Medical Officer

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. A medical officer is usually assigned to work under the asupervision of the CMO and customarily holds the lank of lieutenant or lieutenant junior grade.

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")

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.

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")

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")