How science-fiction navies handle command

Which TV or film science-fiction navies have the most realistic personnel structure, and why?

Stargate leads the comparison, with Battlestar Galactica, Andromeda, Babylon 5, Star Trek, and Star Wars judged by their command structures and political interference.

Stargate leads the comparison because its personnel generally occupy recognizable military roles within a coherent chain of command. The original Battlestar Galactica follows, while Andromeda earns credit for giving people defined responsibilities after its formal military has largely disappeared. Dylan Hunt assigns roles and keeps crew members within them instead of allowing everyone to change jobs at will. Babylon 5 remains plausible in places, but Star Trek becomes difficult to explain above captain and below lieutenant when the comparison is confined to television and film. Star Wars has a workable hierarchy whose operation is complicated by political influence. A later disagreement over Galactica turns out to concern different versions: Dragon criticizes the reboot, while Alex clarifies that he was judging the original series. The discussion also separates recognizable admiral ranks in Star Trek from the credibility of the admirals' conduct.