaty limits.

British destroyers were no more immune to optimistic figures than other treaty-era warships, and completed Tribal-class ships probably did not sit below their nominal limit. Navies differed less over whether to exploit the rules than over which interpretation they considered permissible. Standard-displacement exclusions for equipment, feed water, fuel, and defensive additions created room for creative accounting, illustrated by British reserve feed water and American Lexington and Saratoga allowances. By the late 1930s, Japan's departure from the treaty system further weakened the incentive to hold new destroyers to earlier paper limits.