There are frequent mentions in the second half of the first season of Star Trek: Discovery of the U.S.S. Defiant

which apparently was the first ship to cross from the Prime Universe to the Mirror Universe in this timeline.

Am I supposed to know about this already? What is the supposed backstory and in which episodes were these events depicted or described?

  • 3
    Am I supposed to know about this already? Yes, yes you are. See my answer to your question here: scifi.stackexchange.com/questions/105508/…
    – Praxis
    Jan 23, 2018 at 18:42
  • @Praxis: What are you complaining about? I provide the questions. You provide the answers. Jan 24, 2018 at 4:06
  • 1
    I'm not complaining. I'm just saying that, in theory, you would have encountered this very info before. :-)
    – Praxis
    Jan 24, 2018 at 4:09
  • @Praxis: Yeah, I guess that didn't register with me at the time. Jan 24, 2018 at 17:24

1 Answer 1


The USS Defiant (NCC-1764) has made two prior appearances on two different Star Trek shows.

It first appeared in the original series, in the season 3 episode "The Tholian Web". The central conflict of that episode is that the Defiant is being pulled into a bizarre spatial anomaly, and it disappears completely by the end:

Scotty: Then your fears about that phaser were correct. It blasted a hole right through that crazy space fabric, and only heaven knows where it sent the Defiant.

Star Trek: The Original Series Season 3 Episode 9: "The Tholian Web"

The ultimate fate of the Defiant was left ambiguous until one of the Enterprise writers decided to write a sequel to it, set in the Mirror Universe. This turned into the Enterprise two-parter "In a Mirror, Darkly", which established that the Defiant was transported into the Mirror Universe's past (so it travelled between universes, and also through time) and became something of a secret weapon for the Terran Empire:

Mirror!Archer: The Tholians are a little more open-minded than [the Vulcans]. They detonated a tricobalt warhead here, inside the gravity well of a dead star. The explosion created an interphasic rift. A doorway into another universe.

Mirror!Trip: A doorway.

Mirror!Archer: The rift was unstable. It was too dangerous to send one of their own ships through, so they transmitted a distress call into the opening, hoping to lure a ship from the other side. Their plan worked brilliantly.


[Just sticking out of the moon is the saucer section of NCC1764.]

Star Trek Enterprise Season 4 Episode 18: "In a Mirror, Darkly, Part 1"

However, none of this is required reading for Discovery; the relevant information for those purposes, that the Defiant is a ship from the prime universe that crossed over into the Mirror universe, is established in "Despite Yourself", the first episode of Discovery fully set in the Mirror universe:

Lorca: Data from rebel intelligence suggests that we're not the first ship from our universe to find ourselves here. It cites another Starfleet vessel: USS Defiant.


Burnham: It's unclear, but data suggests that in the future, Defiant will encounter a phenomenon that'll bring it into this alternative universe's past.

Star Trek: Discovery Season 1 Episode 10: "Despite Yourself"

Since Discovery is set prior to the events of "The Tholian Web", this means that from their perspective the Defiant hasn't disappeared yet; however, because the Defiant travels through time, it's still present in the Mirror Universe at the time Discovery gets there.

I hate temporal mechanics.

  • Can you clarify your first few sentences? It not clear to me which episode you mean by "which episode"? Also, it's not clear is "TOS era" is supposed to include Discovery? Jan 23, 2018 at 18:23
  • 1
    @ThePopMachine I was in the middle of an edit, but I'm not sure how I can clarify it any further. The Enterprise episode is "In a Mirror, Darkly", and that episode refers back to "The Tholian Web", from TOS (that's where the Defiant was first introduced). It's not strictly relevant to the question, but Saru mentions in "Despite Yourself" (Discovery episode) that the Defiant is contemporary to their timeline; it doesn't disappear until the TOS episode, which occurs several years later Jan 23, 2018 at 18:26
  • You say "refers back", but ENT is before TOS chronologically. So I don't get what's supposed to be going on... Jan 23, 2018 at 18:42
  • 1
    @ThePopMachine The ship travelled through time as well as through universes. So despite being set earlier in time, the Enterprise episode is a sequel to the TOS episode. I edited again to make the timeline a little more apparent Jan 23, 2018 at 18:48
  • 3
    @ThePopMachine Visual aid. And yes, I do accept commissions. Support my Patreon! Jan 23, 2018 at 19:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.