O - class battlecruiser The O class was a planned class of three battlecruiser s for the " Kriegsmarine " ( German Navy ) before the Second World War . Prompted by a perceived lack in ship numbers when compared with the British Royal Navy , the O class ' design was born with the suggestion of modifying the design with guns instead of . The ships were incorporated into the 1939 Plan Z ; while an aircraft carrier , H - class battleships and smaller ships engaged convoy escorts , one or more O - class ships would attack the merchant ships . The O class ' design reflected their intended role ; a heavy main armament — six 380 mm guns in three dual turrets — for possible encounters with escorting - armed heavy cruiser s , enough armor to defend against the same and nothing more , and a high top speed so that they could get away from slower but much better armored capital ship s . Genesis : P - class cruisers . Even with the completion of the two s and the construction of two s , the German Navy had fewer ships than other European navies . This led to a decision in 1937 to build ships to an improved design . After more than twenty designs were considered to meet the navy ' s specifications , one was chosen ; it was designated as cruiser " P " ( the " P " for panzer — German : " armor " ) . Under the original plan , twelve P - class ships were to be built . The ships were designed as cruiser killer s that would have heavy enough armament and armor to take on light and heavy cruiser s but enough speed to outrun battleship s and battlecruisers . Many problems were encountered with designing the ships , the most prevalent being armor . The required maximum speed of 34 knots meant that the minimum length had to grow from the original to . It also meant that the beam could be a minimum of — unless diesel engines , like those used in the " Deutschland " s , were desired ; they would increase the beam by . Unfortunately for the designers , the widened beam meant that an even longer hull was needed to maintain hydrodynamic efficiency . All of this complicated the armor arrangements , as more armor was needed to cover the longer length and widened beam . Eventually it was deemed that it was impossible to include diesel power on a displacement . The switch to battlecruisers was the result of a proposal to up the main armament from / 55 caliber guns to / 47 caliber guns . Various reasons were behind this . Among other reasons , experiments showed that the smaller gun was " far less effective " than the larger gun , a class of twelve ships would have overtaxed the shipyards already heavily burdened with other ships , and the smallest guns on any foreign ship in service or under construction were more than larger than the 283 mm guns . The most persuasive argument for increasing the armament came in 1939 , when Adolf Hitler denounced the 1935 Anglo - German Naval Agreement . Battlecruisers . Although interest in the P - class ships and the battlecruiser proposal waned for a time in late 1937 and early 1938 , it was quickly revived on 28 April 1938 with Hitler ' s public airing of his views on the 1935 Anglo - German Treaty and the consequent increased possibility of war with the United Kingdom . Calling the Naval Staff and Admiral Erich Raeder to him , Hitler laid out his thoughts of a strong navy that could pose enough danger to the British such that they would enter into an alliance with Germany rather than go to war . As decided here , Plan Z entailed two task force s each centered around three H - class battleships and one aircraft carrier , with cruiser s and destroyer s as escorts . In war , these forces would collaborate with the three battlecruisers by occupying convoy screens while U - boat s and one or more of the O class took out the cargo - carrying merchant ships . The presence of the battlecruisers operating at large would have the secondary effect of forcing the Royal Navy to deploy battleships as convoy escorts , thus weakening any fleet that could engage the Plan Z task forces . As part of the plan , design work on the P class was halted in mid - 1939 in favor of the O class . Displacement was limited to in the new designs so that the length of construction would be shortened from the normal four or more years that a battleship required , to an estimated three to three and a half years . Required characteristics for the battlecruisers was a displacement of , a main battery of six guns , a secondary battery of dual purpose gun s , a top speed of , a range of at , and enough armor to counter the guns of heavy cruisers . Like the P class , there were problems with fitting an all - diesel drive into the hull of the ships . It was enough that the design team decided that it would not be prudent to use an all - diesel arrangement ; instead , a hybrid diesel - steam turbine propulsion plant was to be used . The change allowed the central armored citadel to be reduced by and the aft beam to be lowered by . Although plans were not finalized , the third battlecruiser , " Q " , was ordered from Germaniawerft in Kiel on 8 August 1939 . One month after , the contract design was refined . The displacement was increased to ( design ) and ( full - load ) , while the draft at those two figures was and , respectively . At the waterline , the length was set at and beam at . The main battery was the same as previously ( six / 47 caliber guns in dual turrets ) , while the secondary battery was split between six paired / 48 caliber anti - surface guns and paired / 65 caliber anti - aircraft guns because German designers had not been able to develop a satisfactory dual - purpose gun . Light anti - aircraft guns were eight 37 mm in four dual mounts and twenty 20 mm autocannon in single mounts . Twelve torpedo tubes finished out the armament aboard the ships . Four floatplanes for scouting were planned . At the design displacement , the maximum speed was reduced by half a knot , to ; this required a top shaft horsepower of 173 , 600 . By 1940 , project drawings for the three battlecruisers were complete . They were reviewed by both Hitler and Admiral Raeder , both of whom approved . However , outside of " initial procurement of materials and the issuance of some procurement orders " , the ships ' keels were never laid . In large part , this was due to severe material shortages , especially of high - grade steel , since there were more pressing needs for these materials for the war effort . In addition , the dockyard personnel necessary for the ships ' construction were by now occupied with more pressing work , primarily on new U - boats . Specifications . General characteristics . The final design , which was completed by 1940 , called for a ship that was long at the waterline and long overall . The planned ships had a beam of and a designed draft of . The ships ' designed displacement was , but displaced standard and at full displacement . The ships were to be of welded steel construction , with 20 watertight compartments and a double bottom that extended for 78 % of the length of the hull . The ships were to have had a crew of 65 officers and 1 , 900 men . They were intended to carry a number of boats aboard , including two picket boat s , two barges , two launches , two pinnaces , two yawls , and two dinghies . The ships were also to be equipped with a double catapult mounted between the two funnels , and four Arado Ar 196 seaplanes for maritime reconnaissance . The aircraft were stored in a main hangar just aft of the forward funnel , along with two smaller hangars , one on each side of the rear funnel . Propulsion . The O - class ships were to be powered by eight MAN 24 - cylinder V - configuration two - stroke diesel engines . The diesels powered two Vulcan gearboxes , both of which drove the outer pair of three - bladed screws that were in diameter . Aft of the diesel engines were four Wagner high - pressure boilers that provided up to 55 atmospheres of pressure . They were mounted in a single boiler room . The boilers supplied steam for one set of Brown , Boveri & Co . turbines , which provided power for the center three - bladed screw . The O - class ships were designed to store 1 , 000 tons fuel oil for the high pressure boilers , and up to 4 , 610 tons of diesel oil for the diesel engines . This enabled a maximum range of 14 , 000 nautical miles at a cruising speed of 19 knots . They were designed to steam at a maximum of 33 . 5 knots , but were capable of up to 35 knots . The ships had two rudders each . Eight 920 kW diesel generators supplied electrical power for the ships , for a total of 7360 kW , at 220 V . Armament . The ships ' main armament batteries were to have consisted of six L / 47 SK C / 34 quick - firing guns mounted in three twin turrets , the same Drh LC / 38 gun turrets as were used on the s . Two of the turrets were mounted in a superfiring pair forward , with the third turret placed aft of the main superstructure . The guns could depress to −8 degrees and elevate to 35 degrees . At maximum elevation , the guns could hit targets away . The guns had a designed supply of 630 shells , for a total of 105 rounds per gun . There were three types of shells : capped armor - penetrating , and two different high - explosive shells ; all three shells weighed . The guns used a fore charge and a main charge in a brass case . This provided a muzzle velocity of 820 meters per second ( 2 , 690 feet per second ) . The secondary battery consisted of six L / 48 SK C / 28 quick - firing guns , also mounted in three twin turrets ; two were placed on either side of the forward superstructure , the third was placed aft of the main superstructure , superfiring over the rear main battery turret . These guns were supplied with 900 rounds , for 150 shells per gun , and had a maximum range of . The ships were also armed with six above - water torpedo tubes , with a total of 18 torpedoes . The ships had an anti - aircraft battery consisting of eight L / 65 SK C / 33 heavy anti - aircraft guns , eight L / 83 SK C / 30 anti - aircraft guns , and twenty . The 10 . 5 cm guns were emplaced in twin mounts , two on either side of the superstructure , as were the 3 . 7 cm guns . The 2 cm SK C / 30 guns were placed in single mounts , dispersed on the superstructure amidships . Armor . The O - class ships were to be protected by Krupp " Wotan " steel armor . The main armored belt was thick in the most critical areas of the ship , including the machinery spaces and ammunition magazines , and in other less important areas ; the armor tapered to zero at the stern and bow of the ship . A torpedo bulkhead ran the length of the hull ; the bulkhead was thick for the majority of its length . A second bulkhead was placed in the central portion of the ship . The bulkhead was thick but increased to in the more important portions of the ship . Critical areas were further protected by 80 mm - thick shields set back from the torpedo bulkhead . All of the lateral armor protection was " Wotan Hart " steel , with the exception of the torpedo bulkhead , which was " Wotan Weich " . The ships had several layers of horizontal deck armor . The upper deck was thick , and the armored deck ranged in thickness from 20 – 80 mm ( . 79 – 3 . 1 in ) ; important areas were also protected by thick overhead shields . The armored belt connected to 110 mm - thick sloping armor . The forward conning tower had a roof 60 mm thick and armored sides ; the aft conning tower was significantly less well protected . The roof was decreased to and the sides were 50 mm thick . The rangefinders were protected against shell splinters by roofs and 30 mm sides . All of this armor was " Wotan Hart " . The main battery turrets had 50 mm thick roofs and sides that were thick . The inner shields were thick . The 15 cm gun turrets had thick protection against shell fragments . All of the anti - aircraft weaponry were also protected with 14 mm - thick gun shields . The aircraft hangars also had 14 mm - thick splinter protection . The relatively thin armor protection given to the ships of the O class led to their derisive nickname " " Ohne Panzer Quatsch " " ( Without armor nonsense ) , a play on their provisional names . Ships of the class . Schlachtkreuzer O Schlachtkreuzer P Schlachtkreuzer Q