This paper addresses the German submarine technology and its evolution during the last 35 years. It concentrates on features integrated in the new submarine class 212 for the navies of Germany and Italy, like hydrogen/oxygen storage and energy generation by fuel cells, signature minimization, permanent magnet propeller motor, water ram weapon expulsion system. etc. The paper comments on the submarine-related maturity/suitability of different air-independent energy systems and the competitive situation of submarine designers and builders in Europe. It ends with information about the German submarine class 212 development, design, and construction costs.
Historical Background
The rearmament of the German armed forces, started in 1955, was subject to several political and technical conditions agreed upon between the Allies and Germany before that date and modified in the years thereafter and until the reunification happened. The conditions that were the origin of and reason for technologies and industrial structures and capabilities observed today in Germany have, to a large extent, been forgotten on both sides of the Atlantic.
The German Ministry of Defense (MOD) was not allowed to operate and control organizations, departments, institutes, or companies for research, development, design, and construction of arms of any kind, including, of course, submarines. All such work had to be subcontracted by the MOD’s purchasing department, which had to be exclusively manned with civilian governmental employees, to private industry.
For submarine-related research and development {R&D), Ingenieurkontor Luebeck (00.) was founded and operated by Professor Ulrich Gabler, who had experienced several war
missions on submarines during WWII as a chief engineer before he was called into the then naval design offices at Berlin for the design of the next types of submarines. Right up to today, the privately owned office ofIKL performs R&D and design work for all classes of German submarines for the MOD.
In 1969, the German MOD contracted Howaldtswerke-Deutsch Werft AG (HOW) as the lead yard/prime contractor for the turnkey program of 18 units of the class 206 submarines for the Federal German Navy (FGN). This program included not only the detailed design work, purchasing, and construction, but also the operation of up to four submarines in parallel during sea trials until the contractually specified performances of each boat and all its subsystems, including electronics and weapons had been proven at sea-culminating in several scenarios of torpedo firing exercises. Shipyards’ own crews accumulated driving experience and fed this experience back into the design offices of the same company, thus creating the unmatched technical maturity of the class 209 design.
The industrial capability of delivering submarines under agreed specifications for the overall weapon system became attractive to several nations and navies that could not establish or maintain a full submarine R&D and detailed design capacity of their own.
Other conditions accompanying the rearmament phase had a significant influence on the development and the performance of German-designed submarines. Most significant was the tonnage limitation to 450, then 1000, then 1800 tons standard, which is no longer in effect today. However, of broader influence on submarine design was the allocation of the Baltic Sea and the Baltic approaches as the operational area of the FGN. The average depth of 40 and the maximum depth of 90 meters triggered not only the nickname flooded meadow for this area, but also developments deemed useful today in regard to littoral warfare requirements.
Nuclear propulsion was not allowed for German submarines in those early days when everybody believed that the dream of submariners would become reality and remain affordable.
Resulting Submarine Design Particularities
The optimization of a fighting machine of small tonnage, allowed to be called a submarine (but only of 450 tons max), resulted in design principles best characterized by:
- Doubled use of spaces on board: for example, the living space was used also as a torpedo-reloading space and there was the hot bunk system (17 bunks for 23 crew); and
- Deletion of any weight allocated for functions that did not add to the fighting capability: as an example, the deletion of the torpedo loading hatch or the hull-mounted instead of deck-mounted fixation of heavy but shockproof equipment.
The necessary weight optimization also required the pressure hull to be designed and built to be as light as possible. The calculation methods applied had to be test verified. Consequently, the principle of scale 1: 1 testing was also applied to a complete bull of a class 205 submarine within a worldwide unique pressure dock of the naval arsenal at Kiel. This collapse test bad to prove that buckling of plates and instability of frames occur at the same outer load and that calculation methods and tolerances are in conformity with reality.
For coastal submarines, a shock and collision resistant steel with sufficient elasticity is the preferred choice. Mechanized production of high yield (HY) 100 hulls has been tested, but the application in designs offered is deferred until a customer insists on this material for his pressure hull.
All weight remaining within the maximum tonnage limitation after satisfying the requirements of sensors, data processing, manmachine interfaces, communications, weapons, propulsion, living conditions, etc. was used for energy storage and stability ballast. The German designs had between 16 and 24 percent of their surface weight in the form of active ballast which means battery. International submarine designs built so far achieve at the most half or two-thirds of this.
Not only the overall designer’s consideration of battery weight but also the battery manufacturer’s achievements in Whrs per Kg, or liter, of a lead-acid battery add to the performance/endurance/ speed hotel power. etc .. of a submarine. Today. with the introduction of various forms of energy storage and production for the power demand during deep submerged operation, using the power-per-ton ratio seems to be a more adequate way to compare the parametrical overall deep submerged energy content of different submarine designs. For instance, the British UPHOLDER and the Dutch WALRUS both are capable of about 5kW hrs per ton while the German 205/206/207 /209 classes do about 9kWhrs/ton.
The maximum energy made available onboard has never relieved the submarine design engineer nor the subcontractors in their joint task of minimizing the required energy consumption for mobility, data acquisition and processing, living, etc., or, in other words, finding continuously more efficient and even multiple ways to use energy in its different forms and temperature levels. A most welcome side effect is the minimization of thermal effects in the water.
Signature Minimization
For about 30 years the most important operational area of German submarines has been the Baltic Sea. These waters are shallow and dominated on the surface and in the air by the Eastern opponent, more than suitable for mines with any kind of fuses and for bottom-moored acoustic sensors. Besides radiated noise, color selection, radar cross-section of the hoistable installations, sonar cross-section, etc., the magnetic signature of the boats was an additional and unique requirement of the German Navy. This feature of a magnetic design and construction has been transferred to the class 212.
Technology Applied Today
The new class 212 is being built for the navies of Germany and Italy (Figure 1). The definition of the class 212, in U.S. Navy terms-the concept design, was finalized in July 1992. The construction contract, which includes in Germany the detailed design, was expected to be accepted in early 1993. The reshuffling of the federal budget due to reunification consequences delayed the signature of the contract to 1994 and the effective date of the contract to 1995.
The class 212 mission priorities are anti surface, antisub, and reconnaissance. These required a drastic increase in passive sensor ranges since surface targets as well as submarines have reduced their radiated noise levels significantly during the last decade. While passive detection ranges have more than doubled compared to submarines built a couple of years ago, the own noise radiation under comparable speed is now only a fraction of what it was. The 212 will displace approximately 1200 tons and be 56 meters in length. The power plant is a hybrid AIP fuel-cell plant with a diesel generator-battery base. Sonars will be an optimized flank array and a towed array. The propulsion motor is a permanent magnet motor with a low noise propeller.
The boat, as under construction contract today, has pressure hull diameters of 7 and 5. 7 meters.
Newly developed components of the boat are mainly the proton exchange membrane (PEM) fuel cell system, the permanent magnet propulsion motor (PMM), the towed array with low frequency detection and classification, several features of the combat management systems, and the torpedo launching system.
The hydrogen/oxygen fuel cell system was at sea on the class 205 submarine U1 during trials in 1988 and 1989. HDW gave a briefing to NATO attach~ in March 1989 about the results. The inherent safety of this system, the fully automatic operation, and the refueling from local suppliers of industrial gases in Norway and Scotland was proven during the sea trial period. The fuel cell used in the system at that time was an alkaline type fuel cell. In the meantime, the development of the PEM fuel cell has been completed. Its low temperature level and high efficiency, together with the potential of air breathing (replacement of charging diesels depends how fast costs can be brought down), made this type of fuel cell attractive for submarine application. An oxygen/hydrogen-consuming PEM fuel cell manufactured by Siemens will be installed on the class 212 submarines. In our hydrogen lab at HDW, hydrogen/air breathing PEM fuel cells made by Ballard in Canada are also being tested and prepared for submarine use.
The oxygen is stored in two liquid oxygen tanks under the superstructure while the hydrogen is absorbed by metal-hydride, consisting of a mixture of titanium and ferrum with several additional ingredients, which is in hard-mounted tubes fixed around the pressure hull. The direct chemo-electrical energy conversion process has a high efficiency rate. The waste heat is partially used for releasing the absorbed hydrogen from the storage pipes in gaseous form.
The prototype of the permanent magnet propeller-motor has been driving a naval trial vessel since 1989. The availability of more powerful solid state switches triggered a redesign phase that was completed at the end of 1992. The low rpms and high efficiency of this PM are achieved over the full speed range without mechanical switches and generation of transient noises.
The Hydraulic Water Ram system consists of a piston in a water-tilled tube pulled back by hydraulic force. The water column is led to one of three weapon tubes. The prototype of the torpedo launching system was fitted into a towable section and operated during sea trials for shock and noise tests. It is a hydraulic water ram system that accelerates the weapon to be launched in the quietest way and allows weapon launches even if the boat is bottomed. The class 212 submarine bas two water ram systems and six weapon tubes in total.
Other Design Features
The overall design of the submarine has been organized in a modular structure, both for technical reasons and for cost-efficient production. The CIC with its control consoles, etc. is arranged on a deck that is elastically connected to the pressure hull. Other electronic cabinets and complete storerooms, etc. are suspended under this deck without any uncontrolled noise-transferring contact to the hull.
Special emphasis was also given to the small but unavoidable noise of auxiliary engines, such as air conditioning, pumps, etc. They have all been fitted together in the encapsulated engine room, and their fittings and connections were optimized in regard to structure and airborne noise transfer to and through the pressure bull. Measurements were performed at sea on the engine room aft section of the submarine with critical equipment actually operating. The hull-mounted heavy hydrogen storage tanks were represented by corresponding weights.
Besides the noise signature, emphasis has also been given to minimizing the magnetic signature. The pressure hull is built of 1.3964 steel, an authentic magnetic and non-corrosive steel. The final compensation of a still remaining small magnetic effect (despite stray field-reducing design and magnetic materials used throughout) will require only a few kW, while for a boat of comparable size built of HY80 nearly 100kW would be consumed continuously without achieving the same signature reduction.
Class 209
Subsystems developed for the class 212 can also be adapted for integration into other submarines, for example into class 209 boats. The submarine class 209 has outnumbered every other nonnuclear submarine family in the western world, with SO units contracted by 11 different navies. These boats have been continuously updated upon availability of platform improvements or of new sensors and weapons. Even an increasing number of U.S. suppliers is considering these boats as a potential market for their products.
It has been investigated to which extent an improved performance in deep submerged range could be achieved by adding the fuel cell system in a section with relevant storage capacities of liquid oxygen (LOX) and hydrogen stored in a metal hydride.
The deep submergence cruising range can be extended to more than 2,000 nautical miles.
Also technical solutions introduced on the last copies of the class 209 have found their way, after further improvement, into the class 212. An elastically mounted frame is the foundation for the four diesel-generator sets of a class 209 and the auxiliary equipments. All together they are moved on the frame into the empty pressure hull.
Cooperation with Italy
The specified performances and signatures of the class 212 design made available via government to government channels have attracted the Italian Navy with the result that the national development of their S-90 project was stopped last summer. A Memorandum of Understanding (MOU) between the MODs of Italy and Germany was signed in April of this year. A corresponding industrial cooperation agreement between Fincantieri and the German Submarine Consortium (GSC) has been adopted, ensuring the identical configuration of these class 212 submarines of Italy and Germany.
This cooperation has already resulted in a few changes to the original design of the class 212, such as increased diving depth, lockout for command teams, and a docking facility for a deep submergence rescue vehicle (DSRV).
Both countries will have advantages and will save on nonrecurring costs.
Technology Trends and Competition
There is a surplus of capacities in Europe for the development and construction of submarines. However, the necessary turnover of about two submarines per year which would allow maintaining up-to-date R&D activities at the prime contractor and specialized subcontractor level is not achieved anywhere-the industrial base of a single country is export-dependent.
Since Europe cannot afford several parallel submarine developments for its own national defense purposes, in October 1994 during the international naval exhibition Euronaval in Paris, the GSC, with HOW as the lead yard, presented a derivative of the class 212 design, the EuroSub, for follow-on-construction by European NATO members for their own national needs. However, the national specialization in certain weapon systems and the overall reduction in European industrial defense capacities will require time during which export dependencies of the industrial base will continue to exist.
The Race for Increased Non-Nuclear Energy Density
Different air-independent energy storage and conversion systems are presently under development (Table 1).
Outer-air-independent thermodynamic energy transformation processes are used onboard and at sea: the Swedish Navy added to the submarine class A19 (export designation 1’96) two units each of the Stirling engine, consuming desulphurized diesel and oxygen. The next class of Swedish submarines has been planned with fuel cells onboard. In France, the Mesmer turbine system (a derivate of nuclear power plant elements) is under development to go onboard the Agosta 90 class submarines for Pakistan sometime after 2003. The companies Rotterdamse Droogdoclanaatschapeij, Netherlands, and Vickers in England are cooperating and trying to export their Moray class submarine design with a closed cycle diesel engine for air independent power generation. It is remarkable that the Dutch Moray and the French Scorpene submarine designs are partially and, respectively, totally funded by the relevant governments, although no national requirements have been announced.
The optimal results, considering all naval submarine performance and signature requirements, are expected to result from the fuel cell system. The energy amount carried onboard will increase another couple of times with the integration of reformers producing the hydrogen for the fuel cells out of methanol on board. In this technology area, commercially used fuel cells will drive down the prices and we will see applications on commercial vessels for clean energy generation in harbors. The same units will replace the charging generators carried onboard our submarines today.
Russia
The most interesting competitor in the international market is Russia. Any price is all right if paid in hard currency. But not only the relatively old Kilo is for sale; also the single bull, cheaper to produce, Amur class submarines (of a tonnage between 950 and 1850 tons) show interesting features. Fuel cell systems have been tested at sea and will be integrated on the Amur class.
Summary
Particular features and technologies applied in weapon systems and submarines have their reason and origin in sometimes forgotten political and/or economical circumstances. It seems worthwhile to stop the daily routine business from time to time and recheck the validity for today of reasons established yesteryear. Therefore my paper began with a short recollection of conditions under which the development of German submarine technology started.
The industrial base is eroding and the defense budgets are too short to ensure the survival of desired capabilities and comfortable capacities-this is heard in many counties. Economic considerations other than military ones very often form the basis for decisions.
[Hans Saeger was born in 1938 in Gelsenldrchen, Germany. He completed studies in electronics at the Technical University In .Aachen, earning a Diplom-Ingenleur (Engineering Diploma). From 1964 to 1971, he saw active military service as an electronics officer in DD 183, and in electronics and weapons for naval .Air Wing 1. He served several months from 1973 to 1984 as a reserve system officer for submarines. From 1971 to today he has been involved in torpedo development; as head of various departments in the naval ship building division of HDW; and finally as director of the naval division of HDW.Table 1. Current Technical Position of AIP
| Signatures | ||||||
|---|---|---|---|---|---|---|
| Status of developement | Energy conversion | Maximum temperatures | Efficiency | Noise | Heat | |
| Fuel cell | submarine proven | direct/no moving parts | 80’C | approx. 70% | noiseisses | low/belowed loop |
| Closed cycle diseael engine | submarine proven | indirect/combination | >400’c | approx, 30% | noise reduction expense | cooling water exchange |
| Stirling engine | submarine proven | indirect/combination | >750’c | approx, 30% | noise reduction expense | cooling water exchange |
| MESMA | not submarine proven | indirect/combination | >700’c | approx, 25% | noise reduction expense | cooling water exchange |
