Design A - 150 battleship Design A - 150 , also known as the " Super Yamato " class , was an Imperial Japanese plan for a class of battleship s . Begun in 1938 – 39 , the design was mostly complete by 1941 . However , so that a demand for other types of warships could be met , all work on Design A - 150 was halted and no keels were laid . Authors William H . Garzke and Robert O . Dulin have argued that Design A - 150 would have been the " most powerful battleships in history " because of the massive size of their main battery of six guns as well as numerous smaller caliber weapons . Design . Background . Initial plans for the A - 150 battleships called for eight or nine guns in quadruple or triple turrets . The successful construction of a gun in 1920 – 1921 made the Japanese confident that a could be built . In addition , a top speed of 30 kn ( 35 mph ; 56 km / h ) was desired so that the class would be faster than the United States ' " North Carolina " - class battleship s . However , these grand specifications were curtailed when tests culminated in a ship that had a displacement of some 90 , 000 tons ; it was felt that ships of this size would be " too large and too expensive " . Specifications . Initial design studies were undertaken after the completion of plans for the " Yamato " class ( 1938 – 39 ) ; they focused on a ship with a displacement nearer to that of the " Yamato " s . As the Japanese expected that the Americans would be able to obtain the true characteristics of that class ( namely the principal armament of ) , the use of 510 mm guns was vital to keep with Japan ' s policy of individual ships ' superiority over their American counterparts ; the A - 150s were meant to counter the United States ' reply to the " Yamato " s . Plans were " essentially completed " sometime in 1941 ; however , similar to the fate of documents relating to the " Yamato " class , most papers and all plans relating to the class were destroyed at the end of the war , meaning that the full specifications of the ships are not known . It is known the ships would have had greater firepower than the " Yamato " class : a main battery of six 510 mm ( 20 . 1 inch ) guns in three twin turrets and a secondary armament of " many " / 65 caliber guns . The displacement was to be similar to the " Yamato " class , which was around 60 , 000 – 70 , 000 tonnes . The side armor belt was probably going to be . This was so large that steel mills in Japan were incapable of manufacturing it ; instead , " double strake s of armor plates " were going to be utilized , which would have been much less effective than just one single plate . Armament . Although details of the smaller armament planned for the ships are not given in sources , a main battery of six / 45 caliber guns in dual turrets was definitely planned . These would have been the largest ever fitted to a capital ship , dwarfing the guns mounted on the " Yamato " class . By 1941 , one — possibly two — of the 510 mm guns were being constructed at the Kure Naval Arsenal and detailed designs of the turrets that would hold the guns were drawn up . The turrets would have weighed and trained at per second through a range of to port or starboard . The guns themselves could have fired at a maximum rate of 1 to 1 . 5 rounds per minute and be elevated from to , with the elevation rate being per second . They would have weighed and would have been long . The bore length was to have been around . The armor - piercing ammunition would have weighed between 1900 and 2000 kg ( 4190 – 4409 lbs ) , while the high explosive rounds would have been . A secondary battery of " many " / 65 caliber guns was being considered , although this was not final . This design was the best anti - aircraft gun produced by Japan during the Second World War . Overall , the weapons compared very well with other contemporary weapons . The key advantages that made it so successful — the " high muzzle velocity and a fast rate of fire " — resulted in a short 350 – 400 - round service life . In anti - aircraft defense , their ceiling at was , although the effective range was . They were able to fire 15 – 21 rounds per minute . In " Battleships : Axis and Neutral Battleships in World War II " , authors William H . Garzke and Robert O . Dulin argued that Design A - 150 would have been the " most powerful battleships in history " because of the titanic main armament and the use of a dual purpose secondary battery . Construction . With war on the horizon in early 1941 , all design work was diverted from battleships — even though the A - 150s ' design was virtually complete — so that a demand for " aircraft carrier s , cruiser s , and smaller ships " could be met . Even though no work was being done on them , two ships of Design A - 150 , provisionally designated as Warships Number 798 and 799 , were projected in a 1942 building program . 798 was to be built in the same dock as , while 799 was to be built in Kure in the same dock as after the fourth ship in the class , Warship Number 111 , was launched . Both of the ships ' keels were supposed to be laid in late 1941 or early 1942 , launched in 1944 / 45 , and finished in 1946 / 47 . However , the war ' s turn against the Japanese after the Battle of Midway meant that the need for ships other than battleships never abated .