Ratifications are exchanged in London for the first London Naval Treaty go into effect immediately, further limiting the expensive naval arms race among its five signatories.

The London Naval Treaty, officially the Treaty for the Limitation and Reduction of Naval Armament, was an agreement between the United Kingdom, Japan, France, Italy, and the United States that was signed on 22 April 1930. Seeking to address issues not covered in the 1922 Washington Naval Treaty, which had created tonnage limits for each nation's surface warships, the new agreement regulated submarine warfare, further controlled cruisers and destroyers, and limited naval shipbuilding.