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.
Tonaclass="underline" 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.)