In mid-July, the UN Far East Air Force Bomber Command began a steady and increasing campaign against strategic North Korean logistics targets. The first of these targets was Wonsan on the east coast. Wonsan was important as a communications center that linked Vladivostok, Siberia, with North Korea by rail and sea. From it, rail lines ran to all the KPA build-up centers. The great bulk of Russian supplies for North Korea in the early part of the war came in at Wonsan, and from the beginning it was considered a major military target. By July 27, the FEAF Bomber Command had a comprehensive rail interdiction plan ready. This plan sought to cut the flow of KPA troops and materiel from North Korea to the combat area. Two cut points, the Pyongyang railroad bridge and marshaling yards and the Hamhung bridge and Hamhung and Wonsan marshaling yards, would almost completely sever North Korea's rail logistics network. Destruction of the rail bridges over the Han River near Seoul would cut rail communication to the Pusan Perimeter area. On August 4, FEAF began B-29 interdiction attacks against all key bridges north of the 37th Parallel in Korea and, on August 15, light bombers and fighter-bombers joined in the interdiction campaign.