In 1862, Jonathan Letterman was appointed medical director (chief surgeon) for the Army of the Potomac. He transformed the U.S. Army’s inadequate medical system. In 1864, Medical reforms based on his system were established throughout the Union army.
Each Federal regiment included one surgeon and one assistant surgeon whose appointments were confirmed by their state’s medical examining board
Surgeons wore the same uniforms as their equal officer
rank in the other branches. Their shoulder straps were green, as
was their sash. Because of this difference, surgeons seemed to keep
their sashes throughout the war even when most officers abandoned theirs.