Serving as 57-mm antitank gunner with the 2d Battalion, he was a major factor in stopping enemy tanks during heavy attacks against the battalion position near Dom Butgenbach, Belgium, on 20-21 December 1944. In the first attack, launched early in the morning on the 20th, enemy tanks succeeded in penetrating parts of the line. Cpl. Warner, disregarding the concentrated cannon and machine-gun fire from two tanks bearing down on him and ignoring the imminent danger of being overrun by the infantry moving under tank cover, destroyed the first tank and scored a direct and deadly hit upon the second. A third tank approached to within five yards of his position while he was attempting to clear a jammed breach lock. Jumping from his gun pit, he engaged in a pistol duel with the tank commander standing in the turret, killing him and forcing the tank to withdraw. Following a day and night during which our forces were subjected to constant shelling, mortar barrages, and numerous unsuccessful infantry attacks, the enemy struck in great force on the early morning of the 21st. Seeing a Mark IV tank looming out of the mist and heading toward his position, Cpl. Warner scored a direct hit. Disregarding his injuries, he endeavored to finish the loading and again fire at the tank, whose motor was now aflame, when a second machine-gun burst killed him. Cpl. Warner's gallantry and intrepidity at the risk of life above and beyond the call of duty contributed materially to the successful defense against the enemy attacks.