workmen, in spring 1941. Ten days later, while the Iyeda system was being tested, Naval Engineer Noma invented another system. It functioned in a similar way, but with a different mechanism. During the prototype tests, Noma's system was found to be the better, having less time lag in its responses. So the Noma system was adopted for the next production version of Type91 and it went into final testing in August 1941, making practical the use of aerial torpedoes both in rough seas and in shallow waters. It enabled the Type91rev.2 to run under water no deeper than 20 meters, with experienced pilots learning to launch their torpedo so as to sink to a depth of no more than 10 meters. Increase in explosive weight The anti-rolling controller also made it possible for the Type91 to carry a heavier warhead. The Type91rev.1 warhead weighed with a high explosive charge of , but the rev.2 warhead weighed with of high explosive. Warhead rev.7, which was carried by twin-engine bombers, weighed and boasted a high explosive charge of ; this was designed to pierce the reinforced armour plates of the latest US Navy ships. Main components (Type 91.rev.2) Warhead Length = When a torpedo hits a ship, the inertia forces the initiator to thrust forward and ignite its high explosive. The high explosive in the warhead will not detonate unless initiated as designed. An aerial torpedo, released at an altitude of 100m, is falling at nearly Mach0.5 on water entry and receives over 100G at the hard impact on the water surface. The Type91 warhead had five reinforced bands on the front-bottom of the inner shell, lap welded in the shape of cut lower half star, or the superposition of the letterT and the letterΛ. Air chamber L = The air chamber is a thin-shelled cylinder made of nickel-chromium-molybdenum steel. This tough steel alloy was originally developed for the steel armor plate of battleships. The chamber is charged with highly compressed air at , which burns with fuel oil to produce the driving power. Its pressure drops to around while running . Front float L = The front float section has a pure water tank, a fuel oil tank and a depth meter. The depth meter is placed at the bottom of the section to detect the water depth. It detects the displacement level and controls the horizontal tail rudders' (or elevators)'