U.S. Naval Proving Ground, Dahlgren, Virginia, Report #5-47, "Ballistic Tests And Metallugical Examination Of Japanese Heavy Armor Plate" (November 1947)

Test of 26" (66cm) Class "A" Main Armament Turret Face (Port) Plate, originally for IJN SHINANO, the third Japanese YAMATO-Class super-battleship (converted into an aircraft carrier, instead, and sunk on its way to final fitting out yard by a U.S. submarine), which made up far left side of turret face looking from inside turret out of gun port, with "D"-shaped cutout making up about half of left curved gun port forming center of long right side of plate.

Japanese Vickers Hardened (VH) face-hardened, non-cemented armor (used only on YAMATO-Class battleships.)

Average of two tests; measured from plate face surface directly into plate.

Hardness varied in smooth "ski-slope" curves between these points - at 0.75" hardness increase reversed direction abruptly. Back hardness varied from Rockwell "C" 11.0 to 15.5 in long undulations to back surface.

Steel had many tiny pieces of dirt and so forth, being about the same as pre-WWI British Vickers Cemented (VC) KC-type armor steel in quality (VC was used for the first time in the Japanese battleship IJN KONGO, built in Britain, and manufactured in Japan under license thereafter), from which the unique Japanese armors New Vickers Non-Cemented (NVNC), the homogeneous, ductile form of VH used in a number of Japanese post-WWI warships, and VH itself was derived (this steel was not up to U.S., British, or German post-1930 steel quality). Carbon content was raised above VC steel level to increase ease of hardening, some copper added to allow some nickel (in short supply in Japan) to be removed (but not much), slight amount of molybdenum added to increase hardenability still more, and the cemented (carburized) thin surface layer used in VC (and in most other, foreign face-hardened armors) was eliminated with no loss of resistance from VC quality (a good design point). Surface of plate face was very smooth, unlike rough, pebbly surface of cemented plates, such as U.S. Navy Class "A" armor.

At about 40,000 yards, the U.S. Navy 16"/50 firing a 16" Mark 8 Mod 6 AP projectile (the later Mod 7 and Mod 8 designs were post-WWII, so I usually do not count them and they were no better ballistically, to my knowledge) will hit at about 45° downward angle and 1607 feet/second (489.8 m/sec). Just as with a point blank hit at 2500 feet/second (762 m/sec) and 45° obliquity, this hit too will barely hole the plate as the projectile is hitting at 0° (normal) obliquity, though not completely penetrate it. Any slight barrel wear will lower the muzzle and striking velocities and no holing will occur at these or any other ranges, as mentioned. However, this is so far above any real fighting range (even with radar it is hard to see the target due to the earth's curvature interfering, especially in any kind of imperfect seeing conditions) that I do not even consider it in my computations, while putting the gun barrel up to almost touching the enemy turret is also a pipe dream in real life! Thus, no holing or complete penetrations, ever, though possibly some cracking of the plate and possible jamming of the turret if the crack-off plate piece is dislodged badly enough.

Therefore, these plates are the only warship armor plates that could not be completely penetrated by any gun ever put on a warship when installed leaning back at 45°, as they were in the actual turrets!!! Even to completely hole the plate all the way through at that inclination requires a brand new 16"/50 Mark 7 or German 38cm SK C/34 gun at point-blank range firing the latest versions of their respective AP projectiles; it might be cracked at a lower striking velocity, but no hole put entirely through it! And they said guns had completely overmatched all armor - not so!!!

31 August 1999

Updated.