The 3rd US Division advanced northward from Wonsan as the UN and South Korean forces near the Chosin Reservoir were in a predicament.
This brought about security problems in Wonsan and they lost Wonsan and the adjacent area south of the city to the enemy.
Thus, the 10th US Army Corps and the 1st Korean Army Corps had to withdraw to the sea as their retreat path was blocked.
The first unit that withdrew from Hungnam was the 3rd Korean Division, and then, the 1st US Marine Division evacuated from the area.
While the evacuation continued, the communist forces took on the fierce offensive.
The UN and South Korean forces fought against the enemy taking into account that it would be difficult to secure a bridgehead unless they dominate the enemy at the beginning.
The Hungnam evacuation operation was a large-scale joint operation of the Army, Navy and Air Force.
Due to the success in the operation, the UN and South Korean forces were able to maintain their combat power and carry on the next phase of operations.