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.
Isothermaclass="underline" 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.
Littoraclass="underline" 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, responsible 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).