There's no rule that says that in the blue book. The only restriction is that you can take one battle barge per 1000pts or part thereof.Yeah, I may have been out of BFG for a little while, but I'm pretty sure the rules still require you to take a couple of cruisers before you can use a battleship; unless of course marine fleets have a rule to counter that in their pdf/entry in the armada rulebook.
Those are restrictions on the Imperial Fleets. The rules are attached to that list and that list only. This fleet can use either the Armageddeon or Astartes lists and still be legal.I'm not one hundred percent sure about the armada rulebook; but I do know that the BFG rulebook I have does require imperial fleets to take at least three cruisers for every one battleship. Now I know that armada is additional/revised rules but I don't ever recall that requirement being lifted in imperial fleets. (Though I do remember there being some sort of point value a fleet was supposed to be for a battlebarge to be taken.)
Obviously this isn't a serious this (see the thread title). It's just have I have a spare battle barge lying around and thought it would be fun to throw it into a battle.As for the 'list' itself, I think its kind of weak; one large/slow ship can be beaten pretty easily by almost all of the other fleets out there since most of them can have better range and more maneuverability. (Chaos, eldar, dark eldar, orks, and tyranids would probably have very little trouble taking on a lone battlebarge.)