Star Trek: What Does ISS Stand For?

The "Star Trek" franchise has been around in one form or another since 1966, and that means that the canon is incredibly expansive. It's impossible to know everything there is to know about "Star Trek," and many fans have one specialty or another. Some fans are really big on story and can name the big moments of every episode, while others are character obsessives who can basically give detailed biographies of their favorite "Star Trek" characters on the fly. And then there are the ship fans, who know everything there is to know about the various space-faring vessels in the franchise — and they have a whole heck of a lot to know. 

There is a tremendous amount of thought and detail put into the ships on "Star Trek," all founded on four explicit design rules set forth by creator Gene Roddenberry, and that attention to detail also carries over into things like the ship's names. There are rules for how each class of Starfleet ships are named, which can lead to headaches for series showrunners like Mike McMahan of "Star Trek: Lower Decks," and Federation ships also tend to have a designation at the beginning of them: "USS."

Though "USS" probably came from the "United States Ship" designation of ships in the U.S. Navy, in the fictional Federation of the "Trek" universe, it stands for something else entirely. But there are some ships in "Star Trek" with the designation "ISS," and since it probably doesn't mean "International Space Station" as it does in the real world, what does it mean?

"Star Trek" has entertained the idea of multiverses going all the way back to "Star Trek: The Original Series," when Captain James T. Kirk ended up visiting the Mirror Universe. He visited the strange place, which serves as a direct counter to the Prime Universe, for the first time in the episode "Mirror, Mirror." The Mirror Universe flips major elements on their head, creating "evil" versions of good characters and so on, allowing for the actors to really go wild and have a blast playing their opposites. In the Mirror Universe, the Federation never came to exist and its corollary, the Terran Empire, was overthrown by the Klingon-Cardassian Alliance. Terrans were enslaved and many of their ships seized, but those Empire-built ships still maintain their old names, which start with ISS: "Imperial Star Ship." 

The Mirror Universe has appeared in "The Original Series," "Star Trek: Deep Space Nine," "Star Trek: Enterprise," "Star Trek: Discovery," and "Star Trek: Lower Decks," though no series visited as often as "Deep Space Nine." In the weird, dark offshoot of the franchise, characters from the Prime Universe helped the Terran rebellion in the Mirror Universe, eventually even helping them create a "new" Terran ship: the ISS Defiant, based on the schematics of the USS Defiant. Since the original Defiant is one of the coolest and most important ships in all of "Star Trek," having it significantly helps the Terrans fight back against their oppressors in the Alliance. Whether it starts with "USS" or "ISS," the Defiant is always awesome.