Chief medical officer

The chief medical officer (CMO), first medical officer or ship's surgeon was a senior staff-level position, typically held by a lieutenant commander or commander who was a doctor of medicine with surgical skills. A nurse could also hold this position if no qualified doctors were available. 

Chief medical officers were also referred to as the "ship's surgeon" in the 23rd and 24th centuries. 

Some noted chief medical officers in Starfleet history were:


 * Doctor Phlox of
 * Doctor Leonard McCoy of the USS Enterprise (NCC-1701) and USS Enterprise (NCC-1701-A)
 * Doctor Beverly Crusher of the USS Enterprise (NCC-1701-D) and the USS Enterprise (NCC-1701-E)
 * Doctor Katherine Pulaski of the USS Enterprise (NCC-1701-D)
 * Doctor Julian Bashir of Deep Space 9 and the USS Defiant (2370)
 * The Doctor, the Emergency Medical Holographic program of the USS Voyager

The Starfleet of the alternate reality established in 2233 by the temporal incursion of the Romulan Nero had one noteworthy chief medical officer:
 * Doctor of the USS Enterprise (NCC-1701 alternate reality) (NCC-1701)

Typical ranks
Chief medical officers have held a variety of ranks. They could hold any rank in the lieutenant grades, but were quite often seen as lieutenant commanders. Chief medical officers were eligible to take the Bridge Officer's Test for promotion to full commander. At this point, they were considered capable of assuming command of a starship. In light of that, their primary duties remained the crew's physical well-being, and 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 were directly in charge of the sickbay or infirmary, commanding medical department personnel and activities. The CMOs' primary duties were the oversight and maintenance of the overall health and physical fitness of crew and passengers. Furthermore as standard medical procedure, the CMO had full medical authority over any patient officially admitted into their care in their facility, including superior officers, until they were formally released from care.

Officers likely to be assigned as the CMO over long-duration missions of exploration had 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. 

Medical authority
In addition to the normal duties of an officer, Starfleet Order 104 Section C gave CMOs the power to relieve an officer or crewman, including a superior one, of their duties if in the CMO's professional judgment, the officer in question was medically unfit. The CMO in question would need to officially certify and provide evidence of unfitness at a subsequent board of inquiry. Typically, the CMO was expected to have the support of a senior command officer or detailed medical documentation to justify this course of action. 

The chief medical officer was able to impose upon crewmembers medical physicals if the mission lasted more than two weeks. 

The CMO also seemed to have the authority to order officers to do things that would be beneficent to their health, like sleeping. 

In the 23rd century, chief medical officers certified the health of research personnel on alien planets on a yearly interval. 

''In an alternate timeline on stardate 51425, The Doctor cited Starfleet Medical Regulation 121, Section A in an attempt to relieve 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.''

Starfleet chief medical officers

 * Dr. Sarah April
 * USS Enterprise (NCC-1701) (2245- before 2254)
 * Dr. Julian Bashir
 * Station Deep Space 9 (2369-)
 * USS Defiant (2370) (2371-2375)
 * USS Defiant (2375) (2375-)
 * Dr. Phil Boyce
 * USS Enterprise (NCC-1701) (2254)
 * Dr. Carter
 * USS Exeter (NCC-1672) (2268)
 * Dr. Christine Chapel
 * USS Enterprise (NCC-1701) (briefly as a nurse in 2269 ; 2270s)
 * Dr. Arthur Coleman
 * Ship unknown
 * Dr. Beverly Crusher
 * USS Enterprise (NCC-1701-D) (2364, 2366-2371)
 * USS Enterprise (NCC-1701-E) (2372-2379)
 * The Doctor
 * USS Voyager (2371-2378)
 * Dr. Elizabeth Lense
 * USS Lexington (NCC-30405) (2371)
 * Dr. Leonard McCoy
 * USS Enterprise (NCC-1701) (2266-2270, 2270s-2285)
 * USS Enterprise (NCC-1701-A) (2286-2293)
 * Dr.
 * USS Intrepid (NCC-38907) (2346)
 * Dr. Phlox
 * (2151-2161)
 * Dr. Mark Piper
 * USS Enterprise (NCC-1701) (2265)
 * Dr. Katherine Pulaski
 * USS Repulse (?-2365)
 * USS Enterprise (NCC-1701-D) (2365)
 * Dr. Martin Rackham
 * USS Strata

Alternate timelines and parallel universes

 * Dr. $𝜇$
 * (2154)
 * Dr. Puri
 * USS Enterprise (NCC-1701 alternate reality) (2258)
 * Dr.
 * USS Enterprise (2258-2263)
 * USS Franklin (2263)
 * USS Enterprise-A (2260s)
 * Dr. $𝜇$
 * (2267)
 * Dr. Alyssa Ogawa
 * USS Enterprise (NCC-1701-D) (2370)

Aliens

 * Banean Chief Medical Officer
 * Vidiian Sodality Chief Surgeon
 * Sulan

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 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
 * USS Excalibur (NCC-26517) in Star Trek: New Frontier
 * Dr. Elizabeth Lense
 * USS da Vinci in Star Trek: Starfleet Corps of Engineers
 * Dr. Carter Greyhorse
 * USS Stargazer in Star Trek: Stargazer
 * Dr. T'Pek
 * USS Destiny in The Lives of Dax
 * Dr. Ree
 * USS Titan in Star Trek: Titan
 * Dr. Jarem Kaz
 * USS Voyager in 
 * Dr. Savel
 * USS Enterprise-F in Star Trek Online