The converted carrier aircraft were heavier versions of their land-based predecessors and this required a host of changes to "Graf Zeppelin"s original design: the existing catapults needed modernization; stronger winches were necessary for the arresting gear; the flight deck, elevators and hangar floors also required reinforcement. Changes in naval technology dictated other alterations as well: installation of air search radar sets and antennas; upgraded radio equipment; an armored fighter-director cabin mounted on the main mast (which in turn meant a heavier, sturdier mast to accommodate the cabin's added weight); extra armoring for the bridge and fire control center; a new curved funnel cap to shield the fighter-director cabin from smoke; replacing the single-mount 20mm AA guns with quadruple "Flakvierling" 38 guns (with a corresponding increase in ammunition supply) to improve overall AA defense; and additional bulges on either side of the hull to preserve the ship's stability under all this added weight.