Here appears to be the source of this image. Per there:
THAT is a section of turret armor plating that was slated to be fitted aboard the IJN Shinano. As the Shinano was converted to an aircraft carrier, the turret armor was never fitted. The test was conducted in October 1946, with a 16/50 Mark 7 gun firing a super heavy AP shell. The tests were conducted at point-blank range. Had the armor been inclined back at the 45 degrees as planned, it would have been impenetrable to guns of any caliber at any range, bar point blank. Read more over at the NavWeaps Technical board.
The Final Comments section of that page states:
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!!!
OobeBanoobe on October 21st, 2021 at 18:36 UTC »
If only they had built it with 27-inch thick armor.
JustSamJ on October 21st, 2021 at 18:44 UTC »
That's metal
Spartan2470 on October 21st, 2021 at 19:36 UTC »
Here appears to be the source of this image. Per there:
The Final Comments section of that page states: