Redshirt Deaths in TOS
In The Original Series under Captain Kirk's command, Enterprise crew members of "minor importance" were frequently killed by hostile aliens or in freak accidents, in landing parties as well as aboard the ship. Purportedly most of them wore the red uniform shirt of the engineering/security department, which earned the stock character of an expendable crewman the name "Redshirt" in popular culture. The following is a complete list of all casualties during the original Enterprise's five-year mission, with some interesting statistics.
List of Casualties
We could witness the deaths of the following crew members on screen, or they were reported to have died. The casualties are listed in chronological order (by production numbers).
Addendum
"Resurrection"
The following crew member was dead by 23rd century medical standards but was brought back to life.
- Montgomery Scott was killed and later revived by Nomad in "The Changeling".
Illusory deaths
The deaths of the following crew members turned out to be just illusions. Unsurprisingly no member of the principal recurring cast of TOS ever remained dead.
- Angela Martine-Teller and Leonard McCoy appeared to have been killed in "Shore Leave".
- Pavel Chekov's death turned out an illusion in "Spectre of the Gun".
TAS
No one of the Enterprise crew died in The Animated Series.
Summary
56 crew members can be confirmed to have died on the original Enterprise's five-year mission (or, to be precise, during the about three years shown in TOS). This gives us 0.7 casualties per episode, or roughly one casualty every three weeks. 26 of those 55 killed men or women were wearing a red shirt or an equivalent red engineering/security uniform. Considering that the shirt color of 15 deceased crew members remains unknown (because they were killed off screen or were not wearing a standard uniform), redshirts easily make up more than 50% of all casualties. The myth that more redshirts than other colors are killed can be confirmed. Some of the redshirts were engineers but most performed the duty of a security officer, which may be rated as intrinsically more dangerous and more likely lethal.
Looking at the subtotals we can notice that in season 1 only 4 crew members with red shirts were killed, 4 wearing blue shirts and as many as 7 with gold/yellow shirts. Considering that a couple of the two latter groups effectively acted as security officers, especially in "The Man Trap", it is possible that the red color for this department was not yet set in stone at the time. Season 2 had by far the most redshirt deaths of the series, 16 altogether. 12 of those 16 were killed in just three episodes, "The Changeling", "The Apple" and "Obsession".
Only 4 women were killed under Kirk's command, as opposed to 39 men. This is significantly less than the ratio of female to male Enterprise crew members. Considering that in the 1960s women were obviously not deemed fit for a position in the security department with its high casualty rate, the low number of female deaths appears plausible though.
The clearly most common cause of death among Kirk's crew was an attack or sabotage by aliens (38 casualties). 12 crew members died in accidents, but if we take into account that as many as 9 perished when the ship crossed the Galactic Barrier in "Where No Man Has Gone Before", accidents were otherwise not that common at all. 6 of the crew died of diseases. Regarding the places in which crew members were killed, the Enterprise proved to be just as unsafe (29 casualties) as the surface of an unexplored planet (27).
Further Commentary
The fact that the majority of the crew members that died during TOS wore a red shirt is indisputable. This doesn't mean that they are also most likely to be killed, however. There is a lot of disagreement about this question because there are various figures that the crew deaths may be referred to in order to calculate a probability.
Several articles come to the conclusion that other colors (usually gold shirts) are more likely to be killed, based on the assumption that more than 50% of Kirk's 400 or 430 crew members are redshirts. This is hard to verify because we usually see crew members besides the main characters in specific roles with specific shirt colors, which may not be representative of the crew as a whole. Yellow is quite common on the bridge, red is prevalent in engineering, sickbay is all-blue. We may want to leave such places aside, and also situations that specifically require the presence of science, medical, security or engineering personnel. If we focus on random encounters in corridors or recreation rooms, my impression is that a slight majority are gold shirts, followed by blue and red. A definite figure of 239 engineering, security and operations personnel in red on the Enterprise is sometimes cited as proof for their prevalence in articles, yet this comes from the non-canon Star Fleet Technical Manual.
There are also attempts to calculate a probability of landing party members to be killed on an alien planet. As I already summed up above, the Enterprise seems to be just as dangerous a place for the crew. Still, we may focus on those that beam down, and we may choose to exclude the main characters, who naturally always survive. In this case, the percentage of the many redshirts that die may be lower than that of the overall fewer blue and yellow shirts in landing parties.
See Also
Biography Inconsistencies - gaps in biographies and other anomalies
Credits
Some facts are from Memory Alpha, the HD screen caps are taken from TrekCore. Thanks to Frank Bitterhof for the hint about the technicians in "The Changeling" and the suggestion to declare Leslie's death in "Obsession".