The German Navy (Deutsche Marine) operates a fleet of advanced submarines. The current Type-212A were the first in the world to introduce fuel cell AIP (air independent power). Now two of a newer model, the Type-212CD will be added to the fleet.
As well as being over 10 years newer than the current boats, they are also much larger. This should bring with it improved capabilities, especially stealth.
The Type-212CD is a joint project between the German and Norwegian governments. The order for six submarines (2 for Germany, 4 for Norway) is worth around 5.5 billion euros. German shipbuilder Thyssenkrupp Marine Systems (TKMS) is working with a Norwegian partner, Kongsberg. The first boat will be laid down in 2023 and delivered to the Norwegian Navy in 2029. Meanwhile the German Navy should get its first boat in 2032.
Outline specifications published by TKMS show the size of the new submarine. It is much larger than the current Type-212A, with surface displacement increased by an incredible 65% from 1,524t to about 2,500t. Length is increased by nearly 30%, from 57.20 m (188 ft) to 73 m (240 ft). And the width is increased by nearly 50%, from 6.8 m (22 ft) to 10 m (33 ft). Height is also increased by 2 m (6.5 ft).
One of the driving factors for the increase in size is that the submarine is now enclosed in a large outer hull. This is shaped to reduce boat’s sonar signature. Other benefits from the increase have not been published. We can guess however that it might carry more weapons, have a second diesel generator, and be able to operate for longer. There are rumors of a vertical launch system fore the Norwegian boats, to be armed with the NSM missile. This is currently unconfirmed however.
There are two basic modes of sonar which the submarine might face. Active sonar is when someone broadcasts noises and listens for the echoes when they bounce off the submarine. Passive sonar is simply listening for any sounds emitted by the submarine, such as pumps, engines, even the flow of water over the surface. For years passive sonar has been seen as king of submarine warfare because it doesn’t give away the predator’s position.
However this is shifting. As submarines have become much quieter, the effectiveness of passive sonar has decreased. To detect the quietest submarines, active may be needed. Therefore, being invisible to active sonar can provide a tactical advantage.
Many submarines already use layers of special rubber tiles or patches, known as anechoic coatings, to reduce the amount of sound which is reflected back to the enemy. They do this by absorbing as much of the incoming sound as possible. While this tends to be moderately effective, they do not make the submarine invisible. The Type-212CD takes this to the next level. The flat sloping sides are the primary way it reduces its sonar signature, known as the target echo strength.
A regular submarine hull with a cylindrical in cross-section will reflect incoming sonar waves from almost every direction. A flat surface however, if larger than the length of the incoming sonar’s wavelength, will reflect the sound in a narrow beam. This is the same basic principle as used on stealth aircraft.
Naturally it is not quite as simple as that. The exact water conditions can affect the path that the sound takes. And the wavelength of the sonar is also a factor. However with extensive computer modelling TKMS will have been able to optimize the angles to make the stealth shaping work in the widest range of operational conditions.
The Race To Be First
Actually the Type-212CD is not the first submarine to be designed with a faceted outer hull like this. All the way back in World War Two, when active sonar was still in its infancy, German designers planned the Type- XXIX-H U-boat. This had basic angled sides and sail. It was never built however and, lacking the artificial intelligence available today, it is questionable how effective it would have been.
US firm Lockheed also experimented with similar sonar-stealth concepts. These are a by-product of developing the famous F-117A Nighthawk stealth fighter. Around 1980 they even proposed a stealth submarine to the US Navy which featured angled sides like the Type-212CD. But it did not take off.
More recently naval architects in several countries have explored these principles. Of note, several British BMT designs featured similar cross-sections, and there are some hints in other future designs. However it looks like the Type212CD will be the first to adopt it on any scale.