by Orr Kelly
Although at the time of the attack at Alexandria the British were not in the lead, they were already strong contestants in the race. They were developing their own manned torpedoes, called Chariots, and training teams of torpedo riders, equipped with breathing devices based on Lambertsen’s invention. In October 1942, they made their first combat swim against a most formidable target, the German battleship Tirpitz, then hidden in the inner harbor of Trondheim, far up the Trondheimfjord from the Sea of Norway.
The powerful Tirpitz was a threat to all Allied shipping in the Sea of Norway and perhaps out into the Atlantic as well. In January 1942, Churchill ordered his forces to sink the ship, warning that “the whole strategy of the war turns at this point on this ship.”
The plan called for two Chariots to be loaded aboard a merchant ship, disguised as one of the small freighters carrying peat from the offshore islands to the Norwegian communities up the fjord. Using false papers this ship, the Arthur, would thread its way up the fjord until it was close to the anchorage of the Tirpitz. Then the two men assigned as crew of each of the Chariots would dress in their cumbersome diving gear and climb aboard their torpedo craft. Moving underwater, they would approach the battleship and place their explosive warheads under its keel.
To get through the German patrols, the crew of the Arthur lowered the two Chariots over the side and towed them beneath the water. And then, just as they were in sight of Trondheim and trying to pick out the outline of the battleship, they hit a large wave, and their propeller cut the tow lines. When a diver went down to see what had happened, he found both lines dangling loose in the water. Their mission thwarted, the men scuttled the Arthur, rowed ashore, and made their way overland to Sweden.
The first attempt to sink the Tirpitz ended in failure on 31 October 1942. But the British didn’t give up.
Three months later, in January 1943, eight two-man Chariots were dispatched for an attack on the ships of the Italian navy berthed in the harbor of Palermo, Sicily. The raid was a spectacular success. The Chariot riders sank a cruiser, three submarine chasers, and two merchant ships.
While the Chariots had proved their worth, the British were also busy developing a much more sophisticated undersea craft, a true minisubmarine called the X-craft. The goal was still the same: sink the Tirpitz.
In September 1943, six submarines set off from the secret British naval base at Loch Cairnbawn, in the far north of Scotland. Each had an X-craft in tow. And strapped to each X-craft were two large containers, each containing two tons of explosives. For ten days the subs made their way northward across the rough North Atlantic. This time the Tirpitz and two other German warships were anchored in a fjord near the North Cape of Norway, far above the Arctic Circle. On several occasions, tow lines parted and had to be replaced. One of the minisubs was lost at sea on the crossing. Another began leaking and was forced to abandon its explosive charges. The skipper of the parent submarine decided to scuttle the ailing X-craft rather than try to tow it back to Scotland.
Thus, four X-craft survived the ten-day crossing, having traveled more than a thousand miles, most of the time submerged. With fresh crews, who had made the voyage in the relative comfort of the parent submarines, the four craft set off by themselves at about 6:45 on the evening of 20 September. In these far northern latitudes, they would have only a few hours of darkness, with dawn at about 2:00 A.M. Their major target was the Tirpitz, but two other powerful German ships, the Scharnhorst and the Lutzow, were also docked nearby. With luck, the sixteen men manning the four X-craft would have the chance to strike a crippling blow at the German navy.
Two of the craft wriggled through mine fields and antisubmarine nets and actually bumped against the gray hull of the Tirpitz as they jettisoned their explosive charges, set to go off in one hour. One of the minisubs, disabled by the collision with the battleship, surfaced, and her crew surrendered. Another X-craft almost got away, but was disabled by machine-gun fire and sank. Two of her crew survived and were captured.
When the explosives laid by the two X-craft went off, the Tirpitz had moved slightly. She was seriously damaged, but not sunk. One of the other X-craft entered the harbor but was unable to plant its mines. Another became disabled and was not able to participate in the attack.
The Tirpitz never again put to sea on an offensive sweep and was finally put out of action when it was hit by fourteen bombs in a mass attack by four-engined bombers on 3 April 1944.
By the end of the war the British had an array of underwater attackers, including the Chariots, the X-craft, and the swimmers themselves. Hitler became so furious with the depredations of the swimmers and other commandos that he issued a secret order that all captured commandos, including those in uniform, were to be “slaughtered to the last man.” The X-craft crew members captured in the attack on the Tirpitz were fortunate. Officers aboard the German ship, impressed by their bravery, offered them hot coffee, schnapps, and hammocks. They spent the rest of the war in a prison camp.
In the Far East, the Japanese had developed a small fleet of quite sophisticated little submarines. They were seventy-eight feet long and six feet wide, carried a crew of two, and were powered by diesel engines capable of a top speed of nineteen knots. Five of the subs were carried across the Pacific, each lashed to the deck of a mother submarine, to take part in the attack on Pearl Harbor. But even though several of the little subs, each carrying two torpedoes, managed to get inside the harbor, they inflicted no damage during the attack.
The U.S. Navy took little or no interest in this form of warfare during World War II, even though officers were familiar with the British and Italian efforts and knew of the Japanese minisubs. But in the period of intense experimentation and innovation that followed the war, members of the UDT forces obtained two-man torpedoes from the Italians and X-craft from the British. They were especially interested in the X-craft because, being a true minisubmarine, it provided a good deal of protection for the crew members from the cold and darkness of the sea.
American frogmen became adept at “flying” the X-craft and looked forward to developing a fleet of minisubs of their own. They even managed to develop such a craft.
But navy politics intervened. The submarine force, a much larger and more powerful part of the service bureaucracy, was willing to permit the UDT and its parent, the amphibious force, to operate free-flooding submersibles in which the occupants were surrounded by water. But the submariners insisted that any true submarine belonged to them. The little sub that the UDT men had developed disappeared into the clutches of the submariners, and they never saw it again.
The frogmen faced a dilemma. If they chose to use true submersibles, they would be at the mercy of the submarine force. They would have limited control over the type of craft developed, and they could never be sure the little subs would be available when they needed them. If they chose free-flooding boats, they would have control over the design and operations, but they would face all the problems of operating under the sea with only limited protection from the cold.
The decision was that it was better to be cold and independent. The UDT force decided to focus on developing its own wet submersibles rather than rely on the submarine force to provide it with minisubs.
W. T. (“Tom”) Odum, head of the ocean engineering department of the Naval Coastal Systems Center, in Panama City, Florida, has been involved with the development of these little swimmer-propulsion devices since the early 1950s. The first he remembers is a one-man vehicle in which propulsion was provided by the man pedaling a bicyclelike system that turned a small propeller.
Then, in the midfifties, came the Mark 2, built by Aerojet General according to a design from General Electric. From the outside, the Mark 2 looked like a little airplane, with the two-man crew sitting side by side. Inside, it looked very much like a 1956 Ford pickup. Odum says the designers reasoned that the crew members would find the little craft extremely claustrophobic but that they would be more comfortable in familiar surroundings,
so they modeled it after the interior of a popular truck.
The Mark 2 was the navy’s first effort at a sophisticated swimmer delivery vehicle. It was powered by silver zinc batteries, used a gyroscopic compass, and was equipped both with a hovering system and with thrusters that permitted it to maneuver left, right, up, and down.
Unfortunately, it was, as Odum says, “a hydrodynamic nightmare—it just didn’t have any stability.” The little craft never got beyond the experimental stage. It was so unstable that it could not even be towed through the water until it had been pulled up onto a large sheet of plywood.
About the same time, the navy also developed the Mark 1 SPU (swimmer propulsion unit) which was powered by silver zinc batteries and designed to drag the swimmer through the water a little faster than he could swim on his own. He controlled the speed with a pistol-grip throttle. The device worked, but the navy decided not to use a one-man vehicle, and the program was killed.
In the midsixties, with the war in Vietnam heating up, work began on the kind of free-flooding SDV now in use in the fleet. Beginning in 1964, the coastal systems center developed the Mark 6 SDV. It was a two-man vehicle, but the front and rear could be separated for the insertion behind the cockpit of a five-foot-long pod that held either electronic equipment or two more swimmers. The Mark 6 was extremely stable and easy to fly, and it was the first SDV with a usable Doppler navigation system.
Next came the Mark 7, a four-man boat modeled after a two-man Italian submersible. The Convair division of General Dynamics built about a dozen of the craft, and the Mark 7 became the first SDV to move beyond the experimental stage and into use by the fleet. The Mark 7 never won any beauty contests. It was an awkward-looking boat, with a square shape, a rounded nose, and a tapered tail. It wasn’t very fast or very maneuverable, but it was stable and very dependable. “Just a work horse,” Odum says. Two of the early model Mark 7s were used—and lost—in Operation Thunderhead.
The Mark 7 proved to the navy that SDVs could be very valuable because of the way in which they increased the range of the combat swimmer and yet permitted him to remain hidden under the water. But it was also obvious from the experience with the Mark 7 that something better was needed.
Work began on the Mark 8, and the navy quickly decided to build the craft itself at China Lake, a naval research facility in the southern California desert that normally focused on the development of missiles. There, far from the sea, the six-man Mark 8 was put together and then taken to a freshwater reservoir for testing. The Mark 8 was bigger than the Mark 7, capable of carrying six men rather than four, and its equipment was much more sophisticated, including sonar and an inertial navigation system. The goal was a craft that could operate for six hours at a speed of six knots.
While work was under way on the Mark 8, the navy decided it also needed a separate two-man boat to do reconnaissance and carry weapons. This became the Mark 9.
In the Mark 8—the SEALs call it the bus—the six SEALs sit upright, with the pilot and navigator in the two front seats and four combat swimmers behind them. In the Mark 9, the two swimmers lie on their bellies, side by side. With two propellers and a flat shape, the Mark 9 is highly maneuverable. Flying the Mark 9, the SEALs say, is fun, like driving a sports car or a fighter plane.
Operating an SDV is not an occupation for anyone with even the slightest tendency toward claustrophobia. Even many SEALs, brave men who don’t flinch at jumping from a high-flying plane or engaging in a firefight, don’t want anything to do with what seems to them like being locked in a little black coffin deep under the water. Men in an SDV have virtually no room to move about; they are surrounded by cold water, and they are in total darkness except for the dim glow from their instrument panel.
With the Mark 8 and the Mark 9, which came into service in the late 1970s, navy special warfare finally had a unique capability for operating clandestinely under the seas over relatively long distances.
By that time, too, many of the tactics for use of the SDVs had been worked out with the earlier Mark 7s. The SEALs learned how to maneuver into a harbor, slide back the canopy, and photograph the bottom of a ship, even at night. They adapted the Mark 37 torpedo and found that the two-man Mark 9 SDV could carry two of them. The SDV’s aiming system was much more primitive than that of a full-scale submarine, but the frogmen found that, lying just below the surface, they could aim accurately enough to hit and disable a ship.
Much of their effort was devoted to mine warfare. With their sonar, they could help to locate mines. And with their ability to move about undetected, they could approach enemy ships and place limpet mines on their hulls. In this procedure, one man causes the SDV to hover while another, linked to the craft by a safety line, swims to the ship and attaches the mine.
One of the key innovators was then–Lt. Comdr. Tom Hawkins, who served as commander of UDT-22, an East Coast team that pioneered the use of SDVs, and later as the first commander of SDV Team Two, when the SEALs and UDT were combined in 1983. Hawkins says they got extremely good at what they did.
He tells about one demonstration attack on a flotilla of destroyers anchored in Chesapeake Bay.
“I went on board and the admiral offered me coffee,” he recalls. “I said, ‘Admiral, you have seven ships anchored here. At the slack tide, we’ll bring an SDV out of that channel over there. These guys are going to come over here and systematically hit that ship, that ship, that ship.… They will put an inert limpet mine on each ship. Within several minutes, a flare will come to the surface.’ This guy gives me the ho, hum.
“I told him, ‘At eight o’clock you’re going to see the first flare go off over there. I would like you to alert all your sonar operators, tell everyone manning the gunnels to be aware, try to catch us.’ Ho, hum. The first flare went off at eight o’clock. All of a sudden he had seven destroyers lying on the bottom. He became concerned. We’re going to go back and write an after-action report on this thing. We’re getting graded, and he’s getting graded.”
Hawkins told the admiral they would be back the next night and told him the order in which the ships would be hit.
“We did the same thing to them again,” he says. “They never knew we were there.”
In another demonstration, swimmers were parachuted into the Intercoastal Waterway near Eglin Air Force Base in Florida, mated up with an SDV that had been positioned there, and maneuvered in toward the air base. They parachuted with what Hawkins will describe only as “a very classified weapon.” Their job was to place it on a dock at Eglin. For many years, UDT and SEAL teams were trained in the handling and use of small nuclear weapons, and it is probably such a device that Hawkins was referring to. The SEALs are no longer trained to use nuclear weapons.
Hawkins waited on the pier for the swimmers to arrive. He was confident he would see them coming. He knew where they were coming from and when. They were using old-style breathing apparatuses that left a trail of bubbles, and Hawkins had a well-trained eye for such telltale signs. But they caught him by surprise when one of the swimmers surfaced and handed the device to a petty officer waiting with Hawkins.
“A lot of times we had trouble selling the SDVs,” Hawkins says. “People said they were just toys. But they cease to be toys when you can do something like that. It was an incredible event. Even I was impressed.”
SDVs can, of course, be detected, but that is very difficult. They are virtually silent, and their plastic shell makes a poor target for detection devices.
“We’ve measured the signature of an SDV,” Hawkins says. “Of course it has a signature. But I used to tell my men they’ll never get you the first time. If you go into a harbor and shoot off one of those torpedoes, how in the name of God are they going to know where it came from? If you do it two times, three times, four times, in the same harbor, they’re going to get you.”
For a number of years, the navy experienced serious problems with the reliability and maintainability of the Mark 8 and 9 SDVs. The skipper of one team
complained that his force was only a paper threat because his craft were laid up for repairs most of the time. But that situation has changed. Lt. Comdr. Doug Lowe worked in SDVs a decade ago and then was ordered back as executive officer of SDV Team Two in the fall of 1990. He was not overjoyed at the assignment.
“In most of our dives, I don’t think we had a 50 percent success rate. We were shitty. When people talked about me coming back to SDVs, that was real frustrating for me,” Lowe says. But, when he joined the team at Little Creek, he was much impressed by the progress that had been made. Reliability, he found, was more like 90 percent than 50 percent.
The Achilles’ heel of the SDV is the problem of mobility—getting it to the war. SDVs can be flown anywhere in the world, but then there is the problem of unloading that strange-looking device at a foreign airfield. Or they can be carried aboard a surface ship and dropped into the sea by a crane. But that has to be done well out of sight of a potentially hostile shore, and there is always the chance that it will be seen. The U.S. Navy has never found enough money to do what the Italians did during World War II: restructure a surface ship so SDVs can be operated through a door below the waterline.
On one occasion, the navy wanted to get a look at a Soviet ship. But the ship was anchored in a Cuban harbor, about eighteen miles upriver from the sea. With fresh batteries, an SDV could probably have made the thirty-six-mile round trip. But it didn’t have the range to carry out the mission if it was launched from a surface ship well outside the territorial waters claimed by Cuba. The mission had to be called off.
SDVs can also be lofted by helicopter. One of the early experiments in transporting an SDV in this manner turned out disastrously.