United States Navy enlisted Hospital Corpsman, (HM), who has volunteered to serve with the United States Marine Corps. This does not include the BAS Corpsmen or those who staff base clinics or hospitals. This term of endearment is reserved exclusively for corpsmen who actually cammie up and hump a ruck.
"HM3 Chiarini of 1st Battalion 2nd Marines, 2nd Marine Division was awarded the Silver Star after making 4 trips across a hundred meter, bullet swept battlefield to retrieve his wounded Marines. Oorah, devil doc."