51cm Twin Gun Mount
|Coastal Defense Ship||Destroyer|
|Light Cruiser||Torpedo Cruiser|
|Heavy Cruiser||Training Cruiser|
|Aviation Cruiser||Fast Battleship|
|Light Carrier||Standard Aircraft Carrier|
|Armored Carrier||Seaplane Tender|
|Submarine||Aircraft Carrying Submarine|
|Submarine Tender||Fleet Oiler|
|Repair Ship||Amphibious Assault Ship|
- Winter 2018 Event E-7 Medium/Hard reward.
|Improvement Cost: 100 700 950 200||★||S||M||T||W||T||F||S||Helper Ship|
|Consumes: 4x 41cm Twin Gun Mount||0||20/25||7/8||M||✗||✗||✗||✗||M||M||Musashi Kai Ni|
|Consumes: 4x 46cm Triple Gun Mount||6||25/50||10/13|
Officially known as the 51 cm/45 Type 98 naval gun, it was supposed to be used by the A-150 battleship design (or Yamato Kai) that were never built. 2 complete guns were finished just before the start of the Pacific War but since the A-150 battleships were never ordered, they were left in storage until the end of the war, where they were probably destroyed. Mechanically, they were the same as the 46 cm and constructed with the same techniques as the 46 cm.