Military ranks

I love Babylon 5 but I must say the madhouse up of military ranks is annoying! Our military are very fond of they structure and has not changed since before the American revolution, I doubt it would change by 2258.

We see ranks on B5 of Captain, commander, lieutenant commander, lieutenant, lieutenant junior grade, and chief warrant officer. All ranks in the Navy. So why the heck are GENERALS, not admirals, controlling a fleet of earth ships? Why was Ivanova made a general? The marine arc (with Dodger and General Franklin) got it right, they are marines. But the general -v- adniral thing is So irritating!