It appears that when calculating the penetration for the 381 mm shells, the CBC component was mistakenly left out.
By taking the known velocity at 10 km and inputting it into the calculator without selecting the CBC option, we arrive at the same penetration value currently used in-game, 598.27mm at 10,000 m (see picture with data, “table 1”) and (see picture without the cbc option, “pen 10km no-APCBC”)
However, when properly accounting for CBC, the penetration becomes 664.75 mm (see picture with CBC option on, “pen 10km”) at 10,000 m, thus resulting in an overall higher penetration value at all ranges.
Also Using the 771mm pen at 1000m, assuming the APCBC box wasn’t ticked, reversing the Jacob de Marre formula I get the speed of 820m/s at 1000m. Double checking with the aforementioned speed of 820m/s, looking at the attached figures (see picture “pen 1km no APCBC”), we can reasonably assume that probably the APCBC option in the calculator wasn’t ticked as we in fact get (rounding) the 771mm currently in game, which in turn gets to 856mm if we tick the APCBC box (see picture, “pen 1km”)…
I attached pictures with the calculation at 15km too, with and without the APCBC box ticked, to further my hypothesis that during the calculations the CBC component of the shell wasn’t accounted for, in fact we get the number 516,62mm of pen which is close to the 517mm of pen at 15km currently in game.
sources for the table with velocities at different ranges:
Naval Weapons of World War Two by John Campbell, 2002 edition, Page 321
shell specifications :
caliber: 381MM
Weight (kg): 884.8
Speed (m/s): 850
Weight of explosive mass (kg): 10.16
