ASDS: Advanced SEAL Delivery System. A new battery-powered mini-submarine for the transport of SEALs (see below) from a parent nuclear submarine to the forward operational area and back, within a warm and dry shirtsleeves environment. This permits the SEALs to go into action well rested and free from hypothermia — real problems when the SEALs must swim great distances, or ride while using scuba gear on older free-flooding SEAL Delivery Vehicle underwater “scooters.”
ASW: Antisubmarine warfare. The complex task of detecting, localizing, identifying, and tracking enemy submarines, in order to observe and protect against them in peacetime, and to avoid or destroy them in wartime.
Auxiliary maneuvering units: small propulsors at the bow and stern of a nuclear submarine, used to greatly enhance the vessel’s maneuverability. First ordered for the USS Jimmy Carter, the third and last of the Seawolf-class SSNs (nuclear fast-attack submarines) to be constructed.
Bipolar sonar: a form of active sonar in which one vessel emits the ping while one or more other vessels listen for target echoes. This helps disguise the total number and location of friendly vessels present.
CACC: Command and Control Center. The modern name for a submarine’s control room.
CAPTOR: a type of naval mine, placed on or moored to the seabed. Contains an encapsulated torpedo, which is released to home on the target.
CCD: Charge-Coupled Device. The electronic “eyes” used by low-light-level television, night-vision goggles, etc.
COB: Chief of the Boat (pronounced “cob”). The most senior enlisted man on a submarine, usually a master chief. Responsible for crew discipline, and for proper control of ship buoyancy and trim at battle stations, among many other duties.
Deep scattering layer: a diffuse layer of biologics (marine life) present in many parts of the world’s oceans, which causes scattering and absorption of sound. This can have tactical significance to undersea warfare forces by obscuring passive sonar contacts and causing false active sonar target returns. The layer’s local depth, thickness, and scattering strength are known to vary by many factors, including one’s location on the globe, the sound frequency being observed, the season of the year, and the hour of the day. The deep scattering layer is typically several hundred feet thick, and lies somewhere between one thousand and two thousand feet of depth during daylight, migrating shallower at night.
Deep sound channeclass="underline" a thick layer within the deep ocean in which sound travels great distances with little signal loss. The core (axis) of this layer is formed where seawater stops getting colder with increasing depth (the bottom of the thermocline, see below) and water temperature then remains at a constant just above freezing (the bottom isothermal zone, see below). Because of the way sound waves diffract (bend) in response to temperature and pressure, noises in the deep sound channel are concentrated and propagate for many miles without loss to surface scattering or seafloor absorption. Typically the deep sound channel is strongest between depths of about three thousand and seven thousand feet.
ELF: Extremely Low Frequency. A form of radio that is capable of penetrating seawater, used to communicate (one way only) from a huge shore transmitter installation to submerged submarines. A disadvantage of ELF is that its data rate is extremely slow, only a few bits per minute.
EMBT blow: Emergency Main Ballast Tank blow. A procedure to quickly introduce large amounts of compressed air (or fumes from burning hydrazine) into the ballast tanks in order to bring a submerged submarine to the surface as rapidly as possible. If the submarine still has propulsion power, it will also try to drive up to the surface using its control planes (called planing up).
EMCON: Emissions Control. Radio silence; also applies to radar, sonar, laser, or other emissions that could give away a vessel’s presence.
EMP: Electromagnetic Pulse. A sudden, strong electrical current induced by a nuclear explosion. This will destroy un-shielded electrical and electronic equipment and ruin radio reception. There are two forms of EMP, one caused by very high-altitude nuclear explosions, the other by ones close to the ground. (Mid-altitude bursts do not create an EMP.) Nonnuclear EMP devices, a form of modern nonlethal weapon, produce a similar effect locally by vaporizing clusters of tungsten filaments using a high-voltage firing charge. This generates a burst of hard X rays, which are focused by a depleted-uranium reflector to strip electrons from atoms in the targeted area, creating the destructive EMP electrical current. Other nonnuclear EMP weapons use bursts of microwaves emitted from special antennas.
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 celclass="underline" 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.