This chapter examines legal developments in submarine regulation taking into account the political context existing prior to World War II, including tensions in the Pacific with Japan’s aggression against China. Notably, States adopted the 1936 London Protocol on Submarine Warfare seeking to align requirements for submarines with obligations imposed on surface warships. Tensions in the 1930s also prompted Turkey to initiate a revision of the legal regime governing the Turkish Straits, leading to the Montreux Convention and the near complete prohibition of submarine passage in these waters. With the outbreak of World War II and unrestricted submarine warfare, questions emerged as to the viability of rules set out in the 1936 London Protocol. States also moved to revise laws of neutrality with more targeted consideration of submarines. The chapter thus reflects ongoing legal developments concerning navigational rights of submarines in territorial waters and the regulation of submarines during armed conflict.

Following World War I, the regulation of submarines was manifested in several signature developments that are discussed in this chapter. Following disarmament requirements in the Treaty of Versailles, the major powers further sought to limit armaments, especially submarines, through the negotiation of the 1922 Submarine Treaty and the 1930 London Naval Treaty. These agreements purported to restrict the number of submarines and other naval vessels held by any one State, but were ultimately unsuccessful. Also in the inter-war period, agreement was sought on the regulation of the Turkish Straits, with restrictions imposed on Turkey’s control over these waters and stipulating what vessels were allowed passage and under what conditions. Finally, the 1930 Hague Codification Conference entailed detailed discussions over the rights of warships, submarines and other vessels in the territorial sea. While this conference did not lead to the adoption of a treaty, the work achieved influenced subsequent codification efforts.