The U.S. Army had no female surgeons, and at first, she was only allowed to practice as a nurse. She was denied a commission as a medical officer, but served anyway as an unpaid volunteer surgeon at the U.S. Patient Office Hospital in Washington and at the First Battle of Bull Run, July 21, 1861. She worked as an unpaid field surgeon near the front lines at Fredericksburg and Chattanooga in 1862. In 1863, Walker was the first female surgeon of the Union Army. During her service, she frequently crossed battle lines, and treated civilians. In September 1862, she wrote to the War Department requesting employment as a spy, but she was