The Joint Chiefs, the Navy, and MacArthur's own staff opposed the Inchon landing. The port had extreme tidal variations—a 32-foot range that exposed mud flats for hours, limiting landing windows. The approaches were dominated by Wolmi-do Island, which had to be secured first, eliminating any surprise. The seawall was too high for standard landing craft. MacArthur overrode all objections and was spectacularly right.

The Landing

Marines landed on Wolmi-do at dawn on September 15 and secured it in 45 minutes. The afternoon tide brought the main landing force against the seawall of Inchon. Marines scaling ladders under fire captured Inchon by evening with surprisingly light casualties. Seoul fell September 27. The supply lines of every North Korean unit south of the 38th Parallel were severed. NKPA forces in the south disintegrated.

The Decision to Cross the 38th Parallel

The success at Inchon created a decision point the UN had not anticipated: what to do with a victorious army standing at the original boundary. MacArthur urged—and was authorized—to cross north and reunify Korea by force. China sent warnings through diplomatic back channels that UN forces crossing the 38th Parallel would bring Chinese intervention. These warnings were systematically discounted by MacArthur's intelligence assessments.

The Price of Hubris

By late October, UN forces were advancing toward the Yalu River. Chinese People's Volunteer Army forces of approximately 300,000 men had crossed in the last weeks of October, concealed by night movement and radio silence. MacArthur's headquarters misread initial Chinese contact engagements as evidence of limited commitment. On November 27, the Chinese offensive struck in full. Inchon had been a masterstroke; the subsequent advance to the Yalu was its undoing.