The Battle of the Yellow Sea ( Kokai kaisen; ) was a major naval engagement of the Russo-Japanese War, fought on 10 August 1904. In the Russian Navy, it was referred to as the Battle of 10 August. The battle foiled an attempt by the Russian fleet at Port Arthur to break out and form up with counterparts from Vladivostok, forcing them to return to port. Four days later, the Battle off Ulsan similarly ended the Vladivostok group's sortie, forcing both fleets to remain at anchor.