After returning to the United States, he became chief librarian of the Army Medical Library, a position he held for twelve years.

[1][2] McCaw came from a family long prominent in the medical field; his father operated a military hospital for the Confederate States Army during the American Civil War.

[2] After the war, the elder McCaw served as a professor at the Medical College of Virginia, dean of the faculty, and president of the board of visitors.

[2] McCaw demonstrated above average academic ability from an early age, and was educated by private tutors in anticipation of entering medical school.

[16] In February 1898, McCaw was a member of a board of medical officers assigned to Fort McPherson to examine candidates for appointment to the United States Military Academy.

[2] McCaw contracted yellow fever while serving in Cuba and was sent to the army hospital at Montauk, New York, to recuperate.

[4] After his tour of duty in and around Manila, in January 1902, McCaw returned to the United States and was assigned as surgeon at Fort Wadsworth, New York.

[2] After his return to the United States, McCaw was assigned as chief surgeon of the Eighth Corps Area at Fort Sam Houston, Texas.

[2] He served until the end of the war and assisted Ireland in creating and implementing plans for medical support during combat and hygiene for front line soldiers.

[2] McCaw remained in this post during the post-war Occupation of the Rhineland, and was nominated for promotion to brigadier general in December 1918.

Colonel McCaw's counsel and advice in the early stages of the operations of the American Expeditionary Forces were of particular benefit to the effective work of the Medical Department.

As Chief Surgeon of the American Expeditionary Forces, in the later operations in the field, he maintained the splendid efficiency of that department at a critical time and solved each new problem presented with wisdom and marked ability.

[2] McCaw was a Fellow of the American College of Surgeons and an associate fellow of the College of Physicians of Philadelphia[1] He was also an honorary member of the Royal Society of Medicine and the Society of the Cincinnati[1] After his service in Cuba, McCaw became a veteran companion of the Military Order of Foreign Wars and a member of the Military Order of the Carabao.

[30] McCaw hospital closed in 1945, and two of its buildings were moved across the street to what is now the Jonathan M. Wainwright Memorial Veterans Affairs Medical Center.

[32] In 2020, the VCU Committee on Commemoration and Memorials recommended removing, renaming, or de-commemoration of plaques, buildings, portraits, and other memorabilia associated with support of the Confederacy during the Civil War.