The prewar naval race took place inside a connected global economy rather than among sealed national technology systems. Britain, the United States, Italy, and Japan competed over capital ships while still purchasing turbines, guns, sights, and other components or knowledge from one another. Japan could build on that exchange as long as peace and trade continued, then lost access to the same network under sanctions and wartime isolation. The naval treaties formally allowed the United States a fleet equal to Britain's, but Congress did not fund the US Navy to that ceiling. That underfunding, combined with Japan's genuine technical achievements, made the Imperial Japanese Navy a peer threat at the opening of the Pacific War.
Notable Point · 1:27:50-1:31:09
How peacetime exchange helped Japan become a naval peer
Interwar naval competitors still traded turbines, guns, sights, and expertise, while American underfunding helped preserve Japan's peer position at the start of war.