Colonel James P. McMahon took command of the 164th New York Volunteer Infantry in 1863. James led the 164th until his death in the battle of Cold Harbor, June 3, 1864. Early that morning, his regiment was ordered forward against the entrenched Confederate Third Corps. The Army and Navy Journal reported on his death: “Leading his men to assault the enemy’s works he daringly dashed ahead, and foremost, fighting with the National colors in one hand, was in the act of planting them upon the earthworks which entrenched the foe, when his body was pierced with six bullets by the Rebel sharpshooters.”
The Battle of Cold Harbor was a clear loss for the Union. On June 3 alone, the Union suffered more than four times as many casualties as it inflicted without seriously breaching the Confederate fortifications.
McMahon left no widow and had no children, but he helped support his teenage sister, who applied to receive a pension as a dependent orphan. Her pension application can be viewed on Fold3.