The USS Defiant is the name of Ben Sisko's ship in Star Trek: Deep Space Nine whose crew wore The Original Series uniforms for "Trials And Tribble-ations ".

Also another note, Captain Archer wears the uniform worn by Jim Kirk in the Star Trek: The Original Series episode "The Trouble With Tribbles". (Exact same greenish color too.)

The final battle between Phlox and Tucker was scripted originally to be filmed in the Emergency Manual Monitor, a room overlooking Main Engineering. However, the expense of building this set, and the CG effects showing Engineering through the window, demanded the scene be scrapped and it was then moved to the access tunnels.

This is the only episode of Star Trek: Enterprise not to feature a starship named Enterprise, since Captain Forrest's ship was destroyed in "In a Mirror, Darkly, Part I".