Japanese and British contingency plans against the Panama Canal

Did Japan or Britain plan to disable the Panama Canal?

Japan considered submarine attack, while Britain had a contingency bombardment idea; British-US war planning was chiefly a worst-case interwar exercise.

Japan considered using submarines against the canal, while British contingency planning imagined cruisers from the North America and West Indies Station bombarding it. British planners did not treat war with the United States as their principal 1920s-1930s threat. Their practical attention lay more with Japan, Italy, and Germany. America nonetheless supplied a useful worst-case opponent because its navy was comparable in scale, just as Britain filled that role in the US War Plan Red. Contingency analysis did not mean that planners expected an Anglo-American war to occur.