The chief medical officer is a senior staff-level position, typically held by a lieutenant commander or commander who is a Doctor of Medicine with surgical skills.
Chief medical officers were also referred to as the "ship's surgeon" in the 23rd century. (Star Trek VI: The Undiscovered Country)
Typical ranks
Chief medical officers have been seen with a variety of ranks. They can hold any rank in the lieutenant grades, but are quite often seen as lieutenant commanders. Chief medical officers are eligible to take the Bridge Officer's Test for promotion to full commander. At this point, they are considered capable of assuming command of a starship. (TNG: "Thine Own Self") Though in light of that their primary duties are the crew's physical well-being, several Chief medical officers have been civilians with no clear role in the ship's chain of command outside their medical duties. (VOY, ENT)
Specific duties
CMOs aboard a starship or starbase are directly in charge of the sickbay or infirmary, commanding medical department personnel and activities. The CMOs' primary duties are the oversight and maintenance of the overall health and physical fitness of crew and passengers. Furthermore as standard medical procedure, the CMO has full medical authority over any patient officially admitted into their care in their facility, including superior officers, until they are formally released from care.
Officers likely to be assigned as the CMO over long-duration missions of exploration, have scientific training in disciplines outside of medicine, allowing them to take on major, extended research projects; or to better participate in a wider variety of encounters. (TOS: "The Immunity Syndrome"; TNG: "Clues", "Suspicions")
Medical authority
In addition to the normal duties of an officer, the CMO also has the power to relieve an officer or crewman, including a superior one, of their duties if in the officer's professional judgment, he or she is medically unfit. Typically, the CMO is expected to have the support of a senior command officer or detailed medical documentation to justify this course of action. (TOS: "The Doomsday Machine"; TNG: "Lonely Among Us"; VOY: "Year of Hell, Part II")
The CMO does also seem to have the authority to order officers to do things that would be beneficent to their health, like sleeping. (TNG: "Violations")
On stardate 51425 – in an alternate timeline – The Doctor cited Starfleet Medical Regulation 121, Section A in an attempt to relieve Captain Kathryn Janeway of her command. She refused his order, stating that he had no way to actually "implement this protocol". He countered, by saying that he would note the incident in his official log, and that it could lead to her general court martial. (VOY: "Year of Hell, Part II")
Starfleet CMOs
- Dr. Sarah April
- USS Enterprise (2245- before 2254)
- Dr. Julian Bashir
- Station Deep Space 9 (2369-)
- USS Defiant (NX-74205) (2371-2375)
- USS Defiant (NCC-75633) (2375-)
- Dr. Philip Boyce
- Dr. Carter
- Dr. Christine Chapel
- Dr. Arthur Coleman
- Ship unknown
- Dr. Beverly Crusher
- The Doctor
- Dr. Frame
- Dr. Elizabeth Lense
- USS Lexington (2371)
- Dr. Leonard McCoy
- Dr. Phlox
- Dr. Mark Piper
- Dr. Katherine Pulaski
- USS Repulse (?-2365)
- USS Enterprise-D (2365)
- Dr. Martin Rackham
Alternate timelines and parallel universes
- Dr. Phlox
- Dr. Puri
- Dr. Leonard McCoy
- USS Enterprise (2258)
- Dr. Leonard McCoy
- Dr. Alyssa Ogawa
Aliens
- Banean Chief Medical Officer
- Vidiian Sodality Chief Surgeon
Apocrypha
- Decipher's Customizable Card Game states that the ill-fated lieutenant commander who was chief medical officer of the USS Voyager was named Fitzgerald. The novelization of VOY: "Caretaker" also listed him as Fitzgerald.
- There have been several other chief medical officers of note in non-canon Star Trek stories, such as novels and comics:
- Dr. Selar
- Dr. Elizabeth Lense
- USS da Vinci in Star Trek: Starfleet Corps of Engineers
- Dr. Carter Greyhorse
- Dr. T'Pek
- Dr. Ree