I'm sure there are all sorts of things that others latch on to as problems in the series, but re-reading it, the things I notice are all minor stuff regarding Navy protocols and such, particularly submarine ones. For example, in Ch 7 of Vorpal Blade, the XO of the Blade, an experienced sub CO, uses "closed" when talking about stowing the screw (propeller) for the space drive part of the official first trip, but submariners never use "close" or its variants, but "shut". "Close" is too close to "blow" (as in ballast tanks), which in a combat situation could result in Bad Things(tm) due to misunderstanding communications. I realize Ringo was Army, but surely he had some Navy guysnote not including me; aside from getting a cameo in LFoD for my buying an "OH JOHN RINGO NO" SHIRT he doesn't know me, nor is that likely to change any time soon to ask about those kinds of details...
Me, I'm bugged that there ain't no Coasties in space. Or, failing that, the Coast Guard doesn't eat the Navy. As I remember there was talk of a "Sea Guard" instead of the very simple obvious solution of commissioning the USCGC Nimitz and all her friends.
Where does the waste heat from the wyvern's nuclear reactors go when they're in space?