Specialist wouldn't be in regular ranking, a specialist is... Well, a specialist, they're medics/engineers/sharpshooters, etc. They sorta act like specialized divisions sergeants. Also, in the federation, there are no 1st sergeants. It'd be replaced with a master sergeant or tech sarge. Same with Lieutenants. No 1st or 2nd, just lieutenant. Also for fleet, it wouldn't be cadet then spaceman, petty officers follow suit. 3PO, 2PO, 1PO, CPO, SCPO. Still, just a suggestion.