It can be militarized during times of war but officers are considered non-combatants unless detailed to serve with a branch of the military. Most serve on Indian reservations.
And other duties also. The US Coast Guard has no medical officers and the role is filled by USPHS officers who wear naval or USCG uniforms and rank. USPHS also provides dental and nursing officers .
I believe the USPHS Commissioned Corps grew out of doctors who performed quarantine exams and credit for merchant seamen who arrived in a port ill.
A goodly number of the officers are also assigned to the Centers for Disease Control in Atlanta. Those are very academic docs. A number of years ago I was sent by Harvards to to Atlanta review a US CDC program that was up for an award. Most I met with were Captains or Rear Admirals.
My last day there I began to feel feverish. Your mind runs amuck when you have been walking past labs with BLS Level 4 security which contain things like Ebolas, Smallpox etc. I asked the Rear Admiral I was meeting with I I could get my temp checked. He immediately ordered an aide to escort me to employee health. I was greeted there by a doctor who greeted me by name. He looked about 19 or 20 but had to be older as his name tag said MD, MS, PhD. I asked and he explained he had a PhD in Virology and an MS in molecular biology. It turned out to be some 24 hour bug
When my wife was an active duty USN Officer I would get medical exams for free air the USCG clinic in Boston and dental work there. The dentists were USPHS officers although the one who did most of my work was an Iranian, Italian educated, dentist who was working for the USCG to get the required time in in a supervised setting to get a US dental license. She was absolutely gorgeous and looked like a young Sophia Loren. She could do whatever she wanted in my mouth as long as I could lie back and look at that beautiful face.