51 cm/45 (20.1") "A" Type 98 (?)
Updated 27 May 2012

The last two ships of the 1942 Naval Construction program were to have been battleships of about 90,000 metric tons armed with either eight or nine 51 cm (20.1") cannons.  After some study - and perhaps a dose of reality - these ships were redesigned as slightly larger Yamato class ships armed with six main guns in three twin turrets.  These ships were never officially ordered and all plans were destroyed at the end of World War II.

There is little information available for these guns, but at least one or two were being manufactured at Kure Navy Yard in 1941.  Construction would probably have been similar to the 46 cm (18.1") guns used on the Yamato class.  All development on these weapons was halted just prior to the start of the Pacific war.

Type 98 (1938) is my estimate, but they may have been Type 94 if their breech mechanism followed that of the 46 cm guns..


Battleship Design A-150
Detail from a painting by Richard Allison
Scanned from "Battleships:  Axis and Neutral Battleships in World War II"

Gun Characteristics
Designation 51 cm/45 (20.1") "A" (Kô Hô) Type 98 (?) (Model 1938)
Ship Class Used On A-150 Class (Warships # 798 and 799)
Date Of Design about 1938
Date In Service N/A
Gun Weight 223.4 tons (227 mt)
Gun Length oa 927.6 in (23.560 m)
Bore Length about 900 in (22.840 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume N/A
Rate Of Fire about 1 - 1.5 rounds per minute
Type Bag
Projectile Types and Weights APC - 4,190 to 4,409 lbs. (1,900 to 2,000 kg)
HE - 4,097 lbs. (1,858 kg)
Bursting Charge APC - 67 to 70 lbs. (30 to 32 kg)
HE - 186 lbs. (84 kg)
Projectile Length N/A
Propellant Charge 1,058 lbs. (480 kg)
Muzzle Velocity N/A
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
Note:  The propellant charge was in eight bags.
Mount / Turret Data
Designation Twin Turret
  Design A-150 (3)
Weight  2,736 tons (2,780 mt)
Elevation -5 / +45
Elevation Rate about 10 degrees per second
Train about +120 / -120 degrees
Train Rate about 2 degrees per second
Gun recoil N/A
Loading Angle N/A
Data from
"Naval Weapons of World War Two" by John Campbell
"Battleships:  Axis and Neutral Battleships in World War II" by W.H. Garzke, Jr. and R.O. Dulin, Jr.
"Japanese Cruisers of the Pacific War" by Eric Lacroix and Linton Wells II
Special help from Nathan Okun
Page History

09 October 2006 - Benchmark
27 May 2012 - Updated to latest template