How did Marine artillery and air strikes help defend the positions at Yudam-ni and Hagaru-ri?

During the Battle of the Chosin Reservoir, Marine artillery and air support were essential to the survival and movement of the 1st Marine Division as they fought to consolidate their forces at Hagaru-ri and eventually break out to the coast.1

• Artillery Support: Two Marine artillery battalions moved by bounds during the withdrawal, ensuring continuous fire support for the troops. This artillery was critical in breaking up Chinese ambushes and protecting the vehicle train as units moved from Yudam-ni to Hagaru-ri.1
• Air Support: Marine and Navy fighter-bombers were on call during daylight hours to strike suspected enemy ambushes. Furthermore, the airfield established at Hagaru-ri—protected by the arrival of the 5th and 7th Marines—allowed transport aircraft to deliver vital ammunition and gasoline while evacuating thousands of wounded and frozen casualties.1

This combined firepower and logistical support allowed the Marines to maintain their cohesion, render multiple Chinese divisions ineffective, and successfully execute their "attack in a different direction" toward the port of Hŭngnam.1