Three of Elizabeth Moon's Serrano Legacy series - the final three, as I picked up the first three in an omnibus over a year ago and then the fourth one at a library somewhere. These were also all library, as, alas, they don't pass my "do I want to spend money on this?" test. Rules of Engagement, Change of Command, Against the Odds.

(  They're military sf or space opera, depending on how fussy you are about definitions. )