The Largest Submarine in The World, Sentoku

During World War II, Japan built Sentoku the largest submarine in the world. This class of submarine, which was also named I-400, had hangar constructed on the upper main deck to accommodate three floatplane bombers, Aichi M6A Seiran. The submarine was reported to be 60% larger than the largest American submarine. The Imperial Japanese Navy (IJN) ordered the construction of the I-400 submarine class as their secret weapons to destroy major US cities and the Panama Canal - the main route for the US to logistically supply their troops fighting against the Japanese in the Pacific. The Japanese had suffered great loss during the marine battles in Guadalcanal, and Midway as well as land battles in the Netherlands New Guinea island. It had been planned that the launching of surprised attacks on the Panama Cannal and US big cities would stop the US from immediately supplying their troops in that region thus providing enough time for the Japanese to consolidate and strengthen their troops.

Unfortunately for the Japan, the I-400 submarines could not fulfil their mission because the US had bombed Hiroshima and Nagasaki with nuclear weapon forcing the Japanese government to surrender without any condition. Sentoku and her sisters submarines could carry aerial torpedoes, three 800 kg bombs and twelve 240 kg bombs to arm their Seiran aircrafts. The propulsion of this submarine was powered by four 3,000 hp engines with enough fuel to travel around the world 1.5 times.

The propulsion system of submarine

The propulsion system of a conventional submarine is designed to meet two different operating condition. The first one is when the submarine is moving on the surface of the water and the second one when it is moving under water.

If it is on the surface the resistances it has to overcome are the same as those of conventional surface ships. There will be water (frictional and wave making resistances) and some air resistance. If the submarine is operating under deep water it will not face wave making resistance. Due to greater wetted surface, the submarine will have greater frictional resistance.

Every submarine has been designed and constructed to operate in three dimensions. It can move forward, diving, and manouvering to the right and left sides both on the surface or under water. To have such abilities, a submarine will need not only rudders for moving on horizontal planes but hydroplanes for controlling depth.

When moving on submerged condition, a submarine needs to be fitted with Air Independent Propulsion (AIP). The diesel-electric scheme is the most common form of the submarine propulsion system. Diesel engine will be used to propel the ship if it is on the surface but electrical drive supplied by batteries will be needed to propel the submarine when it moves underwater.

Often submarines need to operate in longer period of time underwater especially when encountering enemies. This operating condition needs highly efficient batteries that can provide greater and longer endurance. In the past, naval architect decided to equip such submarines with nuclear power plant.

Now other alternatives such as closed cycle diesel engines, fuel cells and Stirling engines are being developed. Actually, diesel engine is not an ideal choice for a submarine due to its toxic fumes which can harm the ship crews. Therefore, efforts to improve the efficiency and size of the batteries are now being carried out to increase the overall performance of the propelling system of the submarine. by Charles Roring in Manokwari of West Papua