Why Rozhestvensky had only one route

By the time the squadron reached Japanese waters, its practical maneuvering speed was about nine knots rather than the paper speeds of its individual ships. Going around Japan would lengthen a voyage the Russians could no longer sustain, so the direct route through Tsushima Strait was not one choice among three plausible alternatives. Japan's fleet could maintain roughly fifteen knots and operate from bases on its own coasts. Using a three-knot rule of thumb for controlling range and tempo, Japan had twice that margin and bases on both sides of the strait. Its six-knot advantage therefore gave Togo far more than tactical speed: it was the product of maintenance and supply, and it let him dictate the engagement.