Shallow Water Warfare in Northern Europe

 

 

Antisubmarine Warfare: The main problems of the shallow water environment are varying salinities, sea surface conditions, currents and tides, the variety and abundance of marine life, and the unpredictable effects of sound reflection and absorption by differing sea bottoms.

In the areas we are dealing with, the influence of water pressure can be neglected. Furthermore, in the shallow water areas of the Dutch and German North Sea coasts, the southern part of Heligoland Bay, and the Dogger Bank, only negligible temperature layers are encountered in the course of a year. The reason is the strong current which mixes the water masses of these sea areas down to the very bottom twice daily. There is only negligible difference in the amount of salinity between the surface and the bottom of the sea. As a result, vertical sound propagation speeds throughout these areas are either homogeneous, or the differences occurring are so slight that they have scarcely any effect on underwater detection. The dif­ficulty that does arise in shallow-water ASW comes about from strong sonar equipment reverberations re­sulting from the sea bottom, echoes from numerous wrecks, and other false contacts.

Considerably more problematical for underwater detection are the shallow water areas of the western Baltic: Belts, Sound, Kattegat, Skagerrak, and the

northern North Sea. Each year, approximately 1,700 cubic kilometers of Baltic water flow through the openings into the North Sea. The loss of water due to evaporation is roughly balanced by that received each year in rainfall. From inflowing rivers the Baltic receives only about 480 cubic kilometers yearly, apparently less than the outflow. The Baltic water flowing outward on the surface, however, causes an inflow of North Sea water near the bottom. The latter has a high salt content, is therefore heavier, and thus flows under the colder, but less salty Baltic water. This water flowing into the Baltic amounts to 1,200 cubic kilometers yearly. In addition to the considerable differences of temperature occurring be­tween the surface and the bottom of the sea, the speeds of sound propagation in these sea areas are very strongly influenced by the occurrence of salinity layers and frontiers which produce poor sonar condi­tions. Here, even under normal conditions with average water depths of 30 meters, a strong gradient of salinity occurs about halfway down. The salt content on the surface varies considerably from that on the sea bottom. Thus, there is a maximum change in the speed of sound propagation of 26 meters a second, certainly significant where sonar detection is concerned. The boundary layers occur­ring between the saltier, warmer North Sea water

and the less salty, colder Baltic water extend accord­ing to the time of year and the weather situation" from the Skagerrak as far as the Bornholm and Gotland basin.

The measuring procedures currently in use are not adequate for acquiring this boundary layer between differing sound velocities and thus not capable of including it in the forecast of sonar ranges. Bathythermographic readings should be taken far more frequently in shallow waters than in deeper portions of the ocean, because the conditions may change more quickly. Moreover, current bathyther­mographic measurement provides only some of the information needed and only for a short time in a relatively confined area.

The Limitations of Sonar Equipment: The conven­tional sonar sets in use in the Federal German Navy cannot penetrate through the layers in the Baltic, Kattegat, Skagerrak, and North Sea. Particularly dis­advantageous in the use of modern, powerful sonar sets in shallow water is the inability to adjust the performance. The very strong reverberations make sonar detection, particularly at close range, almost impossible. It is, however, especially important to be able to detect subsurface threats at ranges less than 2,000 yards under the oceanographic conditions de­scribed.

A special problem is the afternoon effect which results from the daily interchange of temperature between the atmosphere and the water. The condi­tion manifests itself in a clearly defined thermocline with very low sonar range. In offensive ASW exer­cises, the periscope of a submarine can sometimes be identified optically only a few hundred yards from the submarine chaser while detection of the sub­marine by means of the sonar equipment is not possible at all.

Some navies in Northern Europe, for example the Dutch and British, use variable depth sonars (VDS). But apart from the indisputable fact that these sonar sets are somewhat expensive as secondary equipment, they do not provide a 100% reliable solution for our sea area. Undoubtedly, when lowered beneath the thermal (sound velocity) layer, they result in a con­siderable increase in the detection range, but their usefulness would nonetheless remain confined to the somewhat deeper areas of the Skagerrak and northern North Sea. In shallow areas, the damage and loss arising from contact with the bottom would proba­bly not be justifiable from the point of view of cost-effectiveness. The decisive disadvantage in the use of variable depth sonar in the North European waters, however, is still the inability to determine

sound propagation speed accurately, obtain mathematically correct measurement data for detec­tion equipment and/or weapon control systems, and thus be able to engage the target with the greatest possible accuracy.

ASW Weapons and Modification Needed: It is not the intention here to dwell further on the effectiveness of short-range weapons such as Hedgehog or depth charges. But it cannot be denied that these old- fashioned weapons are sometimes still worthwhile, especially when gaining contact at very short range and using them as a quick reaction system to force the attacking submarine onto the defensive. The rocket launchers now in use by most navies have proved their worth, and further range increase pre­sents no great difficulty in light of the present state of technical development. However, the absolute destruction range of the rockets—as in the case of depth charges—is less than 15 meters and the dam­age distance less than 50 meters. Herein lies the problem: the weapon control system must be supplied with absolutely accurate range data, which in turn can be obtained only by the input of the

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exact sonic speed into the sonar set.

On the operational research side, the Federal German Navy is at present considering the idea of firing a rocket which would not be filled with explosive. Rather it would act as a sonar buoy and be fired to a position in front of any submarine con­tacted by ship-mounted sonar. This rocket would locate the target and transmit the target data by radio to the submarine chaser. The surface ship would then employ her own rocket weapons—or better, flying depth charges—against the target. It is true that here, too, the correct sonic speed is not taken into consideration, but in this case the sonar source is nearer to the target, and the errors in regard to the accuracy of bearing and range would be smaller.

The employment of antisubmarine torpedoes in shallow water areas is still in the course of develop­ment. Some U.S.-supplied torpedoes, originally de­signed for deep water, are now also to be employed in shallow water. But here as well, the many prob­lems connected with the redesign are by no means all solved. Apart from this, some torpedoes like the Mark 37 or Mark 44, with their relatively low speeds, their short maximum ranges, and their dis­appointing sonar characteristics in shallow water, can only be regarded as interim solutions. The ASROC (antisubmarine rocket) system, it is true, delivers the torpedo more quickly and over a greater distance to the opponent, but the great depth to which the torpedo dives precludes its use in waters less than a certain depth.

Moreover, all of the antisubmarine torpedoes available at the present time share the disadvantage that their runs cannot be corrected once they have been fired. A decisive step forward may be made when the new German antisubmarine torpedo now being developed goes into production. This high­speed, long-range torpedo, suitable for employment in shallow waters, is wire guided and is thus capable of being influenced from the time of firing until the target is acquired.

There are a number of possibilities for improving the effectiveness of antisubmarine warfare in shallow waters.

►Range Prediction Methods: The sonar range predic­tion tables now being used are either applicable only to deep water or to a specific piece of sonar equip­ment. What we need is a sonar atlas based on temperature and salt content. There should also be range tables for shallow water, and as far as possible they should be related to the types equipment in use and should take into consideration damping and ground interference.

In the documentary material (nautical charts, ta­bles etc.) in use by the Federal German Navy there are at the present time no special ASW charts with an indication of wrecks lying in its probable area of operations. With the use of a modern sonar atlas, the wrecks could be projected onto the ASW plot and thus indicate to the antisubmarine officer in good time that the sonar contact about to occur is a wreck or other bottom feature lying on the ship’s course or nearby. Such a special chart would be of inestimable value in shallow waters.              ■

►Special Equipment for ASW Ships: The good old bathythermograph has two important disadvantages. It records only temperature, and it considerably hampers the maneuverability of the ship while it is

being used. These are minutiae, which, under war­time conditions, place an unnecessary strain on the captain’s nerves.

The expendable bathythermograph, introduced into some navies, overcomes the lack of mobility during the measurement operation, but it still pro­vides no information about salinity of the water. The answer to the problem would be an expendable sonic speed measuring device which would not affect ma­neuverability. Admittedly, this device will not be cheap, but it should be used only in addition to the bathythermograph. In areas where the salinity is always constant, the use of the bathythermograph should be sufficient. In areas where the salinity changes, the expendable sonic speed measuring de­vice should also be used.

There is a further problem in connection with antisubmarine warfare in shallow water areas which should not be left unmentioned at this point—that of correct classification of contacts. Technology has, in the past few years, brought about further im­provements to detection means, weapons, and weapon control systems. Future technology advances will undoubtedly continue to help NATO navies improve both the recognition of the atmospheric conditions and their processing in the equipment. Unfortunately, technical aids to classification have developed very little since 1945. It is due to the many years of experience that ASW officers have in offensive antisubmarine operations in our area that wrecks, ground returns, and other frequently occur­ring false contacts have been promptly and correctly recognized. Combat morale and operating efficiency were thus not subjected to additional strain.

► Maritime Patrol Aircraft and ASW Helicopters: The

Minesweepers of the Standing Naval Force Channel: FGS Paderborn (M 1076), HNLMS GemertfAI 841), BS Venders (M 934), HNLMS Hoogeveen (M 827), and HMS Kirkliston (M-1157)

modern maritime patrol aircraft like the Breguet Atlantic or the Nimrod, flown by several navies in northern Europe, are equipped with outstanding means of detection. They enable patrolling of a wide area, rapid initial detection, and immediate employment of weapons. Due to the depth of water and proximity of the coast, however, some means of detection and weapons can be used only to a limited extent, or not at all. In the foreseeable future, however, we cannot dispense with the patrol planes’ help in shallow water offensive antisubmarine opera­tions, particularly in regard to classification, because not enough operationally effective ASW helicopters are available. A helicopter such as the British Sea King—whether based afloat or ashore—equipped with radar, sonar, and weapons offers all the advan­tages of combined offensive ASW operations in shal­low water areas and would release the maritime patrol aircraft to more fitting hunting grounds. The dipping sonar of an ASW helicopter has all the advantages of the variable depth sonar. At the same time, it eliminates to a considerable extent the disadvantage of inaccurate measurement data, since the helicopter can change its position with the least possible delay and approach to a minimum distance from the target without endangering its own safety. Rapid initial detection and immediate application of weapons—or action as consort for the weapon con­trol system of the submarine chaser—make the helicopter the most deadly enemy of the hostile submarine.

Conclusion and Outlook: At the present time, offen­sive ASW operations in shallow water areas of the North Sea and Baltic approaches are extremely prob­lematical. Failures predominate both in regard to location as well as in pursuit and engagement of targets. This requires improved equipment for sur­face antisubmarine units. Their needs have been summarized in the preceding paragraphs. It is also essential that a large number of modern ASW helicopters carrying radar, sonar, and weapons be employed in countermeasures against submarines in shallow waters. Even the best equipped ships cannot be successful if forced to operate alone.

To solve these problems in the future, scientists, technicians, and wide-awake politicians with an eye to the needs of antisubmarine warfare must work hand in hand. When dealing with offensive ASW operations at sea, one often hears the word “team­work.” It should never be forgotten, however, that effective cooperation in maritime operations must start with the teamwork of the three sectors just mentioned.

The Importance of Mine Warfare for NATO Navies: This subject is important in the shallow waters of the North Sea and Baltic because of the threat by the forces of the Warsaw Pact and by the special suitabil­ity of shallow waters for minelaying and mine coun­termeasures. Therefore, the defense mission of the neighboring NATO nations must also be oriented to this importance.

Mine warfare is the overall function of developing, producing, and laying mines according to a coordi­nated strategic plan with simultaneous efforts for the development, production, and handling of all types of mine countermeasures and means for engaging the enemy in mine warfare. The importance of the mine as a means of naval warfare may be summarized into five principles:

► The mine can influence enemy operation plans. A mine threat will restrict the possibilities of naviga­tion in oceans; this applies to both enemy and friendly forces. If ports have to be closed and ship­ping has to be rerouted due to mines, the logistical support channels become longer, and general war planning is influenced. Mines laid in shallow waters force ships to select greater water depths. There they come into the attack range of submarines and air­craft. Mines laid for defensive purposes can prevent a nation’s shipping from being hampered by the enemy.

► The employment of mines will force the enemy to take countermeasures. These measures against mines require a lot of ships, material, personnel, supply, and organization. At the end of World War II, for example, 40% of the German Navy was engaged in mine countermeasures.

morale. Mine detonations occur without warning and force ships at sea to keep their crews at a constant state of readiness—one which inevitably produces strain. The result is that the mental powers of resistance will decrease in the long run.

► The mine is of specific military-political impor­tance. The mere contention that mines have been laid may have the effect of an escalating factor at the beginning of a contest. Egypt’s contention, in the prelude to the Six-Day War of 1967, that mines had

► The employment of mines will affect enemy

been laid in the Gulf of Aqaba, was also one of the factors that led to war.

^ The mine has a serious disadvantage. Once the mine is laid, it is out of one’s control. It demands care at the beginning of hostilities or in times of tension.

Of these principles, the advantages of minelaying actions can become effective only if we succeed in laying minefields consisting of mines with the cor­rect tactical adjustment, in the right place, at the correct time, and undetected.

This aim of minelaying actions is confronted with the mission of mine countermeasures. The means and procedures of mine countermeasures seek to obviate the mine threat. If successful, then one’s own naval forces and shipping will be able to carry out their missions with a considerably reduced risk within mined areas or those which are threatened by mines.

The aim of mine warfare (minelaying and mine countermeasures) is influenced by a great number of single factors, which in their interdependence deter­mine the efficiency of this element of naval warfare.

The following factors are of particular importance when planning minelaying operations in the shallow waters of the Baltic and the North Sea:

► Target Ship Data: The fact that the Scandinavian and German Navies operate in the same area as the Warsaw Pact Baltic Fleet and part of its Northern Fleet ensures that NATO possesses a good knowl­edge of possible target ships in the event of a conflict. It is known what ships ply what waters, what degree of importance attaches to them, and whether their mission is likely to take them out of the Baltic.

► Mines: The shallowness of the North Sea and the Baltic, especially near the coasts, permits the use of every type of mine; it is only in the mouths of rivers flowing into the North Sea that silt sometimes prevents the use of blast mines, as sanding up does in the Baltic. The proximity of mine depots to areas of operations makes it possible to lay mines—which are always kept ready for use—in a matter of hours.

► Minelayers: The only minelayers suitable for opera­tions to close off the Baltic Approaches, due both to geographical circumstances and to the considerable threat from surface ships and the air, are small, fast boats which can take cover among the islands and which have powerful artillery to defend themselves to a large extent in the course of their operations when no covering forces are available.

► Tactical procedures: The confined space of the Danish islands, an area of operations particularly well suited to minelaying operations but difficult to navi­gate, the interplay between cover forces and minelayers, and the necessity to carry out operations quickly, all make mature tactical procedures neces­sary for minelaying.

► Political and Military Decisions: Sea denial opera­tions in the Baltic Approach area are of no military value unless they are carried out in time, which is to say before enemy vessels, in the event of war, have passed through the approaches or brought them under their control. Early political consent and military decisions are therefore necessary. On the other hand, a minefield, once laid, cannot be elimi­nated, and can, in the decisive preliminary phase of a war, exercise a disproportionately escalatory effect. Those who plan minelaying operations have to live with this contradictory state of affairs.

A few basic rules have to be observed in the North Sea and the Baltic in planning countermine operations as well:

► Limits on and Possibilities Open to Countermine Re­sources: Depending upon the expected mine threat and navigational conditions—and above all else de­pending upon the depth of water involved—the most suitable of a range of sweeping equipment has to be used: for instance, solenoid sweeps in river mouths, minehunters in sea areas with hard sandy beds, or cable-towed combined magnetic and acous­tic sweeps in the open sea. The German Navy possesses such an assortment of sweeps, so that it is in a position to deal with both the specific geo­graphic conditions obtaining in the North Sea and the Baltic and any and every expected mine threat.

► Route Planning and the Time Factor: In the event of war, shipping in the North Sea will be confined to routes from the very beginning, so that the potential danger of a theoretically unlimited minefield is re­duced to a minimum, the risk being artifically restricted to as narrow a lane as possible. All the same, the length of a mine-threatened route through the shallow waters of the North Sea is so great that the NATO Navies have to keep available a consider­able capacity in countermine measures. In the Ger­man Bight alone, there are some 400 nautical miles of routes and courses. The length of the routes and restricted countermine capacity calls, in considera­tion of timely resupply and reinforcements, for meticulous convoy planning and the concentration of countermine resources along the paramount routes and in the most threatened areas.

► Tactical Procedures: The selection and skilled han­dling of the most precise navigation procedure is an important prerequisite, especially in the North Sea with its strong tidal current and poor visibility, to economical minesweeping. Furthermore, an exact knowledge of the environmental factors attaching to the area to be swept is important: minehunting maps with bed echoes plotted in, tide and current charts, and the results of research into the salt content of the water, its electric conductivity, and sound propaga­tion conditions.

These factors will become standing, known, or pre­sumed elements in the sequence of planning, decision-making, and giving orders. The better and earlier these factors are quantified, the greater will be the degree of efficiency of naval warfare.

The Threat: The Soviet Union demonstrates every day that it meets the three requirements of a naval power: a strong fleet, a strategically important geographical position, and a maritime way of thinking. This espe­cially applies to the Baltic, where the Warsaw Pact has stationed naval forces, the strength of which is four times that of the NATO nations. For the maintenance and supply of the Soviet fleet, the Baltic is of the greatest importance. The naval bases in the Arctic Ocean, Black Sea, and Pacific are of secondary importance.

The former Chief of Staff of the Federal German Navy, Vice Admiral Gerd Jeschonnek, mentioned in a 1971 presentation, “The Federal German Navy and her duties today and in the 1970s,’’ given to the Staatspolitische Gesellschaft at Hamburg among others about the naval warfare potential of the Warsaw Pact Powers:

“The Soviet naval warfare would be impaired con­siderably if the Soviets failed to utilize the war

potential in the Baltic for the overall warfare. Thus,

the possession of the Baltic Approaches gains in this conjunction importance for the allied warfare all the more since the route from the Baltic bases to the Arctic Ocean bases via the Arctic Ocean Channel can only be used during the ice-free season, and it is easy to block. From statements of Soviet politicians and measures of the Soviet Navy it can be seen, that it is still the aim ofSoviet politics, also to achieve superior­ity in power in the Baltic area, which would offer a wide range of possibilities for negotiations to the Soviet leadership.”

Operational Areas: British, Dutch, Belgian, German, Danish, and Norwegian Navies operate in the North Sea, the Baltic, and the Baltic Approaches. Of all maritime areas of the world, those mentioned are the best suited for minelaying because of their normally low water depths. The water depths seldom exceed 30 to 40 meters (about 100 to 130 feet) and it is in the shallow water where shipping dominates.

For the main types of mines a water depth of at least 6 meters (about 20 feet) may be presumed as the lower employment limit. Moored mines within the coastal waters of the European area are bound to a maximum depth. Bottom mines may be employed in water depths up to about 60 meters (about 200 feet). Thus, all normal main shipping routes in the North Sea and the Western Baltic now meet all requirements for mine warfare, so that all types of mines must be expected in these waters. The routes which are being used are generally the shortest connections along the coast and, therefore, they have very shallow water, and are focal points of ship­ping. For this reason they are especially suitable for minelaying.

Mission: The threat by the naval forces of the Warsaw Pact nations and especially by the Soviet fleets in the Baltic and in the Arctic Ocean requires the utilization of all possibilities of naval warfare within the scope of the NATO defense mission. It is, therefore, the mission of the allies to protect the northern flank of Europe and thus the maritime boundaries of the NATO territory in Europe against attacks from the sea. In defensive opera­tions against attacks at sea and from the sea, the land and air forces of the allies will have to be in close cooperation with the naval forces.

In order to carry out this mission, minelaying opera­tions play an important role as an effective element of naval warfare against the threat of a potential enemy. The use of mines is, of course, also especially favorable to the enemy, as our operational areas mainly consist of shallow waters, which have unlimited suitability for laying both contact and influence mines. Mine coun­termeasure forces must be able to quickly and strongly react to such threats too.

Future Requirements: In order to overcome the threat of the potential enemy and to be able to carry out their missions, NATO naval forces have the following principal requirements for minelaying op­erations:

►Mines whose firing systems evaluate all physical remote effects of ships. They cannot be swept on account of this feature and thus are very effective.

► High-capacity minelayers which are capable of high speeds

► All necessary technical and tactical data for the employment of minelayers and mines.

And mine countermeasures forces urgently need:

► The optimum assortment of countermeasures in order to effectively counter all types of mine firing systems and the existence of large quantities of mines. By this, the best geographical distribution should be taken into consideration.

► All technical and tactical data for the employment of countermeasures. Both elements of mine warfare must have knowledge of the influence of the en­vironmental factors within the maritime area and of the potential enemy. Strategic and political princi­ples should be taken into consideration.

At present, the NATO navies are partly at the beginning and partly in the middle of a moderniza­tion phase of their forces. When the program for the modernization of the Federal German Navy was developed, it was based on the three following prin­ciples within the assigned maritime area of the NATO alliance:

► The lower the expense for defense, the more time is required for countermeasures and thus, the more important is the utilization of the depth of the defensive area. This depth of the defensive area exists in the Baltic and within the adjacent maritime areas assigned to us.

^ Naval warfare has three dimensions—under water, on the surface, and in the air—and in none of these dimensions may the enemy remain unengaged. This would prevent the enemy from concentrating its effort against only one weapon system.

^ Therefore, the efficiency of the defense at sea is based, similar to that in land warfare, on fighting with combined weapons. These form a system in which no weapon may be missing. Otherwise, the efficiency of the whole action will be affected.

The mine as a means of naval warfare is especially suitable for the direct defense in the depth of the defensive area. The risk of casualties to friendly forces is low. Nevertheless, the mine serves the many purposes described above. Thus, ranging from a dummy minefield up to minefields consisting of activated mines, minelaying operations offer the pos­sibilities required by the political leadership for controlled escalation and crisis management. Only the fact that the NATO naval forces are in the possession of mines contributes to a credible deter­rence.

The minelaying capacity (almost all surface forces and submarines are suitable for minelaying opera­tions) of the Warsaw Pact powers and the low water depths within the operational areas of the Federal German Navy are probably the cause for a mine threat in case of a conflict. Therefore, the potential enemy must also be engaged under water. In order to ensure the mobility of our fleet, the combined mine countermeasures weapons must not be absent during a fight. Therefore, minelaying operations and mine countermeasures as means of naval warfare will keep their important positions within the future modern­ized and balanced fleets of the NATO navies.

Conclusion: From the presentation of the primary importance of mine warfare and the problems of practical antisubmarine warfare in shallow waters, it can be seen that these very different fields of naval warfare show a few important common characteristics which are due to the peculiarities of the northern European shallow waters. Knowledge about the en­vironmental factors within the operational areas is of decisive importance for both antisubmarine warfare and minelaying operations and especially for mine countermeasures.

Commander Salitter graduated from the Federal Ger­man Naval Academy in October 1958 after joining the Navy two years earlier. His sea service has been primar­ily in destroyers and frigates as antisubmarine warfare officer. After graduating in 1966 from a one-year career ASW course at Eckernforde, he served in the German Destroyer Flotilla as staff ASW officer. After two years as director of the German underwater tactical weapon trainer, also in Eckernforde, he became executive officer of the Fletcher-class destroyer Z4 (DD-178). He has been to the United States for ASW courses at Key West, Great Lakes, and Norfolk and made a three-week cruise in the USS Claude V. Ricketts (DDG-5) in 1970. Since 1975, Commander Salit­ter has been aide to the acquisition manager of the new frigate F-122 in the Ministry of Defense at Bonn.

Commander Weisser was commissioned from the Fed­eral German Naval Academy in 1959. Following initial tours afloat as watch officer and in command of the coastal minesweeper D'uren (M-1079), he served in the Minewarfare Section of the General Naval Office and as a branch chief at the Underwater Weapons School. Commander Weisser was a student in the Admiral Staff course at the German Armed Forces General Staff and Command College at Hamburg from October 1971 to October 1973. Since then, he has been assigned to the Ministry of Defense in Bonn.