The 1st Marine Division landed at Wonsan on Korea's east coast in October 1953.  When the 12,000-man division started advancing north it looked like the North Korean Army was defeated and maybe the Marines would all be home by Christmas.  As they got higher into the mountains the weather turned much colder and the Marines started to get some indications the Chinese Army had entered Korea also.  The Marines' suspicions were confirmed when they reached the Chosin reservoir.  They were surrounded by 60,000 Chinese soldiers in the freezing mountains.