armor thick extending below the main belt was included in the ships as a response to gunnery experiments upon and the new Japanese Type 91 shell which could travel great lengths underwater. Furthermore, the top hull shape was very advanced, the peculiar sideways curving effectively maximizing armor protection and structural rigidity while optimizing weight. The armor on the main turrets surpassed even that of the main belt, with turret face plating thick. Armor plates in both the main belt and main turrets were made of Vickers Hardened steel, which was a face-hardened steel armor. Main armored deck— thick—was composed of a nickel-chromium-molybdenum alloy. Ballistics tests at the proving ground at Kamegakubi demonstrated the deck alloy to be superior to the homogeneous Vickers plates by 10–15%. Additional plating was designed by manipulating the chromium and nickel composition of the alloy. Higher contents of nickel allowed the plate to be rolled and bent without developing fracture properties. For torpedo protection, a multiple bulkhead side protection system was used which consisted of several void spaces as well as the lower belt armor; the system has a depth of and was designed to withstand a TNT charge. No torpedo defense system compartments were liquid loaded, despite the known benefits. This may have been the result of overestimating the effectiveness of the lower belt armor against torpedoes, an effort to decrease draft, and provision of additional counter-flooding spaces. The relatively new procedure of arc welding was used extensively throughout the ship, strengthening the durability of the armor plating. Through this technique, the lower-side belt armor was used to strengthen the hull structure of the entire vessel. In total, the vessels of the Yamato class contained 1,147 watertight compartments, of which 1,065 were beneath the armored deck. The ships were also designed with a very large amount of reserve buoyancy to mitigate the effects of flooding. However, despite the immense armor thickness, the protection scheme of the Yamato class still suffered from several major design flaws and shortcomings. Structural weakness existed near the bow of the vessels, where the armor plating was generally thinner, as demonstrated by Musashi's damage from a torpedo hit in 1943. The hull of the Shinano was subject to even greater structural weakness, being hastily constructed near the end of the war and having been equipped with incomplete armor and unsealed watertight compartments at the time of her sinking. The torpedo defense