The tides at Inchon vary up to 32 feet between high and low. At low tide, the harbour approach becomes an impassable mudflat. The seawalls surrounding the city rise 15 feet. There is no beach. It is, in the assessment of the Joint Chiefs of Staff, almost certainly the worst possible location for an amphibious assault.

Douglas MacArthur chose it deliberately.

The Strategic Situation

By September 1950, the Korean War had been running for two months and was close to lost. North Korean forces had driven the South Korean and United Nations forces to a small perimeter around Pusan. MacArthur wanted a deep amphibious landing far behind enemy lines to cut North Korean supply routes and force a general collapse.

Navy and Marine Corps planners objected: the tidal window was approximately six hours at high tide. The assault window fell in the late afternoon, meaning some waves would land at night. MacArthur overruled them. The very difficulty of the landing was its strength — the North Koreans would not defend Inchon heavily because they would not expect an attack there.

The Assault

September 15, 1950. The 3rd Battalion, 5th Marines seized Wolmi-do, an island controlling the harbour approach, in the morning high tide. In the afternoon, the main assault went in. Marines carried scaling ladders to climb the seawalls of Inchon under fire.

The defenders were caught unprepared. North Korean forces at Inchon numbered approximately 2,000 — too few to mount effective defence against a full Marine division. By nightfall, a beachhead was established. By September 16, the port was secured.

The Exploitation

Seoul, 25 miles east, was retaken by September 28. The strategic effect was precisely what MacArthur had envisioned: North Korean forces at Pusan found their supply lines cut and UN forces appearing behind them. North Korean units attempting to retreat north found main road corridors interdicted. The North Korean People's Army effectively disintegrated.

The Consequences

Operation Chromite was a remarkable operational success. Marine losses in the Inchon-Seoul campaign totalled approximately 364 killed and 1,963 wounded.

What followed was the decision to push beyond the 38th Parallel into North Korea — a choice that brought the People's Republic of China into the war in October 1950, reversing the military situation entirely. The gamble on the tide worked. The gamble on China's intentions did not.