 When design work began , the navy department was asked to submit new requirements to fix deficiencies found in the preceding battlecruiser classes , which primarily covered propulsion systems and the main armament . Previous battlecruisers used a four shaft arrangement for their engines ; reducing the number to three would allow the new ships to equip a diesel engine on the central shaft . This would substantially increase the cruising range , and would ease the transfer of fuel and reduce the number of crew needed to operate the ships ' machinery . The navy department also argued for an increase in the main battery guns , from 28 @-@ centimeter ( 11 in ) guns to 30 @.@ 5 cm ( 12 in ) weapons . This was because the latest British battleships had thicker main belt armor , up to 300 millimeters ( 12 in ) . Since the German battlecruisers were intended to fight in the line of battle , their armament needed to be sufficiently powerful to penetrate the armor of their British opponents . <unk> increases were managed by reducing the number of guns , from 10 to 8 — the increase in gun caliber added only 36 tons to the ships ' displacement . Tirpitz argued against the increase in gun caliber , for he thought the 28 cm gun was powerful enough . 
