In the touching final scene Gibbs and the widow exchange honored and traditional wishes often used among Marines and Navy people; the widow says to Gibbs, "Semper fi", and he responds to her, "Fair winds and following seas".
Chelsea Field guest stars as the Commander's widow. She is the real-life wife of NCIS: New Orleans (2014) star Scott Bakula, which would not premiere until 8 years later.
Early on in Head Case (2006), if you observe the decapitated head closely, particularly in Ducky's lab, it has a striking resemblance to Agent Gibbs (minus the gray hair.) The producers likely did that for fun and used Mark Harmon's face and head as a model base to make the decapitated head for the sake of the episode.
The last command of the dead captain was the fictional USS Manassas (CG-74), a guided-missile cruiser, from which his remains are to be spread at sea; however, no such ship exists, and no ship of the US Navy has ever borne the name of Manassas.
Chelsea Field, who played Jocelyn Wayne, went on to play Rita Devereaux on NCIS: New Orleans (2014).