Through all the long bombardment that followed; until Sumter was reduced, and Wagner and Gregg was ours, amid the scorching sun and the prevalence of prostrating diseases, though herself more than once struck down with illness, she remained at her post, a most fearless and efficient co-worker with the indefatigable agent of the Sanitary Commission, Dr. M. M. Marsh, in saving the lives and promoting the health of the soldiers of the Union army. "How could you," said a friend to her subsequently, "how could you expose your life and health to that deadly heat?" "Why," she answered, evidently without a thought of the heroism of the answer, "the other ladies thought they could not endure the climate, and as I knew somebody must take care of the soldiers, I went."
In January, 1864, Miss Barton returned to the North, and after spending four or five weeks in visiting her friends and recruiting her wasted strength, again took up her position at Washington, and commenced making preparations for the coming campaign which from observation, she was convinced would be the fiercest and most destructive of human life of any of the war. The first week of the campaign found her at the secondary base of the army at Belle Plain, and thence with the great army of the wounded she moved to Fredericksburg. Extensive as had been her preparations, and wide as were the circle of friends who had entrusted to her the means of solace and healing, the slaughter had been so terrific that she found her supplies nearly exhausted, and for the first time during the war was compelled to appeal for further supplies to her friends at the North, expending in the meantime freely, as she had done all along, of her own private means for the succor of the poor wounded soldiers. Moving on to Port Royal, and thence to the James River, she presently became attached to the Army of the James, where General Butler, at the instance of his Chief Medical Director, Surgeon McCormick, acknowledging her past services, and appreciating her abilities, gave her a recognized position, which greatly enhanced her usefulness, and enabled her, with her energetic nature, to contribute as much to the welfare and comfort of the army in that year, as she had been able to do in all her previous connection with it. In January, 1865, she returned to Washington, where she was detained from the front for nearly two months by the illness and death of a brother and nephew, and did not again join the army in the field.