The chain of command or command structure was a ranking system used by militaries and other organized groups. It represented the line of authority down which orders are passed from one officer to another, and also the line down which passed command of a particular vessel or installation.
Hierarchy
The chain of command could refer to Starfleet, in general, with the chain beginning with the admiral. The Federation Council, and/or the President of the Federation, could be considered to be at the ultimate top of the chain. (Star Trek IV: The Voyage Home; Star Trek VI: The Undiscovered Country; DS9: "Homefront", "Paradise Lost")
Aboard a starship or most starbases the chain of command began with the assigned commanding officer, usually an officer of the rank of captain, or in some cases commander. This aspect of the command chain functioned similarly aboard a starbase, or space station, as well as in a planetary installation. One example was when Benjamin Sisko was promoted to commander of the station Terok Nor, later named Deep Space 9. (DS9: "Emissary")
If the commanding officer, for any reason, was unavailable to command his or her post then those responsibilities passed down the "chain" to the first officer, then the second officer, etc.
One example of this was when Lieutenant Commander Jean-Luc Picard served as a bridge officer of the USS Stargazer. When the ship's captain was killed and the first officer injured on the bridge, Picard took command of the situation and the vessel. (TNG: "Tapestry")
Obligations and responsibilities
A captain or commander took care of his/her ship or starbase, reviewing different documents like intelligence reports, ship status reports, fuel consumption report, captain's or commander's logs, and other communications. (Star Trek: The Original Series) (citation needed • edit)
One example of this was when In 2267, Yeoman Atkins presented a fuel consumption report to Captain Kirk for his signature. As Kirk was suffering from an exotic disease which caused rapid aging both physically and mentally, Kirk moments later asked Atkins for the report, having forgotten that he had already signed it. (TOS: "The Deadly Years")
Other responsibilities of the captain or commander was to keep informed of crew issues, such as promotion lists, transfer requests, formal reprimands, etc. One example of this was when in 2367, Worf was given a reprimand by Captain Jean-Luc Picard for his killing of Duras which, while legal under Klingon law, was improper conduct for a Starfleet officer. (TNG: "Reunion")
Another example was when in 2375, Captain Kathryn Janeway put a formal reprimand in Ensign Harry Kim's record after he had a sexual relationship with Derran Tal. (VOY: "The Disease")
Officers
Between the launch of Enterprise NX-01 and the late 23rd century, the position of first officer, or executive officer (abbreviated as XO) was filled by the highest ranking officer assigned to the ship aside from the captain. The position was not a separate assignment as it later became. The designated first officer performed their normal duties until it became necessary for them to take command.
This had changed by the late 24th century, when the XO's position had become a completely separate position in a starship's crew held by an officer of commander or lieutenant commander rank grade who held no other position aboard the vessel.
Noted functions of the first officer aboard a Federation starship were:
- Carrying out the decisions of the captain (TNG: "Gambit, Part II")
- Acting as the officer in charge of personnel (VOY: "Day of Honor")
- Managing the ship's resources, including systems allocation (TNG: "Lessons")
After the executive officer, command responsibilities passed down the chain from officer to officer as necessary in accordance with each officer's rank. It was common practice for a commanding officer to designate a second officer to take command if both the captain and first officer were unavailable or unable to perform their duties.
Lt. Commander Data served as operations officer and second officer on board the USS Enterprise-D from 2364 until the vessel's destruction in 2371. (Star Trek Generations)
Discipline and respect of chain of command
When Captain Jonathan Archer reverse-imprinted on a group of Xindi-Insectoids, his increasingly unusual actions led some of his fellow officers to openly question or defy his orders. He relieved those officers and stated to Major J. Hayes that he needed officers who could respect the chain of command and follow orders. (ENT: "Hatchery")
Mutiny was an inherent violation of the chain of command, something that was not lost on Captain Philippa Georgiou when she ordered Commander Michael Burnham arrested for incapacitating her and attempting to order a preemptive strike on the Sarcophagus. (DIS: "Battle at the Binary Stars")
When Spock inquired to Dr. McCoy if he had noticed Captain Kirk acting strangely lately, McCoy replied, "the man on top walks a lonely street. The chain of command is often a noose." In response to McCoy's words, Spock told him to "spare me your philosophical metaphors." Spock then pointed out Kirk's transfer of Kevin Riley to engineering, and McCoy explained that "he's the captain, he can transfer whoever he pleases," adding "you can look that up in a hundred volumes of space regulations somewhere." (TOS: "The Conscience of the King")
Maintaining discipline within this structure was important. In 2286, the Human President of the United Federation of Planets felt sure that Admiral Kirk, who faced a sole remaining charge of "disobeying orders of a superior officer", knew how necessary maintaining discipline was. Kirk concurred, leading the president to demote him to his preferred rank of captain. (Star Trek IV: The Voyage Home)
According to General Chang, Kirk's record displayed his willingness to violate the chain of command whenever he wished. (Star Trek VI: The Undiscovered Country)
During Ensign Mendon's 2365 stint aboard the USS Enterprise-D as part of the Officer Exchange Program, he became aware of several procedural items that could make the operation of the starship's bridge more efficient, and requested to share them with Captain Jean-Luc Picard directly. Picard informed him that the chain of command was employed on the Enterprise, and therefore the Benzite should report to Lieutenant Worf. When the ensign apologized, Picard waved his actions off, saying Starfleet should have made that clearer to him when he was assigned to participate in the program. (TNG: "A Matter Of Honor")
Benjamin Sisko learned many things from Captain Leyton aboard the USS Okinawa, including that "a good officer has to respect the chain of command." Leyton believed that without it "Starfleet would cease to function and we wouldn't stand a chance against our enemies." (DS9: "Paradise Lost")
Starfleet Command thought Constable Odo's respect for the chain of command was "minimal." (DS9: "The Search, Part I")