pressure, just when such a feature was more essential. In the USN, the South Dakotas had a similar arrangement but they were designed within stringent Treaty constraints, a worry Yamato's designers did not have. In the US Montana class, a planned vessel of similar dimension to Yamato, the holding bulkhead was placed much deeper and not tied to the belt at all.



This late adoption of a thicker, lower bulkhead caused a new problem: how to join it to the main belt above without jeopardizing the great inherent strength of either half. The solution, as can be seen, was far too flimsy and relied for its transverse strength, which would be tested most in a torpedo strike, on the shearing resistance of tap and three-ply rivets. This was toprove the Achilles heel of the system.



The percentage of explosive force which would break on this flawed main defense did not rely only on the volume of the intervening outboard space. The composition of this space could be significant, and in all Yamato's foreign contemporaries part or all of the outboard void was tilled with liquid, generally fuel oil. This was not a fire risk and since it was incompressible it could spread and reduce the shock of any explosion, and in addition diminish the danger from splinters. The Imperial Navy were well aware of this system and thought liquid layers next to the main bulkhead were the best type, but like the Royal Navy, their primary teachers, they also experimented with using closed steel tubes which were