The night of 25 November 1950, hundreds of thousands of Chinese Communist troops had crossed the Yalu River into North Korea to attack advancing U.N. forces. Hordes of Chinese cut off and surrounded the 5th and 7th Marine Regiments with a human wall at Chosin Reservoir on 27 November. The breaching of this wall and releasing of UN troops depended upon air cover and firepower from planes of carriers stationed off the eastern coast. "McKean", "Hollister" and "Frank Knox" were released from patrolling the Formosa Straits sometime after 8 December. Under a protective canopy of naval air cover, the leathernecks broke through 10 December at Chinhung-ni and moved to Hŭngnam for evacuation. The United States Navy completed the Hŭngnam withdrawal of 24 December after embarking 105,000 troops, 91,000 refugees and vast quantities of military cargo. Needing upkeep, "McKean" first ported at Yokosuka, then to Sasebo until 23 December 1950. She was to rejoin TF 77 on 24 December 1950, Christmas Eve. At that time TF 77 was the largest assembled fleet since World War II, with four carriers, the battleship "Missouri", two cruisers and over 30 destroyers.