HMS GOTLAND -THE IDEAL SUBMARINE FOR THE LITTORAL AND OCEAN WATERS

February 2 at the Kockum’s shipyard in Malmo, Sweden, a new class of diesel submarines was launched and christened by H.M. the King as GOTLAND, named after the largest island in the Baltic. Sweden, using submarines in their naval arsenal since Stockholm built SHARK in 1904, has, like the U.S. Navy, maintained a more or less continuous development of submarines ever since. For instance, the years immediately after WWD, the Royal Swedish Navy wanted to evaluate the true experience of modem submarine warfare. As in many other navies, the German Type XXI class gave most of the inspiration for the submarine of the 50s, the Shark (Hajen) class, launched 1955-57.

Of course the Gotland class, like the other 12 Swedish subs now operating, are mainly designed for littoral, and even shallow-er, waters with acoustically disturbed water conditions as is the case in the Baltic and the western approaches to the Swedish coast.

However, with the new UN and NATO policy, Partnership for Peace, which the Swedish government has fully accepted, Swedish weapons can be deployed far away from own coast. This may mean shallow or deep blue waters. The GOTLAND has been so designed. But let us first look at the boat itself.

The Boat

Gotland is a multi-purpose submarine for attack, surveillance, mining and ASW. It is developed from the Vastergotland class (as was the Australian Collins class), but with a better endurance and fit for autonomous and stealthy performance. More qualified sensor capacity and air independent machinery has resulted in a relatively larger boat, but by international standards it is still a small one.

GOTLAND is a conventional single hull boat with the pressure bull divided by a tank section into two watertight compartments. The forward upper section contains crews quarters, electronics room, galley, mess and the control room. The tank section is also used as a platform for the URF (DSRV) and includes the escape tower.

For safety and environmental reasons there is a special electronics room for vital parts of the weapon systems. A large part of the upper space holds the control room, which also contains combat information and fire control functions. It also contains the wireless center and ship technical, diving and maneuvering panels. On the second floor: forward torpedo room, forward battery, spare torpedo arrangements and auxiliary departments.

Most of the space aft is occupied by propulsion and Stirling engines as well as by ship technical functions. Before description of the propulsion system let us have a look at the boat’s main data:

• Displacement: 1500 tons {like the WWD fleet subs)
• Length: 196.8 feet
• Diameter: 20.3 feet
• Propulsion: Diesel-Electric, Stirling-Electric, skew-back propeller, speed 20+ knots (see below)
• Weapons: Tubes for heavy weight (21 “) and light-weight (16”) torpedoes and mines
• Complement: 25 (compare with the old fleet boats!)

Weapons, sensors, tactical displays, shock resistance arrangements and signature reduction techniques are of state-of-the-art technology and commensurate with modem threats. The entire design is characterized by cost effectiveness. The habitability standards are high, especially due to the small crew, automation and remote control of functions on board. Thus the crew’s quarters are divided into 2-or 4-man cabins.

The functions of the submarine platform are controlled, managed and monitored from three consoles, all incorporated in the ship’s monitoring system. The maneuvering control console contains:

• Course and depth control
• Equilibrium control (weight vs. displacement. Improved and very silent system.)
• Longitudinal weight balance (trim system)
• Main motor speed control.
• The diving and damage control console is also in the control room controlling;
• Diving and surfacing
• Snorkeling preparations and snorkeling monitoring (not very often used, see below)
• Monitoring and control of bull integrity.

It is very important that all automated functions have redundant controls. The ultimate operating mode is local manual control, which can be quickly engaged if a dangerous situation should arise. This is also applicable to the steering system which will be dealt with below under Steering.

The Combat System features the latest design and among other things, determines target positions and movements based primarily on sonar data for subsequent engagement by launching weapons and guiding them to target destruction. The major elements are sensors, processing units, presentation units and data transfer units. The system is capable of long range detection of targets.

Included in the system is the target motion analyzer (TMA), a function which determines position, course and speed of several selected targets. The new TMA function is optimized for bearing information only, which provides the means for determining target data purely in a passive and stealthy mode.

Instruments, computers and other equipment are not entirely of Swedish design. Subcontractors all over the word have been evaluated and those providing the optimum performance have been selected.

Weapons

The principal weapon system for the Gotland class is the new heavy weight torpedo (Torpedo 2000), produced by Bofors Underwater Systems in Motala, Sweden. It is a high-speed, long-range weapon with a unique thermal propulsion system. The Tp 2000 calibre is the well proven 21″ and it is a homing torpedo with a wire communication system between the torpedo and the fire control system.

The GOTLAND is also equipped with the new Bofors light weight multi-purpose torpedo, Torpedo 43X2, the result of a continuous development from the first homing ones of 1965.

Incidentally, the first torpedo purchased in 1875 by the Royal Swedish Navy was a 14″ torpedo from the inventor-Robert Whitehead’s factory in Fiume, Italy-but since 1910 all torpedoes have been designed and manufactured in Sweden.

Propulsion

The propulsion system consists of two energy producing diesel motor generators (MTV) as well as an electric propulsion motor. Storage of energy is accomplished, by normal means, with two accumulator batteries.

The Swedish Navy has had a productive cooperation with the French electric firm Jeumont Schneider and their subcontractor Merlin Gerin for some years, the latter is a specialist in making the main switches and control systems. The motor system is totally computerized, has a fault finding computer with printer at the control panel and all equipment is designed for quick and easy maintenance within easy reach. Needless to say it is a very silent system.

Ships’ service power is provided either by the diesels or, from GOTLAND’s captain’s point of view, more importantly, by the Stirling machinery. The Stirling engines give energy to the boat’s power economy and also to the generators when operating at low speed.

The Stirling system consists of two 4-cylinder Stirling external combustion engines-with one generator each. The engines run on diesel oil, and instead of air-injection, oxygen is used. The oxygen is in liquid form and is stored in tanks, so called LOX-tanks. The stored oxygen has a temperature of minus 1620C, which is why the LOX-tanks are well insulated.

More than six years ago the Navy installed the first test Stirling engine in the submarine NACKEN, which had to be extended 45 feet in length. Although it is a quite new concept for submarine use, it has functioned extremely well, therefore it was a rather easy decision to make it a standard on the new constructions.

The fighting value of NACKEN, GOTLAND and their successors has increased to such a degree that you can say it is doubled compared to other diesel submarines. Another compari-son is that the Stirling motor section in the boat represents the same amount of energy as five submarine batteries, while no reduction of other energy sources have been made.

Why did the Royal Swedish Navy choose the Stirling system in the first place? There are, as surely is well known to the SUBMARINE REVIEW readers, other AlPs under development in Europe. The Stirling engine is a very old concept, in fact it was the invention of a Scottish priest in the middle of the 19th century. Adopting it for submarine propulsion is the fruit of 40 years hard work.

The Swedish Navy realized in the middle of the 50s, when USS NAUTILUS and her successors had shown the new way of pushing submarines forward, that a type of AlP was necessary for the submarines of the future. It soon became clear for the Baltic waters that an AlP design was preferable to a nuclear design, for obvious reasons. One of the first attempts started was to develop a diesel engine of a circular motion type (in German: kretslauf). The safety problems turned out to be rather difficult, although a propulsion plant in full scale was running in a Swedish laboratory.

Next, the Navy invested in fuel cells and the large firm ASEA in middle Sweden-nowadays ABB (ASEA Brown Bovery)-started to work on this concept. Many problems arose and in the end it was decided that the fuel cell was not the cost-effective solution the Navy was searching for.

In 1987 Kockum-Stirling presented an AlP that was, as is mentioned above, installed in the submarine NACKEN. It became a success from the very beginning. At this writing, Stirling AlP is the only one operating in a commissioned submarine anywhere in the world.

Steering

The maneuvering and steering system with an X-rudder is something that the first Swedish Albacore shaped submarines of the Sea Serpent class had. The first one was launched in 1967. The main principle of the X-rudder system is that all rudder planes are working in any maneuver in all dimensions, thus giving the maximum steering effect. This is especially valuable when operating in very shallow waters, when it is possible and necessary to steer by inches from the bottom.

In fact Kockums obtained the original idea from the Albacore’s X-rudder, which, however, was constructed for extremely high speed. The test results of USS ALBACORE in 1962 proved this configuration to be far superior to anything previously tested in way of rudder arrangements concerning maneuverability, heel angle and emergency maneuvers.

However, by this time the U.S. Navy had already built and launched 15 SSNs and 11 SSBNs all based on the Albacore hull form, but without the cruciform rudder arrangement. It is supposed that under these circumstances there would seem to be little point in changing the designs, but perhaps if the test results had been available a couple of years earlier it is probable that all nuclear submarines would have had X-rudders.

Vice Admiral Emery, COMSUBLANT, says in his paper from the NSL 1994 Symposium that, in order to minimize depth excursions from control surface casualties, when SSNs are operating in littoral waters, they should be fitted with split stem planes, obviously a good solution for the cruciform rudder systems. For the Swedish, and also the Dutch Walrus submarines, the X-rudder system gives, as the Swedish Navy thinks, the ultimate solution to that problem.

Kockums has had the system under continuous development since the Sea Serpent class with some cooperation first by ASEA, later by the SAAB Aircraft Inc. and for the GOTLAND by the Dutch firm van Richtschoten & Houwens. All three firms delivered a sophisticated steering panel (SAAB also provides that for the Collins class submarine).

When talking about these steering arrangements one special question naturally comes up: safety! What happens when one or more rudders fail for some reason as in a depth charge attack? Does the system then collapse? Or what happens when the computer gives up? In case of failure, the X-rudder system can quickly be engaged in a manual control mode, where it is possible to handle each rudder separately. There are also other safety devices with several hydraulic systems and it is possible to maneuver the boat from the steering panel by using only two rudder planes.

These different safety systems in the Swedish submarines are often exercised in damage control drills and, after nearly 40 years of experience, the crews have full confidence in the reliability of this steering system. On GOTLAND the rudder planes are made of plastic (GRP) to a special Kockum design. Additionally, these rudders are more robust to shock, and simpler to maintain. The constructor is Karlskronavarvet AB, shipbuilders of a large number of warships, in later years many of them of GRP. Detonation tests against the GOTLAND type rudders have been successfully made.

Deployment and Operations

The Baltic is an inland sea and represents a limited area with short coast-to-coast distances, easily surveilled by sensors ashore, at sea, and in the air, as well as by electronic and communications intelligence systems. For national security reasons, this sea has always been an important area and war theater for the countries concerned.

Through the centuries Britain, Russia, Germany and Sweden have tried to control some sort of Mare Nostrum in the Baltic. When Russia moved her positions westward to the coasts of the Baltic countries, Swedish defence policy planning immediately reflected it and a particular stress was laid on certain areas of Sweden. Today there exists some sort of military calmness and, in a way, some state of stability in the Baltic.

Although Sweden, like most other democracies, is cutting its defence budget, it is the consensus of the Swedish people that it is advisable to keep a certain guard for the future, like getting and keeping weapon and defence material that will take a considerable time to provide. Examples are aircraft, tanks, missiles and submarines. The last named are especially suitable to keep a sharp guard on what is going on in the Baltic and the Western surroundings

Here the environment for submarines is very favorable because the rocky bottoms along the Swedish and Finnish coasts make specific conditions for acoustic propagation extremely favorable. The lack of strong currents and tide permits very high navigational accuracy for submarines. Also the lack of really rough weather permits a very accurate depth control close to the surface. This is necessary during summertime in order to get a good covering layer.

Thus ASW is very difficult in the Baltic mainly because of the acoustic propagation and bottom conditions, but also because of the anti-ASW threat. Performing ASW operations with surface units in the Baltic in time of war is dangerous due to aircraft and submarines. However, definite underwater contacts from under-water craft have been established on several occasions in the hunts for foreign intruders in Swedish waters during the last decade. The submarines were and are important parts of the special ASW task forces. Using the best instruments and devices that money can buy, considerable experience has been gained in ASW in the Baltic. Recent R&D has established new knowledge of propagation in the Baltic.

The last decade’s development in sonar technique bas led to increased ranges for submarine passive detection, especially in the Baltic. Passive ranges in the Baltic against cavitating surface targets exceeds 100 NM. In the archipelago, however, the ASW is different and much more complicated. Equipped with the new long range guided and homing torpedoes these submarines represent a very potent attack component in the Swedish defence forces. That is why in the budget cutting process the 12 submarines continue to survive.

Modem Swedish submarines are all equipped with the latest sonar sets such as flank array sonars (F AS) and cylindrical hydrophone array (CHA) as well as sensors and sets for own noise and enemy sonar search.

The sonar system is the most expensive and complicated system onboard. This places large demands on the construction of the boat, and explains why considerable resources and engineering have gone to create the most cost effective submarine system.

Also much work has been done to make this submarine more quiet than before. Many old and new methods have been developed, such as double elastic fitting or a i>split suppressed bottomplate, and more effective liquid sound suppressors.

Long range surveillance with the possibility of a heavy surprise punch gives the Swedish Navy the opportunity for forward deployment at an early stage of a conflict. An enemy cannot move out of his bases without being detected by the submarines, reported and, if necessary, attacked without knowing from where or by whom.

To reach this type of total surprise will in a considerable way be the fruit of the new long endurance submarines.