UN Offensive , 1950 The first United Nations ( UN ) offensive during the Korean War began on September 15 , 1950 , with the U . S . X Corps , under Army Maj . Gen . Edward M . Almond , making an amphibious assault at Inchon , 150 miles north from the frontlines . In the south , the Eighth U . S . Army , made up of U . S . , ROK , and British forces , counterattacked the next day . The 1st Marine Air Wing provided air support for the landing at Inchon while the Fifth Air Force likewise supported the Eighth Army . On September 16 , as part of a strategic bombing campaign , the FEAF bombed Pyongyang , the capital of North Korea , and Wonsan , an east coast port 80 miles north of the 38th parallel . U . S . Marines attached to X Corps captured Kimpo Air Base near Seoul on September 17 . Two days later the first FEAF cargo carrier landed there , inaugurating an around - the - clock airlift of supplies , fuel , and troops . C - 54s returned wounded personnel to hospitals in Japan , and C - 119s airdropped supplies to front - line forces . Bad weather hindered close air support of the Eighth Army , but on the 26th the U . S . 1st Cavalry Division forged out of the Pusan Perimeter north of Taegu and within a day thrust northward to link up with 7th Infantry Division forces near Osan , 25 miles south of Seoul . Air controllers , using tactics similar to those developed in France during World War II , accompanied the advancing tank columns , supported tank commanders with aerial reconnaissance , and called in close air support missions as needed . On September 26 , General Douglas MacArthur announced the recapture of Seoul , but street fighting continued for several more days . For a time in August and September 1950 , before the recapture of Kimpo , all FEAF flying units had to fly from bases in Japan . The only continuously usable tactical base in Korea was Taegu ( K - 2 ) , which the FEAF used as a staging field to refuel and arm tactical aircraft . On September 28 fighter - bombers returned permanently to Taegu . As US forces swept North Korean troops from South Korea , aviation engineers rebuilt the airfields , beginning with Pohang , on the east coast 50 miles northeast of Taegu . USAF flying units returned on October 7 to Pohang and to other rebuilt airfields at Kimpo , near Seoul , and at Suwon , 20 miles south of Seoul . On September 27 , Truman sent a top secret National Security Council memorandum , 81 / 1 , to MacArthur reminding MacArthur that operations north of the 38th parallel were authorized only if “ at the time of such operation there was no entry into North Korea by major Soviet or Chinese Communist forces , no announcements of intended entry , nor a threat to counter our operations militarily … ” On September 30 , Defense Secretary George Marshall sent an eyes - only message to MacArthur instructing MacArthur “ We want you to feel unhampered tactically and strategically to proceed north of the 38th parallel . ” Supported by a UN resolution , President Harry S . Truman directed the U . S . Joint Chiefs of Staff to authorize pursuit of the retreating North Korean forces , and on October 9 the Eighth Army crossed the 38th parallel near Kaesong . American and South Korean forces entered the North Korean capital of Pyongyang on October 19 . FEAF B - 29s and B - 26s continued to bomb surface transport lines and military targets in North Korea , while B - 26s , F - 51s , and F - 80s provided close air support to ground troops . FEAF also furnished photographic reconnaissance , airlift , and air medical evacuation . For example , on October 20 the air force ' s troop carriers delivered 2 , 860 paratroopers and more than 301 tons of equipment and supplies to drop zones near Sukchon and Sunchon , 30 miles northeast of Pyongyang . The airborne troops by - passed strong defenses established by the North Koreans , and taken by surprise , the enemy troops abandoned their positions to retreat further northward . Bruce Cumings argues that the KPA ' s rapid withdrawal was strategic , with troops melting into the mountains from where they could launch guerrilla raids on the UN forces spread out on the coasts . Meantime , on the east coast of Korea , the ROK forces crossed the 38th parallel on October 1 , and ten days later captured Wonsan . On October 26 South Korean forces reached the Yalu River at Chosan , 120 miles north of Pyongyang . Communist forces counterattacked within two days along the ROK lines near Chosan , forcing the South Koreans to retreat . The People ' s Republic of China had entered the conflict against the Eighth U . S . Army in Korea in the west , and the U . S . X Corps in the east . At this point , the war in Korea took on an entirely different character as the tide turned against the UN forces .