Temperatures dropped to minus 35–40 Fahrenheit at the reservoir. Oil froze in weapons. Morphine syrettes had to be thawed in soldiers' mouths before injection. Blood plasma couldn't be given intravenously because it would freeze in the tubes. The Chinese attackers, many without adequate cold weather gear, froze in position during night attacks and were found still gripping their weapons in the morning.

The Encirclement

The 1st Marine Division and attached Army units were positioned around the Chosin Reservoir when the Chinese 9th Army Group—12 divisions, approximately 120,000 men—attacked simultaneously from multiple directions. Task Force Faith on the eastern shore—3,200 Army troops—was overrun over three days, with approximately 950 survivors reaching Marine lines. The main Marine body at Hagaru-ri held their perimeter.

The Breakout

Marine General Oliver Smith's famous response to the word 'retreat': 'Retreat, hell! We're just attacking in a different direction.' Smith had anticipated encirclement and spent weeks prior stockpiling supplies and building an emergency airstrip despite pressure to advance. When the breakout south began on December 1, Marines fought through Chinese roadblocks in intense cold while the new airstrip evacuated 4,500 wounded.

At Funchilin Pass, a critical bridge had been destroyed. USAF C-119s air-dropped bridge sections that Marine engineers assembled under fire. The division crossed and reached Hungnam harbor by December 11, having brought their dead, their wounded, and most of their equipment. Chinese casualties at Chosin: estimated 25,000 killed, 12,500 wounded, thousands more frozen to death.