15.5cm Triple Secondary Gun Mount
|Coastal Defense Ship||Destroyer|
|Light Cruiser||Torpedo Cruiser|
|Heavy Cruiser||Training Cruiser|
|Aviation Cruiser||Fast Battleship|
|Light Carrier||Standard Carrier|
|Armored Carrier||Seaplane Tender|
|Submarine||Aircraft Carrying Submarine|
|Submarine Tender||Fleet Oiler|
|Repair Ship||Amphibious Assault Ship|
Although designed to be a part of the cruiser's main battery, it saw a more practical use as the battleship's secondary armament. The Yamato-class was designed with this, for potential use as an anti-aircraft gun, however its combined ability and performance were outstanding enough to be used as the battleship's secondary armament. However, the turret section's armor was very thin, resulting in various rumors about it being the Yamato-class' Achilles' heel when pointed out.
According to here, the Mogami-class and eventually the Tone-class was supposed to carry the gun. But when more practical use was seen on Yamato-class and Ooyodo, it then remained as part of the battleship's main weaponry. One factor for the gun design change was that the gun was supposed to have an additional 75 degrees for AA firing on top of the main 45 degrees for general firing, but this was switched to +55 degrees for the reasoning that it was too inefficient.
The "Achilles' heel" portion refers to the relatively inferior armor thickness of the turret part, albeit being colossally improved compared to casemate guns of other Japanese battleships (Fusou-class to Nagato-class).