Since the beginning of the 70s, a technological race has started between the designers of increasingly efficient passive sonar, and the manufacturers of submarines, who sought to produce more and more discreet submersibles. ie radiating as little noise as possible of mechanical or human origin. Gradually, anti-submarine warfare saw the famous "bang" of active sonar made famous by many films, replaced by high-sensitivity hydrophones, increasingly powerful computer signal processing algorithms, and the famous "golden ears", awkwardly put in the spotlight in the film "Le chant du loup". In recent years, however, and the arrival of new submarines of almost absolute discretion, such as the British Astutes, the American Virginia or the French Suffren, passive detection has sometimes reached its limits, and if we know more or less than a submarine lurking around, the information gathered by passive sonar is insufficiently precise to determine a firing solution against the adversary.
Under these conditions, the only alternative is the use of the good old active sonar, which emits a powerful sound pulse to listen to the echoes, and thus determine the exact position of the target. If the use of an active sonar also reveals the position of its origin, the arrival of towed helicopter sonar, and even more new active-passive acoustic buoys, in particular allows a frigate to find the opposing submarine without having to to reveal its position. Obviously, the discretion of the submarines, even when pushed to its limits, today appears insufficient to guarantee the safety of the ship. It is in this context that the world champion of conventionally propelled submarines, the German TKMS, undertook to design, as part of the German-Norwegian program of cooperation around of the model Type 212CD, a new submarine that would not only be discreet, but also stealthy.
Concretely, for the German engineers, it is a question of relying on a technology similar to that used for stealth planes like the F-117 or the F-35, namely to try to alter the direction of the sonar echo. returned once it hits the submarine's hull. For this, and as in the aeronautical field, it is necessary to disregard these beautiful curves which formed a submarine, to replace them with plates sized and oriented so as to return the sonar signal in a direction that does not allow the transmitter to receive it and therefore to locate its target. Immense constraints are then applied to the design of the ship, particularly in terms of shapes, materials, but also size, so as to be able to effectively alter the signal over its entire wavelength, and not only over part of it. of it. And in fact, the Type 212 CD, which in many respects deserves its own name, will be 17 meters longer, 3,2 meters wider and 1000 tonnes heavier than the Type 212A currently in service with the German Navy, an increase tonnage of nearly 65%.
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