The London Naval Treaty was an agreement between the United Kingdom, Japan and the United States, signed on April 22, 1930, which aimed to regulate submarine warfare and limited military shipbuilding. It was an extension of the conditions agreed in the Washington Naval Treaty and is officially termed the Treaty for the Limitation and Reduction of Naval Armament.
The signatories agreed to build no new capital ships until 1937. A number of existing capital ships were scrapped. No existing vessels were to be converted to aircraft carriers. The construction of submarines was limited to vessels under 2,032 metric tons. The total completed tonnage of cruisers (with and without guns exceeding 155mm), destroyers and submarines to be built by 1937 was limited as was the individual tonnage in each category.
The articles relating to submarine warfare declared that international law applied to them as to surface vessels. Also merchant vessels which did not offer "persistent refusal to stop" or "active resistance" could not be sunk without the ship's crew and passengers being first delivered to a "place of safety"
See also: Geneva Naval Conference, Second London Naval Treaty