accordingly, so that the torpedo maintains level running under water. The horizontal tail rudder controller is operated by the rod connection mechanism from the depth meter in the front float section. The horizontal tail rudders are locked at their uppermost position while the torpedo falls to the water surface. Engine housing L = This section is exposed to incoming water to help cool the engine. It has a starter, a Chowaki or pressure regulator, a wet-heat chamber and a main engine. The starter starts controllers, one for vertical tail rudders, and another for roll rudders for anti-rolling in both side wing rudders. The pressure regulator is called a Chowaki or harmonizing system. It is a two-stage pressure regulator with twin pressure-tunable regulation valves. It steps down the pressure of compressed air at in the air chamber to a constant flow of high-pressure air at . While the air pressure is declining as the torpedo is running under the water, the pressure regulator feeds the constant high-pressure air to the engine intake aspirator and keeps the running speed constant at . The wet-heat chamber is made of heat-resistant steel. Type91 aerial torpedoes use a wet-heater engine like almost all other torpedoes in World War II. The general wet heater burning method drastically improved the combustion efficiency of torpedo engines. It burns a mixed gas of fuel oil and the high-pressure air with a spray of pure water in the wet-heat block to produce burning steam gas which is fed to the engine. The high-pressure fuel oil gas is burnt at a temperature of . The sprayed pure water mists into the combustion gas, which produces a vapour explosion, resulting in completely gasified fuel oil combustion. The main engine is an 8-cylinder single-row radial piston engine. A single drive shaft runs to the tail and the screws. The main engine is started when the torpedo hits the water. A thick safety bolt is inserted into the starter when the weapon is loaded on an aircraft. The bolt is pulled out from the torpedo when it is released and remains underneath the fuselage of aircraft. Rear float L = This rear float section has a machine oil tank, a rudder controller, an anti-rolling controller, and roll rudders on both sides. The machine oil tank is centre-mounted in the rear float section. The rudder controller is a general gyrocompass controlled system, which steers the