For Japan, the surrounding ocean provides defensive depth around the home islands; for the British Empire, sea routes are internal lines that hold far-flung possessions together. Naval investment is therefore a strategic necessity for both powers. Britain cannot maintain its Empire without secure maritime communication, while Japan cannot surrender control of its ocean approaches. Neither sea power nor air power would be sufficient alone, so additional peace would fund development of both. These requirements keep the naval race moving even when the economic burden is severe.
Notable Point · 1:25:47-1:26:56
Strategic depth for Japan, an imperial lifeline for Britain
Japan relies on ocean approaches for strategic depth, while Britain relies on sea routes as the internal communications that hold its Empire together.