Marines of 1st Marine Division at the Battle of Chosin Reservoir.
Following the end of World War II and the postwar draw down of forces, by 1950 the division only possessed the strength of a reinforced regimental combat team.[24] The division would be assembled on the battle field and would participate in the amphibious assault at Inchon under the orders of General MacArthur.[25] "The Old Breed" was the unit chosen to lead the Inchon landing on 15 September 1950. At Inchon, the division faced one of its most daunting challenges, deploying so hurriedly it still lacked its third infantry regiment and ordered to execute an amphibious assault in a city the size of Omaha, Nebraska under the worst tidal conditions they had ever faced. After the landing they moved north and after heavy fighting in Seoul they liberated the city.
After the liberation of Seoul, the division was put back on ships and taken to the eastern side of the Korean peninsula and put ashore at Wonsan. As part of X Corps commanded by Army Major General Edward Almond the division was ordered to push north towards the Yalu River as fast as possible.[26] The then commanding officer of the division, Major General O.P. Smith, did not agree with his superiors and had become convinced that they were stretched thin and that the Chinese Forces had entered the war. He purposely slowed his advance and consolidated along the way at every opportunity.[27] The 1st Marine Division was attacked by ten Chinese infantry divisions on 27 November 1950. They fought their way out of the Chosin Reservoir against seven Communist Chinesedivisions suffering over 900 killed and missing, over 3,500 wounded and more than 6,500 non-battle casualties mostly fromfrostbite during the battle. The greater part of the Chinese 9th Army was rendered ineffective as they suffered an estimated 37,500 casualties trying to stop the Marines' march out of the "Frozen Chosin".[28][29]
Beginning in early 1951 the division participated in several UN (UN) offensives in east-central Korea. This was followed by defending against the Chinese spring offensive composed of over 500,000 troops. By June 1951 the 1st Marine Division had pushed northward and secured the terrain around the Punchbowl and then settled into a defensive line 11 miles long.[30]
In mid-March 1952 the 8th Army, to whom the Marines were attached, instituted Operation Mixmaster. The operation was a massive redeployment of UN forces designed to put more South Korean Army units on the Main Line of Resistance (MLR).[31] The 1st Marine Division was reassigned to the far western end of the United Nations line defending a 35-mile line that encompassed the Pyongyang to Seoul corridor. For much of the next year, in what would be termed the "Outpost War", action along this line consisted of small, localized actions because much of the fighting revolved around the holding and retaking of various combat outposts along key pieces of terrain. This changed in March 1953 when the Chinese launched a massive offensive across the U.N. line. The heavy fighting continued until the Armistice took effect on 27 July 1953.[30] During the Korean War the division suffered combat casualties of 4,004 dead and 25,864 wounded.