Sweden's Gotlands Are Ready for Fleet Operations

By Commander Fredrik Hallström, Royal Swedish Navy

The submarine is divided into two watertight sections, one forward and one aft, separated by a small passage that includes a one-man escape chamber. Swedish submarine rescue policy stipulates that it should be possible to save the crew with a rescue vehicle in the event that it is forced to the bottom in an accident. The back-up rescue method is free ascent, highly effective to depths down to 600 feet, which is well in line with depths in the craft's primary area of operation. The entire interior and all inboard equipment has been mounted on rubber sound-insulation mounts in order to meet tough impact-resistance and noise-reduction demands. This design results in extremely low noise output, at the same time ensuring that the craft can handle the shock of most weapon impacts.

The conning tower is used primarily when running on the surface, as a navigation and control center for the officer of the watch. It also houses a number of masts and the forward elevators. The only mast that penetrates the pressure hull is the periscope.

We enter the forward compartment through the mess, which accommodates 12 people. This is a common space for everyone on board, from the commanding officer to the seamen. In the adjacent galley, the cook—-a conscript doing his military service—prepares three meals a day. Adjacent to the mess are the heads and berthing spaces: three four-man cabins, one two-man cabin, and the commanding officer's cabin. A double watch system (six hours on, six hours off) is customarily used in the Swedish Submarine Service, which necessitates hot bunking. Since the non-watch personnel, the CO, the marine engineering officer and the cook have their own berths, a total of 27 men can be accommodated in the cabins. Others, such as trainees, are given temporary berths in the torpedo room during peacetime. The level of comfort in the cabins is high by submarine standards. The watch schedule provides stability and has made it possible to reduce the crew size to 25 men; a three-watch system would require approximately 35 men.

The torpedo room is located under the cabin interior. It contains torpedo tubes, reserve torpedoes, and all the electronics required to monitor and fire the weapons. The forward storage battery is located beneath the reserve torpedo positions. The craft has four tubes for 20.9-inch torpedoes and two for 15.7-inch torpedoes. Two 15.7-inch torpedoes can be loaded into each tube. These are used primarily for self-defense, but also can be used in ASW. The big tubes accommodate either a Swedish-type Type 613 torpedo or a Type 42 self-propelled mine. Ready for action, the torpedo room is manned by two men. Everything is hydraulically operated, resulting in extremely rapid reloading.

The control room is located on the main deck, abaft the mess and living quarters. All essential tasks relating to control of the craft's movements, action information organization using various sensors, and technological monitoring of the craft are carried out here. The chart table and associated equipment, including a depth sounder, logs (passive and active), radar, plus Global Positioning System (GPS) and inertial navigation systems, are at the forward end of the room. A navigation computer distributes all necessary data to users such as the fire-control equipment, sonar system, etc.

Pursuant to Swedish standards, a control panel on the port side forward controls the X-configured aft control surfaces and a forward elevator on the conning tower. Everything, including the trim and weight compensating systems, is served by one helmsman, who can also control the thrust produced by the engine/propeller combination. A single man can thus control the submarine's course, depth, trim, and speed. The system provides excellent control properties, which are needed when evading antisubmarine warfare threats and navigating underwater in coastal archipelagos.

Abaft the helmsman are panels for ship-control technology. Submersion and surfacing, drainage of keel ballast tanks, and the hull valves and tanks are controlled here. This is also where damage control and rescue services are overseen.

The new SESUB 940 combat direction system consists of three consoles located in the control room, one of which is devoted to integrated electronic support measures (ESM). The overall system is used to evaluate target data and for fire control of torpedoes and mines. Most of the input data comes from the sonar system, although ESM, periscope, and reconnaissance data also are taken into account in evaluating targets. A newly developed target-motion analysis algorithm provides the target-evaluation factors—course, speed, and distance—quickly and with a high degree of precision. SESUB can evaluate a large number of potential targets concurrently.

The Gotland class is equipped with a CSU-90 sonar system with cylindrical, flank, and intercept arrays, served by three general operator consoles. The decision not to equip Swedish submarines with towed-array sonar was made on the basis of testing carried out during the 1980s. The test results showed that, with today's low self-produced noise levels, adequate results could be achieved with flank-array sonar, which does not compromise the submarine's control profile, sea-bottom performance, hovering, and regular turning ability as does a towed-array.

The control room is separated from the passage by a pressure-tight bulkhead. All safety equipment is stowed in the passage. There is a one-man escape chamber above the passage, and outside it there is a platform for access by rescue vehicle.

Abaft the passage is the Stirling space, which is what differentiates the Gotland class from all other currently operating conventional submarines. The compartment is 33 feet long and contains two Stirling engines with generators and accessories. All liquid oxygen and nitrogen required for operation of the Stirling engines is stored here. Each generator can develop 75 kiloWatts of power—which can increase significantly the time between snortings. The submarine's batteries may even be charged when hovering. In normal use, however, the extra power makes it possible to patrol an area at low speed for weeks without using the batteries, which can be kept fully charged.

Abaft the Stirling space is the electrical center (EC). The aft storage battery is located under the floor plate. It, and the forward battery, are controlled from here. Propulsion-control panels and electrical-conversion cabinets for power used on-board also are housed here, and the diesel engines are monitored here during snorting and battery-charging. All functions are highly automated, and can be operated by just two men, a machinist and a motorman, during normal operation. Farthest aft are the two diesel engines themselves, with direct-driven generators, propeller engine, and peripheral equipment such as compressors and hydraulic pumps.

The pre-delivery testing program was essentially the same for all the submarines. General tests that were deemed to be tests of the class rather than the individual craft were carried out on one boat only, usually the Gotland . After basic maneuverability testing, surface propulsion tests, log tests, and tests of safety features, underwater testing began: tests of leveling, maneuverability and propulsion at low speed, and snorting. A rescue exercise was then carried out by a test of free ascent from the escape chamber, from a limited depth of some 115 feet. Only then did deepwater testing and emergency blowing tests at maximum diving depth begin. Following deepwater testing and high-speed maneuverability testing, it was concluded that there were no special limitations to the use of the submarines.

The Stirling machinery, which was started on the first day at sea, was tested for long periods along with other systems. The added capacity this machinery provided impressed everyone involved in the project. It has made snorting such a rare event that crew members consider it something of a happening.

A basic principle employed in the testing and fine adjustment of weapons systems was to verify the functioning of all sensors before testing the functions of the fire control system. Only when it was ascertained that everything was working properly in concert were torpedoes fired. When the second and third submarines were tested, the torpedo tests were expanded to include tests involving guiding multiple torpedoes to different targets.

The introduction of an on-board differential global positioning system (DGPS) made significant contributions to both speeding up and improving the accuracy of testing. Since essentially the entire Baltic Sea is covered by DGPS, it was not necessary to concentrate testing to specific, geographically limited weapon testing ranges. DGPS data from both the submarine and target vessels, when used, were transmitted to a computer continually during testing, at the same time as data from the sensor being tested were recorded on another computer or in the fire control system. After mooring, all data were transferred to a simple computer and the results were analyzed.

Not surprisingly, not everything worked. A short chain of command and excellent cooperation, however, allowed us to solve most problems quickly.

Early on in the project, a decision was made to accept the risk of developing new software for the whole weapon system. A land-based facility including sonar, fire control, a navigation computer, a tube automation computer and various simulators was therefore included in the order. Work on integrating and debugging the various components of the weapon system had been under way for over a year before the Gotland spent her first day at sea. The land facility has since been modified and serves very well as a training center.

The class had a chance to show what it was made of early in the testing process, as the submarines were sometimes included in ordinary Fleet operations. The purpose of doing so was to gain valuable tactical experience. It would also provide a good indication of whether the requirements the Navy had specified for the class could be met.

There is always a risk involved when a new craft is subjected to early advanced testing. A serious failure early on could delay the entire project or, in the worst case, cause the future of the project to be called into question. The transitions between pure testing and tactical operations would not have been possible had the extensive preliminary and quayside testing program not yielded good results. Another factor is crew training, which was carried out concurrently with quayside testing. The excellent results of these tests quickly inspired confidence in prospective crewmen. Without the confidence of the crews, the new submarine would have been unable to switch back and forth in this manner. Things went quickly: the Gotland dived on her fourth day at sea, the Uppland on her third, and the Halland on her first.

In July, 1995, the Gotland cast off for the first time. By August, she was ready for her first cruise to a foreign port, Copenhagen, Denmark. A newly built Swedish sub had never been abroad so early. A submarine emergency rescue exercise was carried out in conjunction with the visit. The main elements of the exercise were tests of docking with a rescue vehicle and free ascent from the escape hatch. Both went off without a hitch.

Ten months after her first day in open water, the Gotland took part in the 1996 Exercise Sorbet Royal, held in Vestfjorden, Norway. She cruised from Malmo to Bodo underwater with Stirling power. Tough reliability, endurance, and seaworthiness demands were made of the not-yet-fully-tested submarine. It is worth noting that Kockums still formally owned the Gotland at this point. She passed the test with flying colors, and the crew gained valuable experience of autonomous long-term operation in the process. Participation in Sorbet Royal was a welcome break from the rigors of ordinary testing for the crew. The exercise included docking with the Swedish submarine rescue craft and the British LR-5, and free ascents by some Gotland crew members.

The resistance of the Gotland class to weapon impact was tested in the fall of 1996. Shock tests of new submarines are nothing new in the Swedish Navy. They have been carried out on all new classes since the Sjoormen . The submarine is moored to buoys and submerges. The crew remains on board. The explosive charges consist of scrapped torpedo warheads and mines that are suspended from buoys. The angle between the charges and the submarine is varied so that measurements and results can be collected for explosions in a full circle around the craft. According to tradition, it is the first submarine of a given class that is subjected to such testing. The Gotland stood up very well to the detonations.

The Uppland , which was subjected to basic testing at sea during the latter half of 1996, was ready for a series of tactical tests in 1997. She took part in applied tactical exercises under the direction of the Fleet. One test was intended to determine whether the submarine class could be resupplied after a mission in a coastal archipelago setting. The Uppland arrived at an anchorage in one of the many protected bays among the coastal islands, depleted of necessary supplies. In the course of a few hectic hours, she was resupplied with everything: rations, torpedoes, fuel, lime, LOX, etc. After the resupply, the submarine settled to the bottom, depth 45 feet, and recharged her batteries. This provided valuable resupply experience, particularly with regard to the handling of LOX at an anchorage and the order in which various supplies should arrive. The crew met the time requirements that had been established for resupply and battery charging.

In late 1997, the two submarines-in-testing, the Uppland and the Halland , participated in Tudor, an annual competition for the Fleet's submarines, consisting of rescue, sonar and craft recognition services, and firing torpedoes on an escorted target unit. The largest number of points is awarded for the torpedo firing contest. Extra points are awarded for long firing range and attacking with sonar only. Each submarine is provided with three torpedoes. The target unit consisted of three mine-laying ships escorted by patrol boats, coastal corvettes and helicopters. All the participating subs carried out sonar attacks and fired their torpedoes. The two Gotland -class craft were alone in hitting all three targets simultaneously with their three torpedoes, and the Uppland was named best submarine of 1997.

Even before they have been delivered to the Navy, the Gotland -class submarines have demonstrated a high level of reliability, endurance, seaworthiness and impact-resistance, and well-functioning weapon systems.

Commander Hallstrom , a veteran submariner who conducted the sea trials for the Gotland s, has served on virtually all of Sweden’s operational submarines. He commanded the Vastergotland .

 

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