Yamamoto's East Asian two-power calculation

Yamamoto Gonnohyoe framed Japan's future fleet against Russia as the most likely threat while allowing for combinations involving Britain, France, or Germany. He adapted the era's two-power thinking to Japan's position rather than assuming a single opponent. Because European navies had major commitments elsewhere, he estimated that Britain or Russia might detach about four battleships to East Asia, perhaps reinforced by a lesser power. Japan therefore needed enough strength to deter a coalition without trying to match an entire European fleet. The calculation produced a six-battleship requirement rooted in plausible theater reinforcement rather than prestige alone.