Central to the UN defensive plan was to hold the port of Pusan, where vital ground supplies and reinforcements were arriving from Japan and the US. Pusan possessed airfields where US combat and cargo aircraft were streaming into Korea with more supplies. A system similar to the Red Ball Express in World War II was employed to get supplies from Pusan to the front lines. Hundreds of ships arrived in Pusan each month, starting with 230 in July and increasing steadily thereafter. On July 24, the UN established its highest command under MacArthur in Tokyo, Japan. KPA forces in the meantime were suffering from overextended supply lines which severely reduced their fighting capacity.