Underwater Navigation

13. Combat divers may have to approach a task site underwater to minimize detection and observation from the enemy. They must be highly proficient at the skills and techniques required to navigate underwater. The lack of visible features, currents, tides, and waves are factors that affect underwater navigation. There are no visible references when navigating underwater, and frequent ascents to the surface increase the chance of detection and increases air consumption. Combat divers use a combination of time and kick cycles to measure the distance they have covered under water.

14. Combat divers must know the length of time and number of kick cycles it requires for them to cover a fixed distance, generally 100 m, with various loads, diving ensembles, and water conditions. This component of underwater navigation varies greatly between individuals and must be practised and exercised, regularly and often, to maintain. With the use of an attack board, knowing the time required and number of kick cycles to cover a set distance, combat divers can navigate underwater free swimming, as pairs or as part of a group, to approach an objective. The components of an attack board are:

a. compass—with a luminous face or back lighting;

b. chronograph—a digital timer, used to monitor time travelled; and c. depth gauge—to maintain a consistent, planned depth.

15. A detailed study of maps and marine charts and knowledge of currents and tides are essential when planning a task involving underwater navigation. Once the current and tide information is calculated, an approach plan is developed with distances, any turning or way points, and times of travel. Increasing the number of way points and the distance, increases the possibility of error unless there are prominent landmarks, water reference points, or planned surface checks. With the navigational plan completed, the divers will follow the basic procedures for a submerged navigation swim:

a. Ensure operability of artificial light sources on the compass board or its components.

b. Preset bearings and, if possible, times, distances, and maximum planned depth; upon entering the water, link up with the diver's partner, confirm and set bearing.

c. Descend to planned depth and immediately commence swim. The use of the buddy line will ensure pairs remain in contact. The diver who is not navigating will prevent possible collision with any obstacles.

d. Confirm location along the route if necessary. The navigator will break the surface with minimum exposure and confirm the bearing; the partner can assist in descending by remaining submerged at the extent of the buddy line, then pulling the navigator down. The team then descends to the planned depth and continues.

e. Upon reaching the objective, if a transition to land is required, the procedure detailed earlier will then be conducted.

16. Group Navigation Control System (GNCS). Some combat diving tasks require divers to approach an objective as a team. A GNCS may be used to achieve this. By adapting the basic concepts of underwater navigation as free-swimming pairs, a team of divers can move as a group. The basic formation consists of pairs of divers in file, with a light buoyant line extending between them. Figure 3-2 illustrates the GNCS. The general procedure for this system is:

a. The lead pair of divers acts as the primary navigator for the group. One diver navigates while the other controls the GNCS line and communicates with trailing pairs with the line.

b. After entering the water, the team links up, establishes the formation, and descends to the planned dive depth.

c. While swimming, all divers are responsible to maintain the planned depth of the dive.

d. A designated diver in each pair maintains control and tension of the line.

e. A second pair may be designated as secondary navigator; this will likely be the last pair in the formation.

f. In the event that a diver has to ascend due to an emergency, the buddy will ascend with him or her. The pair nearest the ascending team will be notified. If a pair ascends, then the team supervisor must regroup the team and reconsider the approach; this may require aborting the dive.

17. The key elements to success and safe implementation of this system are the use of the buddy system, detailed planning, as well as the rehearsal of all procedures and potential contingencies. All team members must be proficient in buoyancy control and have an awareness of the planned details of the dive and navigation.

18. The GNCS line will be a continuous length of buoyant nylon or polypropylene rope. It must be long enough to accommodate the team, prevent members from interfering with each other while swimming, and prevent the fouling of any towed loads. The line should be of suitable diameter to be easily visible, and it should not of the same colour as the buddy-lines. Non-corrosive snap-links, fastex buckles, or clips are spliced or fastened along the line at each pair's position. A snap link or clip is attached to each pair's buddy line, then clipped into the group line at each respective location. Standard or prearranged rope signals will be used to communicate along a GNCS line.

19. Through-water wireless communications should be considered when using a GNCS as they will facilitate control and passage of information; however, use of rope signals can be applied. The use of such communications devices will depend on the threat, the ability of the enemy to monitor our through water communications, and the warning the enemy may have on the use of divers. Generally, an enemy threat will preclude the use of a through-water communications system.

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