LEOK: Coupled Sonar Simulators (1972)

Summary

In 1972, the Royal Netherlands Navy implemented simulators as a solution to the challenges of training sonar personnel effectively and cost-efficiently. The simulators were established at the Submarine Combat School ''Zeearend'' and aimed to provide realistic training in detecting submarines and employing tactics during torpedo attacks. The design of the simulators needed to consider existing equipment, including trainers for sonar equipment aboard submarine hunters, frigates, and submarines, as well as a torpedo fire control system. The simulators allowed for individual training sessions and joint tactical exercises, enabling crews to compete against each other. The simulators were coupled to create an integrated training facility, with special consideration given to accurately simulating sonar sounds and ship movements. Additionally, a periscope projection setup was developed to allow for visual observation of surface ships. The construction of the simulators and integration of the equipment involved collaboration between various organisations.

 

Coupled Sonar Simulators (1972)

 
The Royal Netherlands Navy has long known the problem of how to obtain a good education and training of the sonar personnel at an acceptable cost. In 1972 part of the solution to this problem was obtained by using simulators. The simulators were set up at the Submarine Combat School ”Zeearend” (Sea Eagle) in Den Helder.

When detecting submarines from surface vessels, active sonar equipment is used. Its operation and the correct interpretation of the information obtained require a great deal of practice. In addition, the tactics of a ship in a convoy during torpedo attacks or when fighting the submarine are very important.
The use of sonar and the tactics of the submarine itself are completely different. It is important to be able to operate inaudibly and invisibly. This sonar is therefore not equipped with a transmitter: it is a passive sonar. Even a radar may not be used while sailing with the periscope above water is dangerous. A training program in which the submarine crew can compete against the crews of several surface vessels has a stimulating effect. Simulators allow practising such a situation at the Submarine Combat School.

Determining factors in the design

In the design of the simulation equipment to be built for this Submarine Combat school, the existing trainers had to be taken into account. These were:

1. LAN/UQS trainer by Sangamo for sonar equipment aboard a submarine hunter.
2. Netherlands I trainer by van der Heem for sonar equipment aboard a frigate or submarine hunter.
3. Netherlands II trainer by van der Heem for sonar equipment aboard a frigate or helicopter.

The expansion had to include, among other things:

1. A simulator for sonar and radar display on board a frigate.
2. A simulator for sonar equipment on board a submarine.
   The periscope image also had to be presented.

Further requirements were:

1. It must be possible to practice with each trainer separately. However, to practice tactics in a convoy context or when jointly attacked by a submarine, various links between the trainers must be possible.
2. During these joint tactical exercises, each ship must be piloted by a helmsman who receives his orders from his submarine officer who is present at the plot table of that ship.
3. The sonar measurements and ship movements of the entire convoy must be visible on these plotting tables.
4. The sailing characteristics of the various ships must reasonably correspond to those of the actual ships.
5. To have an overall game leader who can comment during or after the exercise, there should be a Main Instructors Panel on which, among other things, all courses and speeds are visible. A sizeable vertical plot screen is used to display all ship movements on which all ships, the simulated torpedo and the simulated helicopter are projected.
6. An extensive internal communication system must be present, as is also the case on board ships.
7. The submarine will be provided with a torpedo fire control system from Hollandse Signaalapparaten (HSA). This torpedo must be heard on all sonar installations.

The financial benefits

If you want to practice against a submarine in the same convoy, then some 600 people are needed. The outward and return journeys need to be deducted from the total time so that even if the weather is good, the exercise yield in hours will always be low. In addition, the costs of this crew, the depreciation of equipment and the costs of training torpedoes are very high. The investments in simulators are therefore quickly earned back. However, it is not enough to just practice on simulators. The situation on board a swaying ship with wind force 10 and a seasick and overtired crew with an immediate threat of war is simply challenging to imitate in a simulator.

The simulators

Each sonar trainer consists functionally of a calculation part and a sonar (sound) generator. The sonar sound is so specific for each sonar that it must be simulated separately for each trainer. The calculation part for a “ship” roughly consists of the following parts:

1. An inertial simulation for change of speed. In this part, the desired speed as set on the ship’s telegraph is converted into an actual speed.
2. An inertial simulation for course change (the speed at which a ship changes course is highly dependent on desired and actual speed).
3. Splitting the actual speed into a N – S and an E – W component.
4. Integrating the shipping components whereby the relative simulator positions are converted into positions in the fixed sea area.
5. The bearing and distance: The relative positions of each ship are calculated here in bearing and distance. This is for the benefit of the sonar generators and the instructor.

 

 

Coupling of the simulators

From an accuracy point of view, the best interface between these types of trainers is one that transmits ship positions in N – S and E – W components. However, the techniques used by the various trainers present are quite different, while the size of the sea areas also varies widely.

• AN/UQS trainer (Sangamo): The decomposed positions in a synchro value of 200 yards, 60 Hz per revolution, a fixed sea area that is infinite in size.
• Ned. I and II trainers (van der Heem): The decomposed positions analogue 40 0Hz, a fixed sea area of 16 x 16 0f 32 x 32 km.
• Torpedo fire control (HSA): The decomposed positions are digital, 100 kHz, and a navigating sea area of 64x 64 kyards.
• Sonar simulator for a frigate and submarine trainer (LEOK): the decomposed positions analogue DC, fixed sea area of 40 x 40 miles.

Because we are dealing here with existing equipment that may be changed as little as possible, it has been stated that the four surface ships, the submarine and the helicopter in coupled condition will be integrated once into the LEOK trainers with a sea area of 40 x 40 miles. If required, the coupling could be used in 400 Hz analogue or 60 Hz synchro values. This only required a small change in the existing trainers.

The smaller sea areas could be placed anywhere in the large area as desired. An exception has been made for the torpedo. This is accurately simulated and controlled in the HSA fire control system. The relative digital values are therefore converted into analogue DC values according to the LEOK scale in the fixed sea area.

To generate the sonar sounds correctly, including the Doppler shift, and for the benefit of the instructors, the courses and speeds are also linked. However, the links are not arbitrary. There is only one training schedule in which all trainers participate.

 

 

TORPAT

For the visual observation of the four surface ships through the periscope of the simulated submarine, the “Verificatie van RijksZee– en Luchtvaartinstrumenten” (Verification of Governmental Sea and Aviation Instruments) company at Wassenaar, built a projection set-up with a large vertical screen. This screen was arranged over 360 degrees around the periscope with a radius of 3 metres. Special film projectors are located both below and above the upper glass of the periscope. The centre of each projected image is precisely at periscope height (horizon). Each projector can rotate continuously using servo controls and independently of the other projectors. The direction in which each target projector will face is determined by the submarine trainer’s calculator.

 

The film consists of 360 pictures, each picture has a different angle of view. The beginning and end of the film are connected. Using sprocket wheels, it is possible to rotate this film in a servo-controlled left or right direction. If the same image is exposed for a longer period, cooling should prevent the film from deforming. The viewing angle is determined by the calculator of the submarine trainer (OZB trainer). The distance effect is brought in with a zoom lens. This distance ranges from 500 to 10,000 yards. This lens is rotated by a servo motor according to a certain function from the OZB calculator. The target distance can be measured with the periscope. However, the light intensity must remain constant. The lamp voltage is therefore regulated with a servo-controlled Variac according to a special function. If two targets pass each other, the light intensity of the trailing ship will decrease to zero. The horizon with sky and water is obtained from a slide projector that rotates on the periscope. The projection of this is larger than the field of view of the periscope.

The helicopter

One of the simulated frigates has a weapon-carrying helicopter that is also equipped with sonar. This helicopter can be guided by radio to above the target via an artificially generated radar image seen from the frigate. This radar image is generated in the LEOK frigate simulator and also shows the position of the main body, the submarine chaser and the other frigate. Some noise in the background ensures an image that approaches reality reasonably well.

The Exercise Summary Plot (OOP)

The projection screen was formed by a vertically arranged glass plate of 3×3 metres that was matted on the back. Seven symbols of +/- 2 cm were projected onto this. The centre represents the position of that ship in a fixed sea area. From time to time the position of each symbol is marked with a special marker. The resulting rows of points are connected to form a plot of all ship movements. They represent two frigates, a submarine chaser, a main body, a submarine, a torpedo and one helicopter. In addition, a movable rose and a fixed grid were projected. Each symbol has an arrow so that the price is also visible. The grid was displayed with an ordinary slide projector. The eight movable projectors each consisted of a vertical and fixed projector with a movable mirror above it at an average angle of 45 degrees. This mirror could be rotated horizontally and vertically using servo motors. The projection distance was 5.50 metres and the maximum error was 5 mm. The size of the sea area was normally 40 x 40 miles, but any portion of this could be spread over the entire screen to the size of 10 x 10 miles.

Other projects

Both van der Heem trainers and the Sangamo trainer were also equipped with a projector unit with a vertical plot screen. They gave as much information as possible about the convoy. The two van der Heem projectors also showed where the target was supposed to be located via the sonar and whether the target had been hit with anti-submarine weapons.
Only the frigate simulator had a situational overview on a large screen. The sonar measurements were also visible on that simulator. The situational overview screens were only visible to the instructor.

The construction of the integrated training facility

The arrangement of equipment was devised by the anti-submarine warfare school itself. Broadly speaking, the technical design of the interconnections was made by LEOK. The necessary changes to the Sangamo and the van der Heem trainers have been prepared and implemented by the Marine Electronics Company (MEB) in Oegstgeest. The frigate simulator, the submarine trainer with Chief Instructor Panel, Exercise Overview Plot and various modification equipment are designed and built at LEOK.
The periscope unit with its projectors was designed and built by the ‘Verification of National Sea and Aviation Instruments’ organisation in Wassenaar.
The cabling between the simulators was designed by MEB and installed by an installation company.
The equipment was commissioned and adjusted by the MEB and LEOK with the cooperation of the maintenance team of the “Zeearend”.

Source

J. W. Stroethoff, LEOK, Oegstgeest in ROERING, December 1973 (2), p 83
 
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