A USO, or Unidentified Submersible Object is like a UFO (Unidentified Flying Object) but is able to maneuver through water.
Mainbrace is defined as the rope used as support for the masts, running from the bow to the top of the mast and back to the deck.
Shipboard scenes were filmed aboard the former US Navy Destroyer, USS Turner Joy (DD 951). She is a museum ship located in Bremerton, Washington, not far from where the show is filmed in British Columbia, Canada.
Faux Paux: USAF (United States Air Force) Captain Quinn should know Naval Protocol being a military officer and when he is introduced to the Admiral on the bridge, he should have asked "Permission to come aboard Sir?" Not thanking him until after he and Dr. Hynek are granted permission to come aboard.
At the end of the episode it seems to be that there is a character that highly resembles Indiana Jones.