Cutaway view of a Tomahawk land attack conventional (TLAM-C) cruise missile.
Note the 1,000-lb high-explosive warhead. JACK RYAN ENTERPRISES, LTD.
A Tomahawk cruise missile is launched from the USS La Jolla (SSN-701) on the Pacific Missile Test Center (PMTC) range. OFFICIAL U.S. NAVY PHOTO BY GERRY WINEY
The basic nuclear land attack version of Tomahawk, known as B/UGM-109A (also called TLAM-N), is launched into the air by a small rocket booster. Once airborne, a miniature jet engine about the size of a basketball ignites to power the missile at about 500 knots. It flies low to the surface (whether over the open ocean or land), held there by a guidance unit (MGU) being fed by a radar altimeter. The missile is kept on course by the MGU utilizing an inexpensive strapdown inertial guidance system. Once over dry land, the MGU is updated with position data from a system known as Terrain Contour Matching (Tercom), which matches the terrain under the missile with a three-dimensional database in the memory of the MGU. By using periodic Tercom updates, a TLAM-N is normally able to place its 200-kiloton W-80 nuclear warhead between the uprights of a football goal-post after a 1,300-mile flight.
While the nuclear-armed version of Tomahawk was being developed, it occurred to a number of people that perhaps the Tomahawk could be used to carry other things, and thus was born the whole family of conventionally armed Tomahawks in service now. The first of these was the B/UGM-109B Tomahawk Anti-Ship Missile (TASM), which replaced the TLAM-N MGU with a modified radar seeker and MGU from the A/R/UGM-84 Harpoon antiship missile. In addition, the W-80 nuclear warhead was replaced with a 1,000-lb/455-kg high-explosive warhead.
The idea was to provide units of the U.S. Navy with a really long-range (250 NM/410 km) antiship missile. One problem that had to be overcome was the fact that a TASM flying out to hit a target ship at maximum range would have to fly almost thirty minutes to get to the target area. During this time, a fast warship might travel as far as fifteen to twenty miles, so a special series of search patterns was added to the TASM launch and control software. These search patterns comprise a series of “expanding boxes” designed to allow the TASM to fully search the uncertainty zone or the possible target area. In addition, TASM has a passive ESM system called PI/DF (Passive Identification /Passive Direction Finding), which is designed to direct TASM onto larger enemy warships, probably through detection of their large air-search radars.
Following the TASM into service was the largest subfamily of the R/BGM-109 program, the Tomahawk Land Attack Missile-Conventional (TLAM-C) series. This particular series takes the basic guidance system of the TLAM-N, adds the high-explosive warhead of the TASM, and a new terminal guidance system called Digital Scene Matching (DSMAC). It has a range of roughly 700 NM/1,150 km, and uses the same basic Tercom system to get into the vicinity of the target. DSMAC is an electro-optical system that matches the image from a small television camera in the nose of the TLAM-C to one stored in system memory. This system can even be used at night, with a strobe light on the target during the final approach. Called the B/UGM-109C, it became the first of the Tomahawk series to be used in combat, during Operation Desert Storm.
Several derivatives of the basic TLAM-C include the B/UGM- 109D, which replaced the basic high-explosive warhead with a dispenser for 166 BLU-97/B combined effects (fragmentation and blast) submunitions. Called TLAM-D, these Tomahawks are particularly effective against vehicles, personnel, soft targets, and exposed aircraft. A further variant of the TLAM-D, which is armed with antirunway cratering submunitions, is known as the B/UGM-109F. The newest version of Tomahawk, called Block III, incorporates a number of new features such as its own Navstar GPS receiver, a new penetration warhead, an improved engine, and more fuel to bring its range to over 1,000 NM/1,640 km. It should be operational in 1994.
All the various types of Tomahawks can be loaded and fired from any 21-inch/533mm torpedo tube or VLS tube on the Miami. Besides twelve missiles in the VLS tubes, additional Tomahawk rounds, as required by a particular mission, can be stored in the torpedo room. This makes Tomahawk the most flexible strike system ever deployed by the U.S. Navy. It also opens a new dimension for the U.S. SSN force, since now they can join the surface and air forces in striking “over the beach” at significant targets.
The following might be a typical mission load-out for the Miami. When preparing to leave for a cruise to the Mediterranean, she might carry a full load of Tomahawks, which would include twelve VLS tubes full of TLAM-C/D variants, with several more in the torpedo room racks. In addition, she would carry a mixed load of Mk 48 Mod 4s and ADCAPs, as well as several Harpoon Block ID antiship missiles. There would be no TLAM-Ns, as all of these have been withdrawn from U.S. ships, aircraft, and submarines following President Bush’s order in the fall of 1991. Nevertheless, though it is the policy of the U.S. Navy not to deploy nuclear weapons, and they normally refuse to discuss it, the capability does still exist. Also, there would be no TASMs aboard, as the submarine community seems to feel that the Harpoon Block ID is more than adequate to the antishipping task, and the TASMs are hard to get long-range targeting for, on a submarine.
The biggest single bottleneck to effectively utilizing the growing force of TLAM-C/D cruise missiles in the inventory is the preparation of suitable mission plans. Each mission plan has to be developed from a Tercom data base that the Defense Mapping Agency (DMA) has assembled over a period of fifteen years. The data is made into mission plans at one of the Theater Mission Planning Centers (TMPC) located at various places around the world. Here the Tercom data bases are merged with terminal target photos (for the DSMAC cameras), to produce mission plans that can be stored on disk packs on the sub, or downloaded to the sub via a satellite link.
Once the Miami has a particular mission plan aboard, the basic plan can be modified on the BSY-1 Command and Control System (CCS Tac Mk 2) console in the control room. Located adjacent to the BSY-1 fire control consoles, this console can be used to plan and control missions for all the variants of Harpoon and Tomahawk. Should Miami not have a plan available in her onboard library, she can use the CCS-2 to develop her own plans. And with the coming deployment of the Block III version of TLAM-C, the requirement for access to a complete Tercom library for mission planning will be reduced.
To launch a Tomahawk or Harpoon, the boat has to slow to about 3 to 5 knots and come to periscope depth. The CCS-2 (or BSY-1 in the case of Harpoon or TASM) console operator powers up and loads a mission plan into a missile loaded in either a torpedo or VLS launch tube. This can be done for as many or as few missiles as the situation requires. Once this is done, the weapons officer inserts a launch key (a holdover from the old TLAM-N days) and presses the firing button. If the weapon is a Tomahawk, it is ejected from the tube (the version fired from torpedo tubes is carried in a tube liner), fires its booster rocket, and away it goes. If it is a Harpoon, the weapon in its buoyant capsule is ejected from the tube and heads for the surface. When it gets there, the booster rocket fires, and it heads for the designated target.
The one problem with all these missiles is that they make the firing submarine extremely vulnerable to detection by aircraft or surface ships, and the amount of noise made by a missile being fired underwater is simply amazing. So it is essential that if the Miami is ever tasked with firing a weapon, as the USS Pittsburgh (SSN-720) and USS Louisville (SSN-724) did during Desert Storm (they fired a total of fourteen TLAM-Cs and TLAM-Ds), she will have to be sure she is clear of any threat during the launch cycle.
Mines
Probably the least appreciated weapons that can be carried by a 688I are mines. These “weapons that wait” are perhaps the most cost effective weapons ever derived for naval warfare. Though most of the mining done by the United States since the end of World War II has been done by aircraft, there may be situations where the stealth and precision of a submarine may be preferred for delivery of these dangerous “eggs.”
The first of these is the Mark (Mk) 57 moored mine. It is a derivative of the air
-dropped Mk 56 and can be moored in several hundred feet of water. It has a variety of different sensor and triggering systems, including acoustic and magnetic influence fuses. They can be programmed for activation delay or programmed to activate only for certain types and numbers of ships.
Another type is the Mk 67 mobile mine. These are obsolete Mk 37 torpedoes that have been rebuilt into mines that lie on the bottom and wait for a target to drive over them. A submarine might fire them up into a shallow channel, to a distance of 5 to 7 miles. Like the Mk 57, this mine has a variety of different fusing options.
Mark 57 moored mine. JACK RYAN ENTERPRISES, LTD.
Mark 67 submarine-launched mobile mine (SLMM). This is a converted Mk 37 torpedo designed to be fired from a distance, then to sink to the ocean floor to act as a bottom mine. JACK RYAN ENTERPRISES, LTD.
Mark 60 Captor mine. The long capsule contains sensors and a Mark 46 ASW torpedo. JACK RYAN ENTERPRISES, LTD.
But the crown jewel of the U.S. mine arsenal has to be the Mk 60 Captor mine. This is an encapsulated Mark 46 torpedo, programmed to wait for enemy submarines; when one is detected the torpedo swims clear and attacks the sub. As an added benefit they can be programmed to listen for a certain type of submarine, like a Kilo or Akula. During the Cold War, it was planned to seed Captors along all the transit routes used by the submarines of the Soviet Union. Now they can be used against any of the growing number of countries that have chosen to buy and use diesel submarines in their navies.
One of the nice things about mines is that they take up only about half as much space as the other types of weapons a sub might carry. Thus a 688I could carry as many as forty mines and still have a couple of ADCAPs for self-protection. The deployment of the mines is no different from loading and firing a torpedo (the BSY-1 has a mine launch mode), though the position of the mine has to be plotted absolutely accurately, so that it can be swept later. Fortunately the advent of GPS has made this task a bit easier, though efficient use of the SINS system is also required.
Forward escape trunk of USS Miami. Note the air bubble where the crew/swimmers would stand before egressing from the trunk. JACK RYAN ENTERPRISES, LTD.
All in all, these weapons make for a very dangerous quiver of arrows for the submarine force.
Escape Trunks/Swimmer Delivery
Wandering aft about 25 feet from the enlisted mess puts you underneath the forward escape trunk. This is a two-man air-lock used for a variety of purposes, though primarily as the main entry point to the forward part of the boat. It is composed of a pressure vessel about 8 feet tall and 5 feet in diameter. At both the top and bottom is a hatch capable of standing as much pressure as the actual hull of the boat. Most often personnel and supplies are loaded through this trunk. There is also another trunk farther back over the aft machinery spaces.
In the event of an emergency the escape trunk comes into its own. If the boat is on the bottom and stable, the normal procedure is to wait for one of the deep-submergence rescue vehicles (DSRV) to be transported to the rescue site. The DSRV then comes down and docks to the collar over one of the escape trunks. It blows out the water from its own docking collar, now held in place by the pressure of the surrounding water. The crew of the DSRV open their own bottom hatch and enter the downed boat through the trunk. Now the crew of the downed sub can come aboard, albeit only about two dozen at a time. This means that if a Los Angeles boat were to go down intact with all her crew alive, it would take something like six trips to get them all off.
If the boat is flooding and the crew must get off immediately, the escape trunk takes on a more vital role, allowing the crew to escape from the boat under their own power. This is done using a Steinke hood, a combination life jacket and breathing apparatus that fits over the head of a sailor. Two at a time the men enter the escape trunk wearing their Steinke hoods. They close the bottom hatch and huddle under an air bubble flange installed in the trunk for such operations. The sailors then charge their Steinke hood air reservoirs from an air port in the side of the trunk, and open a flood valve to fill the trunk with water. While they sit under the air bubble flange, the upper hatch opens. If they are the first ones to escape from the sub, they will have the additional job of pushing a life raft out of the hatch; this floats to the surface and provides some shelter for the men when they get there. Then, one at a time, they duck under the flange and float up through the hatch.
A student dons a Steinke Hood to practice escape from a sunken submarine. JOHN D. GRESHAM
At 400 feet (the maximum depth that the hood can be used), the men will have something like a minute to flood the trunk and get out. Any longer, and they risk getting “the bends” (small bubbles of nitrogen gas that form in the blood) as they rise to the surface. After they have exited, the controller in the area below the trunk closes the hatch via his control panel and begins to drain the trunk for the next pair of escapees. Meanwhile the two sailors literally rocket up to the surface. This would be extremely dangerous (the decreasing water pressure makes them vulnerable to a variety of air embolisms if they hold their breath), but with their heads in the air bubbles of their Steinke hoods, the men are able to breathe normally throughout the ascent to the surface. Once on the surface, they try to inflate the raft and stay together.
A diver prepares for egress in one of Miami’s two escape trunks. JOHN D. GRESHAM
One of the other primary uses for the escape trunk, this one far less ominous, is as an airlock for divers and special operations teams. One of the little-known facts about U.S. submarines is that they have, at all times, a small team of divers (usually three to five rated divers) aboard to support the operations of the sub. The diving equipment and other gear is stored in the compartment forward of the torpedo room, near the VLS support equipment room. The divers’ jobs include everything from clearing fouled propellers and running gear, to running security checks on the boat before she leaves harbor. In fact, when the Miami is in a foreign port she is not allowed to leave the harbor unless she has at least three divers aboard to assist in examining the hull before she gets underway.
The other type of diver-related operation that is conducted through the escape trunk is submerged “lock-out” of special operations teams, such as the U.S. Navy’s elite SEAL teams. These kinds of operations are really not the forté of the 688I and will, until they are retired, be predominately the job of modified Sturgeon-class boats like the Parche (SSN-683). Part of the problem is that the Los Angeles-class boats are optimized for speed and are not properly equipped to conduct this kind of mission effectively. Also, the already cramped accommodations of the 688I make it necessary to set up temporary sleeping quarters for the team, perhaps on bunks down in the torpedo room.
In the unusual case of a special operations mission, the boat nears the target of the team and hovers over the seabed. The team then enter the trunk two at a time under the air bubble flange, and follow the same procedure as escaping sailors except with their diving gear. Retrieval is exactly the reverse, with the team reentering the trunk two at a time, closing the hatch, draining the trunk, and exiting through the bottom hatch back into the boat.
The Sounds of Silence—Acoustic Isolation
Silence. That is what has made American boats better than their opponents for over thirty years. It is their armor and their cloak all wrapped up into one vital quality. Nevertheless it comes at a high price and is called a fragile technology—fragile because it is based upon well-understood principles of physics, and because it can be compromised so easily. In terms of military technology, it is one of the crown jewels, in the same category as the ability to build stealth aircraft and nuclear weapons. So effective has this silencing effort been that the latest U.S. SSNs and SSBNs are so quiet, they can effectively disappear in the ocean’s background noise.
To make a quiet submarine, the naval architects must take a holistic attitude to the design of the boat and every piece of equipment that goes into it. The key is mounting each piece of equipment that m
oves or makes noise on something that damps out the vibrations. The transmission of these vibrations—things like the spinning of a pump or the hum of a generator—sends noise out into the hull, where it is radiated into the water. In addition, the rubber decoupling tiles coating the hull help keep noise inside the hull from being transmitted out into the water.
The mounts on the main machinery raft take care of the biggest source of radiated noise. The rest of it is probably taken care of by secondary mounts underneath each piece of equipment (pumps, turbines, etc.), designed to attenuate the specific type of noise generated by that particular piece of equipment. In addition, each piece of machinery is probably designed to be as smooth running and noiseless as America’s best mechanical and electrical engineers can make it. For example, the seawater circulation pumps, which are arguably the most noisy devices on the boat, transmit almost no noise in the 688I-class boats. Supporting this is a noise-monitoring system with sensors throughout the boat designed to tell if any piece of equipment or gear is loose or malfunctioning. An added benefit of this system is that it probably is capable of predicting when and how a piece of machinery is going to fail by its acoustic signature (such as the sound of bearings wearing out).
The various techniques used to decrease the radiated noise of American submarines constitute the single most classified aspect of the Miami and her sisters. The above description is only the most cursory discussion possible of this incredible technology. In fact, the only real way to describe the magnitude of the achievement is to say that the S6G reactor generates something like 35,000 shaft horsepower10, yet with all this power the total noise radiated by the Miami is probably something less than the energy given off by a 20-watt lightbulb. It is for this reason that submariners sometimes refer to their Air Force cousins flying the F-117A stealth fighter as “the junior stealth service.”