SILENT HUNTERS Even the sensitive ears of a sonar cannot hear it: The Class 212A submarine, built in Kiel since 1998, moves undetected underwater, where it performs reconnaissance missions, acquires an overview of the situation, or releases frogmen near the coast. TEXT NILS SCHIFFHAUER PHOTOS PATRICK OHLIGSCHLÄGER ANCHORS AWEIGH! U-31 can set sail from the dock in Eckenförde at any time and even cross the entire Atlantic underwater – largely undetected 26 DRÄGER REVIEW 120 | 2 / 2019 MILITARY SUBMARINES COMMANDER Timo Cordes in the engine room of U-31. He is in charge of a fl eet on which he can rely – and vice versa even though “it looks like the door to a bank’s safe,” accord- ing to the then commander Lars Gössing. “I had never experi- enced anything like that before. It was testing.” Equally as test- here on earth are the Germans?” The participants ing was the 18-day underwater record trip from the Azores to W in a navy maneuver in the Caribbean, in which U-31 also took Jacksonville, Florida. part, asked themselves this question. It is the pride of the Ger- man Navy and one of the most modern non-nuclear subma- AS SMALL AS A COLA CAN rines in the world. “We were only 300 meters away from them,” Life for the team of almost 30 submariners is hard; each of them recalls frigate captain Timo Cordes in the officers’ mess of his is an expert in his or her field – from sonar to mechanical engi- moored submarine off the coast of Eckenförde. “A distance neering. Furthermore, a keen sense of comradeship is required. that classes as a near miss!” This way of traveling, as if under “Tolerance is one of the most essential virtues,” says frigate cap- a cloak of invisibility, is just one of the outstanding features of tain Timo Cordes. “Sailing in a submarine unquestionably calls the Class 212A submarine that has made it an export hit over for teamwork. The crew soon notices who isn’t suitable, despite the years. That said, the technology and crew must also play their qualifications, and also tells it like it is!” Not just anybody their part. “We are the only ones who can safely pass through can be assigned to a submarine. You have to want to do it and the Kadetrinne area in the Baltic Sea, north of Rostock, which also be accepted. “It has been my dream since the eighth grade,” is precipitous and only 17 meters deep.” says First Petty Officer Zörner, explaining his choice, which often Chief Petty Officer Hans-Jürgen Zörner, responsible for the takes him away from his family for long periods of time. They extensive machine systems on U-31, nods – and remembers that live in the Harz region and are waiting for his next shore leave. far from being always calm at sea, it can also be pretty rough At sea, he is practically cut off from any kind of private commu- at times. “In a Force 12 storm, the 56-meter-long and seven- nication, particularly the Internet. meter-wide vessel rammed against waves eight meters high “On a submarine, if feels as if you are not in this world.” while traveling on the surface of the water. The maximum per- Instead, you are drawn into a world that is dominated by six- missible inclination (“listing”) of 45 degrees over a longer peri- hour watches. The fact that the crew is prepared to accept this od of time was even slightly exceeded – risking a breakdown hardship is one thing. But why does a country even maintain of the diesel engine that charges the batteries when traveling a fleet of submarines when each one costs over 400 million on the surface. It even ripped out the door to the cold store, euros, with development costs of 150 million, plus operating DRÄGER REVIEW 120 | 2 / 2019 27 MILITARY SUBMARINES DREAM REALIZED Hans-Jürgen Zörner wanted to be a submari- ner ever since the eighth grade. The chief petty offi cer is now aboard U-31 THE SONAR PROVIDES ACOUSTIC IMAGES OF ALL SHIPPING TRAFFIC costs? And why doesn’t Germany have any nuclear submarines? able acoustic and thermal signature with its reactor and the “This is due to the role assigned to modern submarines in our necessary steam turbine.” primary areas of operation in the North Sea and Baltic Sea,” explains the commander. Although equipped with six torpedo SIMILAR TO A STEALTH BOMBER tubes, their main task is to remain undetected while obtain- The Class 212A is built at thyssenkrupp Marine Systems in Kiel, ing a reliable picture of the situation on the surface of the which boasts a history totaling more than 180 years following water and swiftly passing it on as part of the overall situation. the merger with HDW and Blohm+Voss Naval and the acquisi- In this regard, the passive sonar is the submarine’s eyes and tion of Atlas Elektronik. Germany’s first submarine, U-1, was also ears. Water is very good at conducting sound, allowing all of built by a predecessor of this company in 1906. Today, around the unavoidable noises emitted by shipping traffic, primarily three submarines are built in two years in Kiel. “One and a half the propeller, to be heard across long distances. “Low frequen- per year sounds a little odd somehow,” says production manag- cies in the infrasonic range – below 20 hertz – travel particular- er Frank Mallon, while pointing out the modular technology at ly far,” adds Timo Cordes. “As such, a modern sonar allows us the shipyard. “Space is very tight in the submarine. As such, we to hear when just a single valve has been operated somewhere generally produce the modules complete with all the cables and outside.” Combining these sounds produces the “signature” of conduits before installing them in the pressure hull.” It is much a vessel – or its acoustic image, to be more precise. This is so like the approach used to make a ship in a bottle, albeit one that individual that it not only identifies individual types of vessels, weighs around 1,500 metric tons. Top-quality German engineer- but each vessel itself. ing is in demand, taking about five years from the order to the The submarine can chart the traffic on the surface of the delivery. Almost everything in these halls is secret – from the water by changing its position and taking bearings – based sonar and the tubes for the fiber-optic cable-guided heavyweight on the principle of triangulation – to determine the location, torpedoes (with a diameter of 533 millimeters) on the bow to the course, and speed. The situation is then passed on via the Cal- propeller on the stern, the shape and number of whose blades listo radio buoy tied to a towing line, generally by satellite. Two- primarily produce the acoustic signature of the submarine. way radio traffic beneath the water is not possible. However, The propellers developed and built here almost entirely avoid even diving submarines can be reached using very low frequen- cavitation – small and loudly collapsing vapor bubbles. And the cies, like those emitted by the German Navy via eight anten- sides – with their flank array sonar, which features high sensi- na masts, each around 353 meters tall. It goes without saying tivity even at frequencies as low as 10 hertz and good resolution that the vessel itself should have a signature that is as small as of ambient noises – are also a secret. We agree to accept that possible – acoustically, but also electromagnetically and ther- the pressure hull – the outer shell, made from non-magnetic mally. This is precisely the case with the Class 212A subma- steel, making it almost impossible to locate electromagnetical- rine, of which the German Navy currently has six. It is said that ly – is about “the thickness of a thumb.” How much pressure their signature is the size of a cola can, which is down to their can it withstand? A smile must suffice as the official answer, design. “A nuclear submarine, on the other hand,” explains because otherwise the maximum diving depth can be worked Timo Cordes, “not only has completely different strategic, oper- out, which is at least 250 meters. Enormous pressure is thus ative, and tactical tasks, but also leaves behind an unmistak- exerted on the outer hull, whose fiber-glass paneling scatters 28 DRÄGER REVIEW 120 | 2 / 2019 ENTRANCE AND EXIT Submariners usually call out “up/down ladder” prior to ascending/ descending. This is certainly no place for those who suff er from claustrophobia! THE JOURNEY MUST CONTINUE Everything is functional on a submarine. Its form follows the logic of hydrodynamics and inconspicuousness – mainly acoustically IT IS TIGHT HERE, REALLY TIGHT Every square inch is used in the submarine, more by the technology than by the crew members, who cohabit for weeks on end in the tightest of spaces. Safety is also assured by the emergency breathing air systems from Dräger in their orange bags, with which it is even possible to evacuate the vessel underwater DRÄGER REVIEW 120 | 2 / 2019 29 MILITARY SUBMARINES FRANK MALLON is production manager at thyssenkrupp Marine Systems in Kiel, where the fi rst German submarine was built in 1906 A POWDER STORES THE HYDROGEN FOR THE FUEL CELLS the pulses of a hostile active sonar in all directions. It is a tech- air to generate power, permit even longer dives. This principle nique similar to that used on stealth bombers. At the heart of is based on electrolysis in reverse: When their polymer electro- the submarine is the drive system.