I am afraid I have given you the values of tensile strength demonstrating that D steel cannot be considered even close to an armor grade steel, the same concept Mr.Wahl explained to you.
ST52 steel (the one used for mere hull plating of Bismarck) had hardness of 150 Brinell and tensile strength of 64kg/mm2.
Your own posted table shows hardness 160 Brinell for the best D-steels (vs 150 for ST52) and tensile strength of 78 (vs 74 for ST52) but you don't specify the measurment units used in the posted table, I guess the difference with my figures is in measurement units (metrics vs anglosaxon)
Please look at the values I have given you for the true armor grade steels above (e.g. the ones Germans used in WWII, all Krupp /nA (neuer Art = new type, much better than WWI ones).
Please, admit D steel could have been (possibly) considered armor grade in WWI, against soft cap WWI shells. By WWII, it was not much superior than a construction steel like ST52.
Also, according to the article of Mr.Okun you yourself have posted (http://www.navweaps.com/index_tech/tech-085.php
), a German WWII hard cap (Type II) shell cannot be de-capped with less than 0.12 caliber plates (around 45 mm for a 380 mm shell at 20° descent angle, in the table it is 70° obliquity, or 49 mm for 406 mm shell) and only hard cap Type I shells can be decapped with 0.0805 caliber (31 mm steel for 380 mm shells, 33 for 406 mm).
Therefore KGV weather deck was a splinter deck, not a de-capping deck. It could have slowed (very, very marginally) incoming large caliber shells, but it could defeat neither them nor their cap. Check yourself the values in the below table, please, if you trust Mr.Okun.