Port Arthur demonstrated Japan's value as an ally

Port Arthur gave Russia a year-round Far Eastern naval base with rail access and a route to open water, advantages that Vladivostok could not provide as reliably. Its position was also dangerously close to Japan and allowed the Japanese Navy to blockade it. Mines and the blockade trapped the Russian Pacific Fleet, which was destroyed during the siege. Japan's ability to take the base and sustain the campaign gave British observers concrete evidence of its military usefulness. The loss also drove Russia to send an improvised relief fleet around the world, setting the conditions for Tsushima.