by Joe Buff
ESGN: the latest submarine inertial navigation system (see INS below). Replaces the older SINS (Ship’s Inertial Navigation System).
Fathom: a measure of water depth equal to six feet. For instance, one hundred fathoms equals six hundred feet.
Firing solution: exact (or best estimate) information on an enemy target’s location, course, and speed, and depth or altitude if applicable. A good firing solution is needed to preprogram the guidance system of a missile or torpedo so that the weapon won’t miss a moving target.
Floating wire antenna: a long, buoyant antenna wire that is trailed just below the surface by a submerged submarine, for stealth. Such an antenna can receive data at a higher rate (higher baud rate) than ELF radio (see above). Recently, floating-wire-antenna technology has been developed to the point where the wire is able to transmit as well as receive, allowing two-way radio communication while the submarine is completely submerged. (To transmit or receive radio data at a very high baud rate, such as live video imagery of a target, the submarine must come to periscope depth and raise an antenna mast out of the water — which might compromise stealth.)
Frequency agile: a means of avoiding enemy interception and jamming, by very rapidly varying the frequency used by a transmitter and receiver. May apply to radio or to underwater acoustic communications (see gertrude below).
Frequency power spectrum: a display of the relative strength of noise being detected by a sonar array at different sound frequencies. Such data can be valuable in locating and identifying passive sonar contacts, especially when tonals (see below) stand out within the display.
Frigate: a type of oceangoing warship smaller than a destroyer.
Fuel cell: a system for quietly producing electricity, for example to drive a submarine’s main propulsion motors while submerged. Hydrogen and oxygen are combined in a chemical reaction chamber as the “fuels.” The by-products, besides electricity, are water and heat.
Gertrude: underwater telephone. Original systems simply transmitted voice directly with the aid of transducers (active sonar emitters; i.e., underwater loudspeakers) and were notorious for short range and poor intelligibility. Modern undersea acoustic communication systems translate the message into digital high-frequency active sonar pulses, which can be frequency agile for security (see above). Data rates well over one thousand bits per second, over ranges up to thirty nautical miles, can be achieved routinely.
Halocline: an area of the ocean where salt concentration changes, either horizontally or vertically. Has important effects on sonar propagation and on a submarine’s buoyancy.
Hertz (or Hz): cycles per second; applies to sound frequency, radio frequency, or alternating electrical current (AC).
Hole-in-ocean sonar: a form of passive (listening-only) sonar that detects a target by how it blocks ambient ocean sounds from farther off. In effect, hole-in-ocean sonar uses an enemy submarine’s own quieting against it.
Hydrophone: an underwater sound listening device. In essence, a hydrophone is a special microphone placed in the water. The signals received by hydrophones are the raw input to passive (listening-only) sonar systems. Signal-processing computer algorithms then continually analyze this raw data to produce meaningful tactical information — such as a firing solution (see above).
INS: Inertial Navigation System. A system for accurately estimating one’s position, based on accelerometers that determine from moment to moment in what direction one has traveled, and at what speed.
Instant ranging: a capability of the new wide-aperture array sonar systems (see below). Because each wide-aperture array is mounted rigidly along one side of the submarine’s hull, sophisticated signal processing can be performed to “focus” the hydrophones at different ranges from the ship. The target needs to lie somewhere on the beam of the ship(i.e., to either side) for this to work well.
IR: infrared; refers to systems that make it possible to see in the dark or detect enemy targets by the heat that objects give off or reflect.
ISLMM: Improved Submarine-Launched Mobile Mine. A new type of mine weapon for American submarines, based on modified Mark 48 torpedoes and launched through a torpedo tube. Each ISLMM carries two mine warheads that can be dropped separately. The ISLMM’s course can be programmed with way points (course changes) so that complex coastal terrain can be navigated by the weapon, and/or a minefield can be created by several ISLMMs with optimum layout of the warheads.
Isothermal: a layer of ocean in which the temperature is very constant with depth. One example is the bottom isothermal zone, where water temperature is just above freezing, usually beginning a few thousand feet down. Other examples are a surface layer in the tropics after a storm, when wave action has mixed the water to a constant warm temperature; and a surface layer near the Arctic or Antarctic in the winter, when cold air and floating ice have chilled the sea to near the freezing point.
Kampfschwimmer: German Navy “frogman” combat swimmers. The equivalent of U.S. Navy SEALs and the Royal Navy’s Special Boat Squadron commandos. (In the German language, the word kampfschwimmer is both singular and plural.)
KT: kiloton; a measure of power for tactical nuclear weapons. One kiloton equals the explosive force of one thousand tons of TNT.
LIDAR: Light Direction and Ranging. Like radar, but uses laser beams instead of radio waves. Undersea LIDAR uses blue-green lasers, because that color penetrates seawater to the greatest distance.
Littoral: a shallow or near-shore area of the ocean. Littoral areas present complex sonar conditions because of bottom and side terrain reflections, and the high level of noise from coastal shipping, oil-drilling platforms, land-based heavy industry, etc.
LMRS: Long-term Mine Reconnaissance System: A remote-controlled self-propelled probe vehicle, launched from a torpedo tube and operated by the parent submarine. The LMRS is designed to detect and map enemy minefields or other undersea obstructions, and is equipped with forward and side-scanning sonars and other sensors. Each LMRS is retrievable and reusable.
MAD: Magnetic Anomaly Detection. A means for detecting an enemy submarine by observing its effect on the always-present magnetic field of the earth. Iron anywhere within the submarine (even if its hull is nonferrous or de-Gaussed) will distort local magnetic field lines, and this can be picked up by sensitive magnetometers in the MAD equipment. Effective only at fairly short ranges, often used by low-flying maritime patrol aircraft. Some naval mine detonators also use a form of MAD by waiting to sense the magnetic field of a passing ship or submarine.
Megaton: a measure of power for strategic nuclear weapons. One megaton equals the explosive force of one million tons of TNT. (A megaton also equals one thousand kilotons.)
METOC: Meteorology and Oceanography Command. The part of the U.S. Navy that is responsible for providing weather and oceanographic data, and accompanying tactical assessments and recommendations, to the navy’s operating fleets. METOC maintains a network of centers around the world to gather, analyze, interpret, and distribute this information.
Naval Submarine League (NSL): A professional association for submariners and submarine supporters. See their Web site, www.navalsubleague.com.
Network-centric warfare: a new approach to war fighting in which all formations and commanders share a common tactical and strategic picture through real-time digital data links. Every platform or node, such as a ship, aircraft, submarine, Marine Corps or army squad, or SEAL team, gathers and shares information on friendly and enemy locations and movements. Weapons, such as a cruise missile, might be fired by one platform and redirected in flight toward a fleeting target of opportunity by another platform, using information relayed by yet other platforms — including unmanned reconnaissance drones. Network-centric warfare promises to revolutionize command, control, communications, and intelligence, and greatly leverage the combat power of all friendly units while minimizing collateral damage.
NOAA: National Oceanic and Atmospheric Administration. Part of the Department of Commerce, r
esponsible for studying oceanography and weather phenomena.
Ocean Interface Hull Module: part of a submarine’s hull that includes large internal “hangar space” for weapons and off-board vehicles, to avoid size limits forced by torpedo-tube diameter. (To carry large objects such as an ASDS minisub externally creates serious hydrodynamic drag, reducing a submarine’s speed and increasing its flow noise.) The first Ocean Interface has been ordered as part of the design of the USS Jimmy Carter, the last of the three Seawolf-class SSNs to be constructed.
PAL: Permissive Action Lock. Procedures and devices used to prevent the unauthorized use of nuclear weapons.
Photonics mast: the modern replacement for the traditional optical periscope. The first will be installed in the USS Virginia (see below). The photonics mast uses electronic imaging sensors, sends the data via thin electrical or fiber-optic cables, and displays the output on large high-definition TV screens in the control room. The photonics mast is “non-hull-penetrating,” an important advantage over older ’scopes with their long, straight, thick tubes that must be able to move up and down and rotate.
Piezo rubber: a hull coating that uses rubber embedded with materials that expand and contract in response to varying electrical currents. This permits piezo-rubber tiles to be used to help suppress both a submarine’s self-noise and echoes from enemy active sonar (see active out-of-phase emissions, above).
Pump jet: a main propulsor for nuclear submarines that replaces the traditional screw propeller. A pump jet is a system of stator and rotor turbine blades within a cowling. (The rotors are turned by the main propulsion shaft, the same way the screw propeller’s shaft would be turned.) Good pump-jet designs are quieter and more efficient than screw propellers, producing less cavitation noise and less wake turbulence.
Quieting: design techniques and technologies used to minimize the amount of noise a submarine transmits into the surrounding water. Since quieting is crucial to stealth, the most advanced methods are highly classified. Techniques include placing internal decks on “rafts” that float on springs or flexible pivot joints in order to isolate internal sounds and vibrations from the outer hull. Equipment may also be mounted on noise-insulating materials, such as rubber blocks or bladders filled with oil. Quieting can also include disciplined behavior by the submarine’s crew, for instance not slamming hatches, not dropping tools on the deck, and not operating some devices or equipment at all when quieting is most essential.
Radiac: Radiation Indications and Control. A device for measuring radioactivity, such as a Geiger counter. There are several kinds of radiac, depending on whether alpha, beta, or gamma radiation, or a combination, is being measured.
ROEs: Rules of Engagement. Formal procedures and conditions for determining exactly when weapons (including “special weapons” such as nuclear devices) may be fired at an enemy.
SEAL: Sea Air Land. U.S. Navy Special Warfare commandos. (The equivalent in the Royal Navy is the SBS, Special Boat Squadron.)
7MC: a dedicated intercom line to the Maneuvering Department, where a nuclear submarine’s speed is controlled by a combination of reactor-control-rod and main steam-throttle settings.
Sonobuoy: a small active (“pinging”) or passive (listening-only) sonar detector, usually dropped in patterns (clusters) from an aircraft or a helicopter. The sonobuoys transmit their data to the aircraft by a radio link. The aircraft might have on-board equipment to analyze this data, or it might relay the data to a surface warship for detailed analysis. (The aircraft will also carry torpedoes or depth charges in order to be able to attack any enemy submarines that its sonobuoys detect.) Some types of sonobuoy are able to operate down to a depth of sixteen thousand feet.
SOSUS: Sound Surveillance System. The network of undersea hydrophone complexes installed by the U.S. Navy and used during the Cold War to monitor Soviet submarine movements (among other things). Now SOSUS refers generically to fixed-installation hydrophone lines used to monitor activities on and under the sea. The Advanced Deployable System (ADS) is one example: disposable modularized listening gear designed for rapid emplacement in a forward operating area. After the Cold War, some SOSUS data has been declassified, proving of immense value for oceanographic and environmental research.
Sound-ray traces: a display of the paths in which spreading sound waves will be bent and reflected underwater in a particular area. Ray traces are estimates, based upon calculations using information on local ocean temperature and salinity at different depths. Sound-ray trace information can be used to help a submarine find the best place to hide from enemy detection platforms. In addition, this information can be applied in interpreting noises detected coming through the water from an enemy submarine in order to help determine the hostile sound source’s likely bearing, range, depth, and even its course and speed.
Sound short: a failure of a submarine’s quieting (see above), in which noise from within the sub is transmitted into the surrounding sea. Sound shorts are very serious matters, since they can ruin stealth and lead to detection and attack by an enemy. A submarine’s sonars are able to check it for sound shorts, and if any are found the crew will give a priority to correcting them. Often this can be done by repairing or replacing faulty quieting gear, or if necessary by switching off the machinery that is causing the unwanted noise — although the latter may put the submarine at a grave tactical disadvantage, if the errant machinery is needed for full war-fighting readiness.
SSGN: a type of nuclear submarine designed or adapted for the primary purpose of launching cruise missiles, which tend to follow a level flight path through the air to their target. An SSGN is distinct from an SSBN, which launches strategic (hydrogen-bomb) ballistic missiles, following a very high “lobbing” trajectory that leaves and then reenters earth’s atmosphere. Because cruise missiles tend to be smaller than ballistic missiles, an SSGN is able to carry a larger number of separate missiles than an SSBN of the same overall size. Note, however, that since ballistic missiles are typically “MIRVed” — i.e., equipped with multiple independently targeted reentry vehicles — the total number of warheads on an SSBN and SSGN may be comparable; also, an SSBN’s ballistic missiles can be equipped with high-explosive warheads instead of nuclear warheads. (A fast-attack submarine, or SSN, can be thought of as serving as a part-time SSGN, to the extent that some SSN classes have vertical launching systems for cruise missiles and/or are able to fire cruise missiles through their torpedo tubes.)
Subtropical convergence: the area in the South Atlantic Ocean where currents of warmer water from near the equator meet and clash with other currents of colder water from near the Antarctic. The result is a zone of unpredictable and confusing sonar conditions. The subtropical convergence does not extend across the South Atlantic as a well-defined straight line, but rather is a broad area that snakes across different latitudes in different places and varies over time.
Thermocline: the region of the sea in which temperature gradually declines with depth. Typically the thermocline begins at a few hundred feet and extends down to a few thousand feet, where the bottom isothermal zone is reached (see above).
TMA: Target Motion Analysis. The use of data on an enemy vessel’s position over time relative to one’s own ship in order to derive a complete firing solution (see above). TMA by passive sonar alone, using only relative bearings to the target over time — and instant ranging data where available (see above) — is very important in undersea warfare.
Tonal: sound given off at a single frequency, similar to a pure musical “tone” or note. Tonals are important in detecting and identifying passive sonar contacts. This is because different equipment — and thus different classes of friendly and enemy submarines carrying that equipment — have unique sets of frequencies at which they emit tonals. One example of the source of a tonal might be an item of equipment that rotates at a particular rate per second, such as a turbogenerator, a reactor cooling-water circulation pump, or even a food blender in the ship’s galley (kitchen).
Towed array: a long cable equipped with hydrophones (see above) trailed behind a submarine. Towed arrays can also be used by surface warships. The towed array has two advantages: Because it lies behind the submarine’s stern, aft of self-noise from the propulsion plant, it is able to listen in directions where the submarine’s on-hull sonars are “blind.” Also, because the towed array is very long (as much as a mile), it is able to detect very long-wavelength (very low-frequency) sounds — which smaller, on-hull, hydrophone arrays may miss completely. Recently, active towed arrays are being introduced. These are able to “ping” as well as listen at very low frequencies, which has significant tactical advantages in some sonar and terrain conditions. The next planned advance is a towed array with three or more separate parallel lines in which the individual hydrophones use fiber-optic coils and lasers. Tiny changes in the behavior of the laser light will result when the coils are influenced by sound waves in the surrounding ocean. Analysis of such data promises to greatly increase the sensitivity of the array to the presence of enemy submarines and other targets. (When not in use, the towed array is retracted by winches in the submarine’s hull. Towed arrays often need to be retracted if the submarine is in close proximity to bottom terrain or surface shipping, or if the submarine intends to move at high speed.)
