The Navy rank of HM3 stands for Hospital Corpsman, Third Class. A Corpsman is a medical specialist enlisted in the United States Navy.
Naval Hospital Corpsmen serve both the Marine Corps and the Navy both on land and aboard ships.
Naval medical history has a long history, with the first written mention of the organization of Navy medicine found in a 1775 document, the Rules for the Regulation of the Navy of the United Colonies of North America, which very briefly described establishing a separate area for the care of the sick and injured.
During World War 2, women were admitted to the Hospital Corps and given the title of WAVES.