Theory(ies) about the giants.
Since it was revealed that the Vice Admirals can use haki, I wondered if the VA giants (Lacroix and Ronse) also can.
In my opinion they can't. And not because they proved to be almost useless in the war, but because they're giants. We can all agree giants are stronger and more resistant than simple humans therefore it's easier for them to "climb the ladder" (meaning get promotions). Also, they live longer. Now it probably seems a little unfair but just think about it. Not many giants want to obey a man so little they can barely see him. There are exceptions like the Giant Squad and John Giant. Still, it's unlikely that a small human ever gave orders to the marine giants (the war is an exception of course). I think there always were a higher ranked giant to command the squad (now there are two Vice-Admirals, it's more than enough). If John Giant is part of the squad somehow(I doubt it), he's the leader, if not, Lacroix is.
I don't have any idea how the marines were able to collect eight giants (John Giant seems to be somewhat special so I'm not counting him), I hope the manga will reveal that or anything else about the Giant Squad.
Feel free to prove that these are wrong, I might be mistaken.