Inchon and the UN Counter-Offensive
A Plan Almost Everyone Opposed
By August 1950, UN forces clung to the Pusan Perimeter while North Korean armies hammered them from the north. General Douglas MacArthur, the UN Commander, proposed something audacious. Instead of fighting a slow advance back up the peninsula, he would land a fresh army 240km behind enemy lines, at the western port of Inchon. The objective was simple: cut the long, thin North Korean supply lines, isolate their forces around Pusan and recapture Seoul. The plan was so risky that the Joint Chiefs of Staff in Washington tried to talk him out of it.
On 15 September 1950, MacArthur launched Operation Chromite, an amphibious landing at Inchon roughly 240km behind North Korean lines. Seoul was recaptured by 28 September. The success of Inchon transformed the war.
Why Inchon Was So Risky
Inchon’s tides were among the most extreme in the world — 9 metres from low to high. Outside short tidal windows the harbour was an unusable mud-flat. The approach was through narrow channels under the guns of Wolmido Island. There were no beaches; troops had to climb sea walls. MacArthur’s argument was the opposite: the very impossibility of Inchon meant the North Koreans had not defended it.
The Landings Themselves
In the early hours of 15 September the US Navy bombarded Wolmido. Marines from the 1st Marine Division went ashore at the morning high tide and seized the island within hours. The main landing came at the evening high tide; landing craft put X Corps ashore at two beaches, codenamed Red and Blue. Within 24 hours, US X Corps was in Inchon and pushing inland. The next objective was Seoul, only 25km away. Within two weeks, the South Korean capital had been recaptured in heavy block-by-block fighting against North Korean rearguards who fought from house to house with mortars and grenades. On 28 September the Republic of Korea flag flew again over the capital. The political effect was as important as the military one: an attack that had looked unstoppable in July had been broken in six weeks.
Inchon worked because of the Pusan breakout. As MacArthur landed in the west, the UN’s Eighth Army attacked north out of the Pusan Perimeter. North Korean forces were caught between the two. Their supply lines collapsed; whole units surrendered. Of the original North Korean army that had crossed the 38th parallel in June, only around 30,000 made it back to the north intact. The rest were killed, captured or scattered.
From Containment to Rollback
Until Inchon, the war’s objective had been simple: restore the 38th parallel. But UN forces stood at the parallel by 1 October 1950. Should they cross it? Rollback — pushing communism out of the north entirely — offered the chance to reunify Korea under Rhee, end the threat permanently and hand Truman a political victory. The Joint Chiefs in Washington supported a limited advance; Republican critics in Congress demanded the destruction of communism in Korea. On 7 October the UN General Assembly authorised the advance, telling MacArthur to use ‘all appropriate steps’ for ‘a unified, independent and democratic government’ throughout Korea. ROK forces had already crossed; US forces followed on 9 October. The shift from containment to rollback was the most fateful political decision of the war.
Towards the Yalu
The advance into North Korea began as a triumph. Pyongyang fell on 19 October. UN troops captured huge stocks of Soviet weapons and freed thousands of UN prisoners-of-war. By late November some forward units were within sight of the Yalu River, the border with communist China. MacArthur publicly promised the troops would be home by Christmas and authorised some commanders to begin planning unit redeployments back to the United States. He divided his forces into two columns — X Corps on the east coast, Eighth Army on the west — with a wide gap between them in the cold mountainous interior. The split made supply easier but left no mutual support if either column was attacked.
Throughout October Beijing sent increasingly explicit warnings — through Indian diplomats and public statements — that China would not accept hostile forces on the Yalu. Mao genuinely believed UN advance to the Chinese border threatened the new revolution. MacArthur dismissed the warnings as bluff, telling Truman at their Wake Island meeting on 15 October that any Chinese intervention would be ‘the greatest slaughter’. He was wrong on every count.
Between 15 September and late November 1950, UN forces moved from the Pusan Perimeter to Inchon (15 Sept), Seoul (28 Sept), the 38th parallel (1 Oct), Pyongyang (19 Oct), and units in sight of the Yalu (late Nov). Then everything changed.