After occupation duty in Japan, he returned to the United States in 1946 to continue his Marine Corps career. As the United States once again found itself at war in 1950, then Captain Barber was sent with the 2nd Battalion, 7th Marines (the "War Dogs", motto "Ready for anything, counting on nothing.") to Korea.
During the Battle of Chosin Reservoir from November 28 to December 2, 1950 in freezing, snowy weather, Captain Barber's company of 220 Marines was assaulted by no fewer than 1,400 communist attackers of the Chinese People's Liberation Army. They were defending the supply line to the rest of the 1st Marine Division; the survival of 8,000 of their comrades depended on their stand. Throughout the fight, the Marines of F Company could count on one thing: the incredible heroism and leadership of their commander.
From Medal of Honor Citations for the Korean War:
BARBER, WILLIAM E.
Rank and organization: Captain U.S. Marine Corps, commanding officer, Company F, 2d Battalion 7th Marines, 1st Marine Division (Rein.). Place and date: Chosin Reservoir area, Korea, 28 November to 2 December 1950. Entered service at: West Liberty, Ky. Born: 30 November 1919, Dehart, Ky. Citation: For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty as commanding officer of Company F in action against enemy aggressor forces. Assigned to defend a 3-mile mountain pass along the division's main supply line and commanding the only route of approach in the march from Yudam-ni to Hagaru-ri, Capt. Barber took position with his battle-weary troops and, before nightfall, had dug in and set up a defense along the frozen, snow-covered hillside. When a force of estimated regimental strength savagely attacked during the night, inflicting heavy casualties and finally surrounding his position following a bitterly fought 7-hour conflict, Capt. Barber, after repulsing the enemy gave assurance that he could hold if supplied by airdrops and requested permission to stand fast when orders were received by radio to fight his way back to a relieving force after 2 reinforcing units had been driven back under fierce resistance in their attempts to reach the isolated troops. Aware that leaving the position would sever contact with the 8,000 marines trapped at Yudam-ni and jeopardize their chances of joining the 3,000 more awaiting their arrival in Hagaru-ri for the continued drive to the sea, he chose to risk loss of his command rather than sacrifice more men if the enemy seized control and forced a renewed battle to regain the position, or abandon his many wounded who were unable to walk. Although severely wounded in the leg in the early morning of the 29th, Capt. Barber continued to maintain personal control, often moving up and down the lines on a stretcher to direct the defense and consistently encouraging and inspiring his men to supreme efforts despite the staggering opposition. Waging desperate battle throughout 5 days and 6 nights of repeated onslaughts launched by the fanatical aggressors, he and his heroic command accounted for approximately 1,000 enemy dead in this epic stand in bitter subzero weather, and when the company was relieved only 82 of his original 220 men were able to walk away from the position so valiantly defended against insuperable odds. His profound faith and courage, great personal valor, and unwavering fortitude were decisive factors in the successful withdrawal of the division from the deathtrap in the Chosin Reservoir sector and reflect the highest credit upon Capt. Barber, his intrepid officers and men, and the U.S. Naval Service.