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The Navy’s combat swimmer differs from most other combatants in that he operates alone or nearly alone in a hostile oceanic environment. He carries a tremendous responsibility toward the success of every amphibious landing, because the intelligence he collects bears heavily on the task force commander’s decision of where and when to land the landing force.
The combat swimmers are members of commissioned units—Underwater Demolition Teams. Four teams are now in commission, each with an allowance of 15 officers and 101 enlisted men under a lieutenant commander. The teams are divided into two-officer, 20-enlisted-man platoons, trained and equipped to function either separately or together in a team operation. Team members come from a variety of ratings, there being no restrictions in this regard. Every qualified combat swimmer is the product of intensive training—having completed four months of basic UDT school, six weeks of underwater swimmer training, and, usually, three weeks of parachute jump school. Constant operational training and frequent requalification in specific skills keep each man in a state of readiness. Officers and enlisted personnel go through the same training and share the same dangers in combat. Underwater Demolition Teams are somewhat misnomered, for their foremost task is that of intelligence collection— gathering information concerning sea approaches to landing beaches, the beaches themselves, and nearby areas. They become demolition teams when these beaches must be cleared of obstacles, or when specific coastal targets of military importance are singled out for destruction.
In a typical operation as part of an amphibious task force, a UDT platoon is transported to its objective area by a parent ship, normally an LSD or a converted destroyer escort such as the Earle B. Hall (APD-107) above. Prior to D-Day—anywhere from three or four days to a few hours before—the UDT men embark in their LCPLs, and make last-minute checks of the equipment necessary for their reconnaissance mission. Neoprene foam rubber “wet" suits are standard gear in all cold water operations, as well as on long missions in warm waters.
Air bubbles in the foam rubber and a layer of water trapped between body and suit slow the escape of body heat, greatly lengthening the swimmer’s endurance. Foam rubber gloves, face mask, swim fins, knife, and life jacket extend his capabilities and provide a margin of safety. Operations at night, in strange and often deep waters, provide the combat swimmer with no means of reference to the outside world, and his wrist compass, watch, and depth gauge are vital both to his survival and the success of his mission.
Hydrographic Reconnaissance may be carried out in daylight or under the cover of darkness. Reconnaissance at night, while more difficult, substantially reduces the chance of discovery by the enemy. Combat swimmers normally do not carry any weapons other than a knife, relying rather on concealment and surprise for protection. In a typical reconnaissance mission, the LCPLs each make a high speed sweep parallel to the beach, casting swimmers from an inflatable rubber boat lashed to the seaward side of the craft. The swimmers go into the water in line and at intervals of about 25 yards. Offshore reefs, the need for covertness, or gunfire harassment from the beach may require that they debark as much as one mile offshore. Once in the assault area, the swimmers commence a co-ordinated survey of the waters and underlying bottom. Each man carries a plastic slate and pencil on a neck cord, and makes note of obstacles, bottom conditions, and every other feature that might affect the successful beaching of landing craft. With a lead line the swimmer takes a sounding every 25 yards, from the 3\-fathom curve to the beach. Upon completion of the reconnaissance and the recovery of swimmers, the swimmers’ information is compiled into a beach sketch and sent to the amphibious task force commander.
Demolition may be required for the removal of obstacles or natural barriers that have been located during the reconnaissance phase. The combat demolition pack is the basic tool in obstacle clearance, having been developed to complement UDT’s unique underwater capability. The 20-pound pack consists of ten blocks of high explosive, detonating cord, a canvas container, and sash cord for securing the pack to an obstacle. Each two-pound block may be employed separately, or the entire pack detonated as a unit. As the packs can be made buoyant by a floatation bladder, a swimmer can tow as much as 100 pounds of explosives. The bangalore torpedo, at right, consisting of a long metal tube containing explosives, is useful in clearing lanes through antipersonnel minefields and barbed-wire entanglements. “Explosive” hose, packed with flexible explosive, may be coupled end-to-end to whatever length desired and used to clear a channel through a reef or a shallow area. Several hours prior to H-hour, the combat swimmers “load” the obstacles and link them together with detonating cord. The demolition field explodes as the recovered swimmers proceed back to sea in their LCPLs.
Swimmer Recovery is a critical phase of every UDT operation. The snare recovery method, developed during World War II, is still the primary means used today. As the pickup craft proceeds at top speed along a line of swimmers, a “snare” man in the inflatable boat alongside places the rubber loop over the outstretched arm of each swimmer in turn. Assisted by the elastic bungee connecting the snare to the boat, the “snare" man swiftly pulls the swimmers aboard. A more recent development is the Fulton sea sled recovery, seen here in use during UDT training operations in the Virgin Islands. This recovery technique requires two passes by the pickup craft, the first to drop off two fiberglass sleds connected by a synthetic line. As many as 10 swimmers may then enter each sled over its open stern. As the recovery craft sweeps between the sleds, a probe on its bow engages the line, guides it into a winch, and the sleds are reeled in, the swimmers then boarding the craft via a trailing canvas mat. The sea sled method has an advantage in that it may be used for recovery at night, an operation difficult or impossible with the snare method.
Aerial Delivery and Recovery allow for rapid UDT reaction when required by an urgent tactical situation. Most combat swimmers are qualified parachutists, and may be dropped into the combat area by either helicopters or fixed-wing aircraft. Low level casting, seen at left below, of swimmers from a helicopter may also be used, dropping the men without parachutes from an altitude of 20 feet at a speed of 20 knots. Pickup is accomplished by trailing a ladder from the helicopter in the water. As the helicopter passes overhead at 20 knots, the swimmer grasps the ladder and swings himself around and up into the aircraft. Perhaps the most spectacular development in recovery systems is the Fulton “Skyhook” fixed-wing aerial recovery system. Permitting the direct pickup of a man from land or water, this procedure involves air-dropping a fOO-pound kit, containing harness, nylon pickup line, tanks of compressed helium, and a deflated balloon to the swimmer. He dons the harness and inflates the balloon, which then holds the 500-foot recovery line aloft. A fixed-wing aircraft equipped with a V-shaped probe engages the line, lifting the man into the air, and he is winched into the aircraft. As many as four men may be recovered simultaneously on one pickup line with this system.
Subsurface Delivery is employed when maximum secrecy is required. The submarine is an effective delivery vehicle, permitting swimmers to lock out and later return and lock while remaining completely submerged. Seven-man inflatable rubber boats with silent running motors may be cut loose from the submarine’s deck and inflated to provide exceptionally silent entry into an area. Midget submarines such as the X-l, above, while limited in range and carrying capacity, can transport small numbers of combat swimmers into shallow or restricted waters which are denied to larger submarines.
Support Systems, including the three types of SCUBA seen in use, at right, to enable the combat swimmer to carry out better his many and varied tasks. The completely-closed-circuit oxygen rebreathing unit (bottom) leaves no bubble trail, and is used on swims where covertness is of the utmost importance. The danger of oxygen poisoning prevents its use at depths of over 25 feet, however. The semi-closed, mixed gas, oxygen-nitrogen rebreather (center) leaves very few tell-tale bubbles and is used on swims of very long duration and at great depths. The open circuit air breathing SCUBA (top) is rendered useless in combat situations due to its bubble trail, but because of its advantage of simplicity, it is often used in non-combat operations. Battery-operated underwater swimmer phones may be integrated into all three types of SCUBA for underwater voice communications. The AN/PQS-lB hand held sonar, at right below, can locate submerged obstacles and objects at ranges of up to 120 yards, as well as being a passive listening device. For short-range transportation, the Mark I swimmer delivery vehicle (SDV) above at left, can tow one or two swimmers at speeds of three or four knots. Electrically-driven four-man SDVs, can silently transport swimmers, equipment, and explosives over ranges of up to 60 miles.
The Underwater Demolition Team, -perhaps more than any other unit in the Navy, relies on the teamwork and personal capabilities of each of its members. Although the combat swimmer uses a myriad of equipment, simple and complex, to broaden and extend those capabilities, it is the strength of his will to succeed and the extent of his training that determine the ultimate limit of what he can do.