 On 12 June 1917 , well before Mutsu was laid down , Hiraga proposed a revised design for the ship that reflected the lessons from the Battle of Jutland that had occurred the previous year , and incorporated advances in boiler technology . Given project number A @-@ 125 , his design added an extra twin main @-@ gun turret , using space and weight made available by the reduction of the number of boilers from 21 to 12 , while the power remained the same . He reduced the secondary armament from 20 guns to 16 , although they were raised in height to improve their ability to fire during heavy weather and to improve their arcs of fire . To increase the ship 's protection he proposed angling the belt armor outwards to improve its resistance to horizontal fire , and increasing the thickness of the lower deck armor and the torpedo bulkhead . Hiraga also planned to add anti @-@ torpedo bulges to improve underwater protection . He estimated that his ship would displace as much as Nagato , although it would cost about a million yen more . Hiraga 's changes would have considerably delayed Mutsu 's completion and were rejected by the Navy Ministry . 
