Second London Naval Treaty The Second London Naval Treaty was an international treaty signed as a result of the Second London Naval Disarmament Conference held in London , United Kingdom . The conference started on 9 December 1935 and treaty was signed by the participating nations on 25 March 1936 . Description . The signatories were the governments of France , the United Kingdom and its Dominions , and the United States of America . The government of Japan , which had been a signatory of the First London Naval Treaty , had withdrawn from the conference on 15 January . Italy also declined to sign the treaty , largely as a result of public hostility over her invasion of Abyssinia . The conference was intended to limit the growth in naval armaments until its expiration in 1942 . The absence of Japan ( a very significant naval power ) prevented agreement on a ceiling on the numbers of warships . The treaty did limit the maximum size of the signatories ' ships , and the maximum calibre of the guns which they could carry . First of all , capital ship s were restricted to a standard displacement and 14 - inch ( 356 mm ) guns . However , a so - called " escalator clause " was included at the urging of American negotiators in case any of the countries that had signed the Washington Naval Treaty refused to adhere to this new limit . This provision allowed the signatory countries of the Second London Treaty — France , the United Kingdom and the United States — to raise the limit from 14 - inch guns to 16 - inch if Japan or Italy still refused to sign after 1 April 1937 . Also submarine s could not be larger than 2 , 000 tons or have any gun armament of greater than 5 . 1 - inches , light cruiser s were restricted to 8 , 000 tons and 6 . 1 - inch ( 155 mm ) or smaller guns and aircraft carrier s were restricted to 23 , 000 tons . Article 25 however gave the right to depart limitations if any other country authorised , constructed or acquired a capital ship , an aircraft carrier , or a submarine exceeding treaty limits , if such a departure would be necessary for the national security . For this reason , in 1938 the treaty parties agreed on a new displacement limit of 45 , 000 tons for battleship s . This London Naval Treaty effectively ended on 1 September 1939 with the beginning of World War II . Even during its brief period of supposed effectiveness , its clauses were honoured more in the breach than in the observance . Three class es of " treaty " battleships were built or laid down by the United States : the , , and classes . The design of the " North Carolina " class was initiated before the escalator clause was invoked , being intended to be armed with , and protected against , 14 - inch guns . However , with the invocation of the escalator clause , they were completed with 16 - inch guns . The four battleships of the " South Dakota " class were designed with and protected against 16 - inch guns , but maintained a 35 , 000 ton standard displacement . In order to stay within Treaty limits , the " South Dakota " was designed as a more compact and shorter vessel than the " North Carolina " . Only the Royal Navy ' s " King George V " class adhered to the 14 - inch gun for its main armament as construction could not be delayed . Design of the " Iowa " - class began in 1938 and they were ordered in 1939 ; with the treaty no longer effective carried 16 - inch guns on a displacement of 45 , 000 tons . Article 22 of the 1930 Treaty of London relating to submarine warfare declared international law ( the so - called " cruiser rules " ) applied to submarines as well as to surface vessels . Also , unarmed merchant vessels which did not demonstrate " persistent refusal to stop . . . or active resistance to visit or search " could not be sunk without the ships ' crews and passengers being first delivered to " a place of safety " ( for which lifeboats did not qualify , except under particular circumstances ) . The 1936 treaty confirmed Article 22 of the 1930 treaty remained in force , and " all others Powers [ were invited ] to express their assent to the rules embodied in this Article " . This became known as the London Submarine Protocol , and over thirty - five nations eventually did subscribe to it , including the U . S . , Britain , Germany , and Japan . It was this Protocol which was used at the post war Nuremberg Trial of Karl Dönitz for ordering unrestricted submarine warfare . These regulations did not prohibit arming merchantmen , but arming them , or having them report contact with submarines ( or raider s ) , made them " de facto " naval auxiliaries and removed the protection of the cruiser rules . This made restrictions on submarines effectively moot .