We all know that Spock is second in command, but who comes after that?

I ask because last night I re-watched Shore Leave, which featured Kirk, Sulu, and McCoy being sent to investigate a new planet. They communicate to the ship that something strange is happening and Spock beams down. I thought Sulu was third in command, after Spock. If so, the top-three-ranking officers are all on a mysterious planet and (apparently) in mortal danger. This seems like it should be a severe breach in protocol. If things go horribly wrong, who's in command?

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    This is the same question I ask every time the main cast of a Star Trek episode, all of them at the top of the Chain of Command, personally go down to investigate anomalies on an away mission.
    – Zibbobz
    Commented Apr 24, 2014 at 17:46
  • It seems as though in Starfleet there are 3 criteria for who is to be put in command: (1) rank (generally outweighs all other considerations), (2) command qualification (given 2 or more candidates of equal rank), and (3) discretion of the delegating officer (based on personal assessment of the candidate's experience in the situation).
    – Anthony X
    Commented Jan 3, 2021 at 18:35

9 Answers 9


If we were to use this image below as a reference for the Original Series Star Trek Crew, the command structure would be:

enter image description here

Bridge Officers

  • Captain - James T. Kirk, Ship's Captain
  • Lt. Commander - Spock, First Officer, Science Officer
  • Lieutenant - Hikaru Sulu, Helmsman, Navigation Officer
  • Lieutenant - Nyota Uhura, Communications Officer
  • Ensign - Pavel Checkov - Helmsman, Weapons Officer

This would be the order of command in the event of an emergency with only the bridge crew available. However, we are often left with Lt Commander, Montgomery Scott, who despite being in Engineering most of the time, is still considered, the Second Officer and in charge of the ship since he outranks all of the bridge crew except for Mr. Spock. His experience in combat may also be superior because of his time in Starfleet.

Non-Bridge Crew

  • Lt. Commander - Montgomery Scott - Chief Engineer, Second Officer

  • Lt. Commander - Leonard McCoy - Ship's Lead Doctor

  • Enlisted Nurse - Christine Chapel - Lead Nurse

  • Dr. McCoy and Nurse Chapel are the only members of this image who would never be left in a command role unless there were NO other living officers on board the ship available. While the Doctor has respectable rank, he has no experience in command and no desire for the training to become a command officer.

  • Ranking officers who are capable of being in command of the Enterprise may, from time to time be placed in command of the ship in lieu of regular ship officers due to their experience or political power in the Federation.

As far as landing parties go, it was the Captain's prerogative to go on Landing Parties but Spock was very fond of citing regulations against the entire command structure going on hostile missions on the surface of alien planets. Kirk always chose to go anyway.

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    Just one small point, as you noted Nurse Chapel is an Enlisted person and would NEVER be allowed to take command of a star ship regardless of if there where no other higher ranking personnel on board.
    – Monty129
    Commented Jun 13, 2013 at 22:08
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    It falls to the rank structure first, or by who is designated by the proper authority. If Kirk leaves the ship with Spock and Scotty and designates Sulu to be in charge then Sulu IS in charge. If Sulu is hurt and Uhura is on the bridge, then she is in charge as the next ranking officer. Ranking duty officer on the bridge is who is in charge. If Sulu is asleep and leaves the duty officer, an unknown Ensign, during an emergency he is in charge until Sulu retakes the bridge as the duly designated representative or until a senior ranking officer arrives and takes command. Commented Jun 13, 2013 at 22:30
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    Is any of this backed up by references, or just speculation? Commented Jun 14, 2013 at 16:50
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    There is a really good TOS novel by Diane Duane (just love her work) called "Doctor's Orders" in which Kirk, on a whim, leaves McCoy in command while he goes down to shore leave and then seemingly disappears (being captured by aliens). And because the Captain left him in command, and McCoy IS command rank, no one, not even Spock, can relieve him. It leads to an amusing story about Dr.McCoy trying to deal with Klingons and space battles from the command chair and freaking out about it. Go read it. Commented Jun 14, 2013 at 19:13
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    Chapel is an ensign, not enlisted. O1. In TMP, she's a LCdr. However, Medical officers are usually Staff Officers, not Line officers- You work down the Line officers first, then down the staff, then finally, into the enlisted. LCdr McCoy would take command well after Ens Checkov, because Checkov is a line officer, and McCoy is a staff officer. Uhura may be a staff officer; it's not specified, and we never see her take the conn in TOS. Likewise, we don't know if all the redshirts are line or staff; it's highly likely, given that LCdr Giotto doesn't take command, and sulu does, that sec'ty=staff
    – aramis
    Commented Jun 17, 2013 at 12:36

The Pilot, Where No Man Has Gone Before, has several lieutenant commanders (LCdr) on board. There is no clear distinction.

However, it's been customarily assumed that Mr. Mitchell was the first officer until his death.

In the run of the series, we see the following LCdr ranked personell: Gary Mitchell (C.Helm), Spock (C.Sci), Scott (C.Engr), McCoy (C.M.O), Giotto (C.Sec), Finney (C.Rec.).

We know that, after episode 1, Spock is the executive officer as well as Chief Science Officer;

Making Sense of things.

It is important, however, to understand several elements of "Naval Tradition" to make sense of things.

Line of Command vs Chain of Command

The Chain of Command differs for almost everyone aboard - only the Commanding Officer, Vice Commander, and Executive Officer are in everyone else's. Chain of command is "Who do I get orders from, and to whom do I give orders?" - Unless you're the captain, someone is above you aboard.

The Line of Command is who takes over when. It's not as simple as just rank - rank figures, but isn't the sum total. Note that the term is now fairly archaic; it's not used much, and modern military use conflates it with Chain of Command, but conceptually, they are different, so I will use the archaism for clarity.

Line vs Staff

Navies have almost always distinguished officers into two or three broad groups: Line Officers, Restricted Line Officers, and Staff Officers.

Line officers are trained for ship command; part of their training includes how to Conn a ship, and how to handle a large number of administrative and tactical functions.

Restricted Line are usually aviators or engineers. Many navies don't use this category; some did, but don't any more. Restricted line officers can have positional line-of-command, but if they don't they come after the unrestricted line officers. For certain eras, Gunnery Officers might be Restricted Line,

Staff Officers are persons given officer rank for purposes of authority, but who are not in the line of command.

We can strongly infer a Line vs Staff distinction in TOS/TAS, and it's pretty clear; we cannot make a clear case for Restricted Line officers, but there is a weak inference.

Positional Authority

The Line of Command is traditionally Commanding Officer, Vice Commander, Executive Officer, Chief Operations officer, Chief Engineer. Vice Commander is not often used on ships; it's common for higher commands. First Officer may be either the Vice Commander (if there is one) or the Executive Officer.

The normal for ships, and due to TOS dialogue, we know that it's the case for TOS, is an Executive Officer as First Officer, since Kirk uses both terms for Spock.

Chief of Operations would be the seniormost officer Helmsman or Navigator. Chief Engineer is the Seniormost Engineer.

We do not know which was first officer during the Pilot Episode - It could be Mitchell or Spock. Given that Mitchell is in a position in the line of command already, and in command division, we can make a reasonable but weak inference that it's likely Mitchell, and the prior Exec either was transferred or killed prior.

A Captain normally has a Commander (CDR) for an Executive officer. We do not see a full commander until Scott and Spock are promoted to that grade.

Conn vs Command

The Conn officer is the officer in operational control of the vessel for a given watch. Conn officers may or may not be in the line of command - many line officers get an occasional shift as the Conn. It doesn't mean they are in the line of command.

Any time the senior watchstander has to leave the bridge, he should (and in TOS, we see them do so) tell someone else they have the Conn. We see a number of Lieutenants take the conn. But we never see Uhura take the Conn.

Authority vs Command

Within their area of competence, a staff officer can give orders, and expect them to be followed. Certain officers can give orders to their superiors even - CMO and Chief Psychiatrist within their professional capacity, JAG/Legal on matters of law. Doing so is a touchy issue - it can make or break careers.

The evidence for Line vs Staff

We have three ranking LCdr types who neither take the Conn nor take command: McCoy, Giotto and Finney.

McCoy is the CMO - as a doctor, he's probably not trained for Conn duty, and his routine duties take most of his time.

Giotto is the Chief of Security. Again, his duties probably do not require him to be trained in commanding the ship.

Likewise, Finney is a line officer; we know his training was as a line officer. But he's assigned into a position that is a staff-type position, and never takes the Conn. (Reality - Guest Star.) So we can argue that he's been removed from the Line Officer category. Since he's still in green, we can weakly infer he might be restricted line - taken out of the primary line of command, but not prevented from taking conn watches.

Further, there is Uhura. Uhura does not take the conn, and has a replacement to hand the few times she's taken on away missions. It is thus a fair inference that she's a staff officer.

Science and Medical would normally be staff. Security would be staff, tho' not all the guys on Guard details are full time security - some are also rated in other fields.

So, who goes where?

We will assume, for now, no restricted line, and that Finney was right after the "top four." Sulu goes after Scott because Scott's got more experience, and it's implied he's a line officer as well. Some flexibility happens when a senior engineer is faced with a Junior Ops.

We will also assume that, excepting those Ops personell who cross trained into engineering, the other Engineering lieutenants and ensigns we see are staff officers.

The Line of Command

CO: Capt. Kirk
XO: during the pilot, either LCdr Mitchell or LCdr Spock; after, Cdr Spock
C. Ops: LCdr Mitchell
C. Engineer: LCdr Scott
C. Ops: Lt. Sulu †

Line, rows by seniority; alpha within row: LCdr Finney
Lt. Kelso
Lts. Bailey, Farrell, Leslie, Riley, Stiles
Lts. DePaul, DeSalle, Hansen, Hadley, Painter, Spinelli
Lts. Kyle, Rahda
Ens. Chekov, Haines

Staff Officers

C. Sci: LCdr Spock
C. Records: LCdr Finney (after science because it is an exploration vessel)
C Security: LCdr Giotto
C. M. O.: LCdr Dr. McCoy
C. Psych: Lt Dehner
C. Comm: Lt Uhura
(assorted Sciences,Engineering, and Support Services Lieutenants)
M.O.: Dr. M'Benga (presumably a Lt.)
(Assorted LtJGs in Sciences, Engineering and Support Services)
(Assorted Ensigns)
M.O.: Ens Nurse Chapel

Other commentary

17 operations officers are listed. We know there are three bridges, and 3 shifts, and 2-3 seats for Ops persons in each: Conn, Helm, Nav. And the Conn officer might not even be present in the Emegency or auxiliary; the CO, XO, and someone else rotate the Conn on the main bridge. So, that leaves room for 24 operations types, and a minimum of 18. We know most of the department.

We don't know most of the engineers.

We do see a lot of security guards, but most don't have names. Security are likely staff officers, tho' we see a couple line officers "slumming" in security. (Reality - recycled extras.)

Most of the Science officers are likely staff officers. A few might be in the line, and some line officers do a good bit of science - Sulu is rated in Astrophysics and xenobiology...

We do see some mobility into/out-of the line.

We know that the line/staff distinction is canonical for Trek - it's the focus of an Episode of TNG, as Troi becomes a qualified watch officer (and thus line officer). Again, no specifics of restricted vs unrestricted, but since Crusher ranks several others who do take over, the inference to make is that there is a restricted line distinction.

Generally, within non-line officers, Engineers would tend, historically, to be the priority within a rank, then gunners, then admin, then last, medical. Given that Sciences are a priority, and Roddenberry's insistence that there were no enlisted, as with NOAA's commissioned corps, we'll put non-line sciences at the top of the pile. So, once you're out of line Ensigns, you go to the Staff Commanders, then Lieutenant Commanders, then lieutenants, then Lieutennants Junior grade (and yes, there is photographic evidence for them), then Ensigns. Within each rank, Sciences, then engineers, then security, then other support services, then medical. Within each department, whoever had the rank longest gets it first. Chapel is probably the 2nd to last officer - we see another unnamed nurse in at least one episode. Memory Beta has Hinch and West as additional nurses.

  • Somewhat perplexing is what occurs in TOS: "The Menagerie" Part 1... Spock turns operational command over to Lt. Hansen (on helm duty up to that moment), but presents himself to McCoy (as senior officer present) for arrest.
    – Anthony X
    Commented Jan 3, 2021 at 18:21
  • Nothing perplexing at all - He's submitting himself for an insanity hold. McCoy could have (had he not deceived Spock) held Spock for being mentally unfit for duty; he's just presenting himself to the one person who can directly remove his ability to hold command.
    – aramis
    Commented Feb 3, 2021 at 7:50

As a navy veteran and a Star Trek fanatic I can provide some insight here. Most of what is said is on the right course but I want to clarify with examples....

Rank, position, types of line officer

First and foremost Positional Authority out seats Rank, however when positional can not be established Rank has precedence.

  • Kirk: Captain (Captain)
  • Spock: First Officer/Science Officer (Commander)

Everyone had a job and a rank. Sulu usually was next regarding position however he was not the most senior, in fact Scotty was next by rank among line officers, and McCoy was by overall rank. The term Conn usually who commands the bridge..... on a navy ship we had a OOD (Officer of the deck) who was in command when CO and XO were not on the bridge and the conn was second but usually commanded over the helm which was manned by enlisted. OOD and Conn should be positions of unrestricted line officers from varies departments, usually department heads.

Now there was also a Tactical Action Officer or TAO, Star Trek doesn't use it but the best equivalent would be a science department head in Astrometrics watching a tactical screen. The TAO could assert authority of the OOD if they could determine a tactical threat to the ship, But in the Star Trek world and all sensors tied to the bridge there is no need for a TAO and the TAO and OOD and Conn are one in the same, titled CONN.

If Scotty was qualified OOD and had a reason to he could assert command over Sulu as Conn in the Star Trek world, but likely wouldn't without a damn good reason.

I firmly believe Uhura was a qualified line officer but yes this was filmed in the 60's.

At one point Admiral Jehrico asserted his command and took command from Captain Picard, again a rare thing and in my opinion rude, but rank has privilege its just highly unorthodox to abuse it.

Medical usually comes from Medical corps and are not trained as line officers, however in Beverly Crushers case there wasnt anyone left to command a ship, or she commanded a medical ship or she was commanding a medical mission.

  1. Picard
  2. Riker
  3. Data

On the navy ship I served on this would be CO, XO, and OPS. The positional authority could also be trickled down through department heads and not necessarily directly by rank. you can have a LT command a ship over a LTcdr, if say the LT held Ops deptartment head and the LTcdr was Combat systems (or in this case science), but I don't think anyone would challenge Data even if they had the rank to do so, Troi being a Commander but was not qualified to command, however even after she was qualified Ltcmdr Data was still the Operations officer and Second Officer aboard USS Enterprise D and E, She yielded her rank for his position.

  • Captain Jellico was given command of the Enterprise by Starfeet Command since Captain Picard was reassigned to a covert-ops mission for the episodes Chain of Command (parts 1 and 2). There's no mention of an Admiral Jehrico that I can find. Admiral Pressman does cause some trouble for Picard, but that's mainly because he's using the Enterprise on a "top-secret" (illegal) mission.
    – Ellesedil
    Commented Nov 6, 2015 at 0:04
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    Good additional background on your answer and well-written. I wanted to give this new user some props as many newbies have a hard time getting rep points at first. This can be a tough crowd at times.
    – iMerchant
    Commented Mar 21, 2016 at 1:31
  • One MAJOR flaw - TNG is 70 years after Kirk's Enterprise. Comparing that to the USN or the UK RN, the methods and distinctions of officers from 1910 to 1980, we see drastic changes in what qualifies as a line officer... in a similar span, we can expect changes. Especially since we know multiple wars intervene in both cases - and each war in our History has changed the line-staff relationships (as to who is line, who's restricted line, who's pure staff)... in the 1880's, the USN staff officers were all warrants...
    – aramis
    Commented Jun 15, 2016 at 4:22

S1E 22 - "The Return of the Archons"

Kirk, Spock and Doc are on the planet investing, Sulu was in a trance and presumably out of commission. Here is a quote from 24 minutes 59 seconds into the episode:

"Captain's log star date 3157.4 - The Enterprise, still under attack by some sort of heat rays from the surface of beta 3, is now being commanded by Engineering Officer Scott."

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    This does not provide any information that is not in the accepted answer.
    – Blackwood
    Commented Feb 14, 2017 at 1:01

The Chief medical officer can relieve a captain of duty and assume command of the ship if need be superseding the chain of command. Starfleet's only distinction is between officers and enlisted personnel. Beverly took the command test to become a full commander that means she is qualified to command the ship, this would go for counselor/commander Troi as she also passed the test. They yield their rank to assigned positions but under Starfleet regulations they can assume command if they feel it necessary. On the original series I think Scotty commanded the ship more than any other character besides Kirk and Spock. its worth noting that Nyota Uhura is fifth in command Kirk, Spock, Scotty, Sulu, Uhura, Checkov (Though as a Tactical/command track officer he does get more time in the chair to train him up.) She takes command in two episodes which are considered canon as they include the original cast. (The "Lorelei signal" and "Bem") as well as several books.

  • This is a nice answer but could be backed up by editing in some quotes/evidence? For example, to prove they can assume command of the ship if need be etc.
    – TheLethalCarrot
    Commented Jan 23, 2019 at 15:25
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    Note that in TOS (The Doomsday Machine), McCoy had the authority to relieve Decker (assuming he had supporting medical evidence that Decker was unfit), but he would not assume command in doing so; operational command would fall to Spock.
    – Anthony X
    Commented Jan 3, 2021 at 18:27

In "catspaw" mr desalle was left in command, in "errand of mercy" sulu was left in command as it was a war situation. As i see it kirk likes to give various officers "time in the chair".


I think you guys are forgetting about Scotty. Being a long time fan of the original series, I've seen in many episodes that it appears as though each time Kirk and Spock leave the bridge and particularly when there is a crisis and neither is on the bridge, Scotty is the one in charge...

  • Pretty much every answer above yours mentions Mr Scott.
    – Valorum
    Commented Feb 26, 2019 at 0:01

I once took a trivia quiz on Star Trek TOS, and the question was asked;

"Who is second in command on the Enterprise." The correct answer given was DR. Mccoy because he outranks Mr. Spok.

If the question were who is the second highest ranking officer, that would have been correct as I believe the Doctor was a full commander and Spok was a Lieutenant Commander, However understanding rank structure as I do (Ex-Navy petty officer) I also understand that Dr. Mccoy was not a line officer, and therefore not in line for command unless there simply were no other line officers available. I wanted to point that out to the publishers of the book but there was no email back then and writing letters was too much of a pain... LOL


I agree with the chain of command about the USS Enterprise with Kirk, but the actual chain of command that was in practice is the following:

Captain James T. Kirk, Commanding Officer
Commander Spock, First And Science Officer
Commander Montgomery Scott, Chief Engineer
Lieutenant Sulu, Helmsman
Lieutenant LaSalle, Assistant Chief Engineer

Although Uhura was a Lieutenant, she never took command of the USS Enterprise in any of the episodes for two reasons. The first reason was that she was a woman. The second reason was that she was black. At the time, people were not ready for a woman to take command at all, let alone a black person. The fact that a black woman was in the show may have irked many people during those days. I had thought she did, but she never did.

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