At the end of World War I, the United States Navy had almost 500,000 officers and enlisted men and women and in terms of personnel was the largest in the world.[108] Younger officers were enthusiastic about the potential of land-based naval aviation as well as the potential roles of aircraft carriers. Chief of Naval Operations Benson was not among them. He tried to abolish aviation in 1919 because he could not "conceive of any use the fleet will ever have for aviation." However Roosevelt listened to the visionaries and reversed Benson's decision.[109]
After a short period of demobilization, the major naval nations of the globe began programmes for increasing the size and number of their capital ships. Wilson's plan for a world-leading set of capital ships led to a Japanese counter-programme, and a plan by the British to build sufficient ships to maintain a navy superior to either. American isolationist feeling and the economic concerns of the others led to the Washington Naval Conference of 1921. The outcome of the conference included the Washington Naval Treaty (also known as the Five-Power treaty), and limitations on the use of submarines. The Treaty prescribed a ratio of 5:5:3:1:1 for capital ships between treaty nations. The treaty recognized the U.S. Navy as being equal to the Royal Navy with 525,000 tons of capital ships and 135,000 tons of aircraft carriers, and the Japanese as the third power. Many older ships were scrapped by the five nations to meet the treaty limitations, and new building of capital ships limited.[110]