The battalion was in Yudam-ni on the evening of 27–28 November 1950 when the Battle of Chosin Reservoir began. On the first evening, the Marines of "How Company" were overwhelmed on Hill 1403 by waves of Chinese attackers and were eventually ordered to pull back by the commanding officer (CO), Lieutenant Colonel William Harris The battalion continued to fight on the hills around Yudam-ni for the next few days until 1 December when the 5th Marines and 7th Marines were ordered to fight their way back to the 1st Marine Division’s main perimeter at Hagaru-ri. The 300+ remaining members of 3/7 provided the rearguard for the two regiments as they brokeout to Hagaru-ri and were the last Marines to leave the perimeter at Yudam-ni as it was being overrun by Chinese forces 3/7 consolidated with the rest of the division at Hagaru-ri and took part in the fighting breakout towards Koto-ri where, on 7 December, all of the 1st Marine Division’s regiments were together for the first time since the landing at Wonsan in October Of note during the battle, on the morning before their arrival at the Koto-ri perimeter, the battalion's CO, who during the battle was described as "coming apart" and having an "emotional breakdown and collapse", disappeared and was never seen again. After the withdrawal from Chosin the 1st Marine Division was evacuated from Hungnam.