Ok, time to throw on the brakes on this crazy train:
Guys, they have a canon number they hold (1 company or approximately 80-200 men). Further, these drop ships are big BECAUSE THEY ARE THE BARRACKS! There is NO internal barracks in this ship. They carry a rack of 27 of these externally. This is NOT the same as a Lathe pattern hanger as there is no force field keeping anything in, they are CONTINUOUSLY exposed to the void. The troops DO NOT EXIT THEM AT ANY TIME and have NO ACCESS TO THE SHIP. They have to carry air and water plants sufficient to provide for the IG troops on board for the duration of the journey from wherever IG is embarking from, to wherever they are being dropped at. The description of it makes a point of bringing this up.
In addition, the SM Strike cruiser does not carry a lathe pattern either, as they can conduct through decks operations (ie they fly the thunderhawk through one side of the hanger and out the other, stopping to refuel and rearm), which would be impossible in a lathe. They're actually similar to a Jovian in that the thunderhawk can fly entirely through the ship.
Strike cruises have as few as one and as many as 3 prow slots, and are able to fit launch bays, bombardment cannon, and torpedoes at the same time (Though this last may be unique to the Ultramarines).