According to a DVD interview, Vaughn Armstrong was called shortly before shooting and told he was needed to fill the role of the Klingon Commander. The most challenging aspect of this sudden call, in his opinion, was having to deliver the Klingon language so precisely so as to not upset established Klingon language guidelines.
Vaughn Armstrong, who plays the recurring character of Admiral Forrest in this series, also plays the captain of the crippled Klingon ship. Interestingly enough, Armstrong's first Star Trek role was as Korris, one of the Klingons in Heart of Glory (1988), the first TNG depiction of Klingons.
First chronological mention of: the photon torpedoes gagh, the Klingon delicacy Klingon Raptor-class scout vessel. Tucker describes the Klingon vessel as a "tough little ship." This is a phrase used by William T. Riker and Thomas Riker, both referring to the USS Defiant, in Star Trek: First Contact (1996) and Defiant (1994) respectively. This is also the first appearance of an entirely computer-generated targ, and the first time in the series someone catches a cold. Thus, so far, a cure for the cold has not yet been found. It was mentioned in an episode of TNG that a cure has finally been found.
The "siren sounds" made by the E.M. waves coming from the gas giant are the same sounds made by the alien probe in Star Trek IV: The Voyage Home (1986).
Archer says that this is the third time Enterprise has run into the Klingons. This confirms that the only other canon appearances by the Klingons up until this episode were seen in Broken Bow, Part 1 (2001) and Unexpected (2001); there were no encounters "off-screen."