Negotiated between November 1921 and February 1922, the Washington Naval Treaty between the World War I allies US, Britain, France, Italy and Japan averted a naval arms race. It ended the construction of new battleships and battlecruisers, placed armament and displacement limitations on aircraft carriers and cruisers, and prohibited construction of any new fortifications or naval bases in the Pacific Ocean region. And a 5:5:3 capital ship displacement ratio for US, UK and Japan was taken as a snub by Japan, one of several factors that drove a wedge between Japan and the US and contributed to World War II. In affecting carrier and cruiser design and numbers, it shaped many of the naval forces that were on hand at the start of World War II. Presented by Capt. Mark McDonagh, USN/ret., with 12 years’ experience at the Naval War College, on the National Security Decision Making Game staff.