The treaty generally capped submarines at 2,000 standard tons and guns at 5.1 inches, while allowing each major signatory as many as three boats up to 2,800 tons with 6.1-inch guns. Existing boats with larger guns could also be retained under the quoted provisions. France's large Surcouf receives special treatment, preserving its 8-inch armament as a named exception. The United States, British Commonwealth, and Japan each receive 52,700 tons, creating formal equality despite their different strategic burdens. Reading the treaty language alongside real submarine displacements shows how an identical tonnage ceiling could yield very different numbers and types of boats.
Chapter · 9:10-11:17
London Treaty submarine size and gun limits
A close reading of the 1930 London treaty explains its 2,000-ton submarine ceiling, gun restrictions, limited exceptions, and equal national tonnage allowance.