Writing and story "Zero Hour" was the culmination of a season-long
story arc first introduced by the events of "
The Expanse", wherein an alien race called the Xindi attacks Earth and kills seven million people. During the course of the
third season, the
Enterprise went into the previously unexplored Delphic Expanse to search for the Xindi and to prevent a further attack which will destroy Earth. Executive producer and writer
Brannon Braga felt that the end of the season in a three-part arc composed of "
The Council", "
Countdown" and "Zero Hour", which he compared to three acts of the same story. The idea that
Enterprise would be successful in its mission was planned from the start of the development of the year-long story. However, the producers and writing team would joke that there would be a "bizarre twist" such as the crew returning to Earth and discovering that it was now ruled by giant
cockroaches. The writers decided against a Xindi-based cliffhanger and sought an unusual twist. Braga said that "I can't remember who said '
Nazis,' but we just somehow ended up with Nazis. Then that didn't even feel like enough, so we decided to make them alien Nazis." Actor
Dominic Keating, who portrays
Malcolm Reed on
Enterprise, called the ending a "lovely twist... that just makes you scratch your head and wonder at what you've just seen." It was the third time that Nazis had appeared in the
Star Trek franchise. The first was in the episode "
Patterns of Force" in
Star Trek: The Original Series, and then again on the
holodeck on
Star Trek: Voyager in the two-part "
The Killing Game". In the episode, T'Pol states that "Zero Hour" takes place in 2152, a statement which contradicts other episodes.
Manny Coto, executive producer and show runner for the following season, explained that this was a mistake in the script. It was later stated in the timeline published in
Voyages of Imagination by Jeff Ayers that the events of "Zero Hour" took place on February 14, 2154, a day after the setting of the episode "Countdown".
Direction, filming and guest stars Allan Kroeker directed the episode. He had previously directed the
season two closing episode "The Expanse", and the first episode of season three, "
The Xindi". Previously in the franchise, he had directed the finale of both
Star Trek: Deep Space Nine and
Star Trek: Voyager. Production began on March 5 and was completed eight working days later. "Zero Hour" was the final episode of
Enterprise to be shot on
film stock, as for the following season, the decision was made to switch to high-definition
digital video. Scott Bakula stated in an interview on
The Wayne Brady Show that there were three endings to the episode filmed. This was later denied by Dominic Keating while on stage at
Creation Entertainment's Grand Slam event in Pasadena in March 2004. He did clarify that the script for the final scene was delivered to his house in three envelopes, accompanied by a security guard with a dog. "Zero Hour" featured a guest and stunt cast larger than usual for episodes of
Enterprise. Boehmer noted that the episode was filmed with a higher than normal level of secrecy, as it was the first time he did not receive a complete script and was only given his specific pages, which included warnings not to disclose anything about the episode. In addition to the actors appearing on the episode, two members of the public made walk on appearances as Starfleet crewmen on the engineering set. These were Amy Ulen, who had won the prize on
KZOK-FM. Joining her was
DJ Bob Rivers from the Seattle-based
UPN affiliate radio station. Also appearing was Brian D'Arcy who gained his role through a charity auction held by
Wired magazine to benefit the
Starbright Foundation. ==Reception==