TARGET ONE The designation of a sonar, radar, ESM, or visual contact as a target to be fired upon or tracked.
TARGET ZIG A term used to describe a target’s maneuver, either a turn, speed change, or both. Requires the ship to do more TMA to get a new solution.
TDU (TRASH DISPOSAL UNIT) A vertical torpedo tube used to jettison garbage overboard. Garbage is first bagged and weighed down with lead bricks to ensure it does not float to the surface and give away the ship’s position.
TERMINAL VELOCITY A falling or accelerating object in a fluid (air or water) eventually stops speeding up when fluid drag balances accelerating force. The velocity that is reached is called terminal velocity.
TEST DEPTH A depth about 2/3 of crush depth. Maximum allowed depth a submarine is allowed to go in peacetime.
TG’S (TURBINE GENERATORS) The two turbines aft that turn the ship’s electrical generators and provide electrical power.
THERMAL LAYER A layer of warm water near the surface of the ocean. The water is warm because of agitation by waves and sunlight. Further down, the wave motion is nil and there is no sunlight, leaving the seawater near freezing at all times. Sound waves originating below the layer bounce off it and come back down, making it difficult for surface ships to detect deep submarines, and the reason surface ships use dipping sonars or deep towed arrays. Sound waves originating above the layer will bounce off the layer and come back up, making surface ships difficult for submarines to hear when approaching the surface to come to periscope depth. Sometimes the layer confines surface noise into sound channels, enabling a submarine to hear a contact above the layer hundreds of miles away. Layer depth is typically 150 to 200 feet deep.
THERMAL NEUTRONS Neutrons slowed by water moderator in a reactor core, enabling them to be absorbed by another uranium nucleus to cause fission.
THERMAL STRESS Stress in metal caused by one side being hot and the other being cold. The hot part wants to expand, the cold part wants to contract, and the result is the metal trying to tear itself apart. An example is a rapid heatup of the massive metal of a reactor pressure vessel when raising plant water temperature after a scram. The inside surface of the vessel can be 500 degrees, while the outside and the “meat” of the thick metal is still at 300 degrees. The vessel can rupture, causing a loss-of-coolant accident. Neutron embrittlement of the vessel makes thermal stress effects even worse.
THERMOLUMINESCENT DOSIMETER (TLD) A small piece of plastic worn on a crewmember’s belt to measure that person’s radiation dose.
THREE-WAY VALVE A valve, usually a ball valve, that can direct inlet flow one of two ways.
THROTTLE The valves at the inlet of a steam turbine that determine how much steam flow the turbine will receive, and thus, the amount of power the turbine will produce (and its speed). Done at the Steam Plant Control Panel.
THROTTLEMAN Nuclear trained enlisted watchstander who monitors the steam plant at the Steam Plant Control Panel and positions the throttle based on the speed orders of the control room (which are transmitted by the engine order telegraph).
TIME-BEARING PLOT A large graphical plot of target bearing versus time. Plot can be used to calculate contact range based on knowledge of own ship’s speed across the line-of-sight. Also used to call or verify a target zig when target bearing rate diverges from expected bearing rate.
TIME-FREQUENCY PLOT A large graphical plot of target tonal frequency versus time. Useful in zig detection, when a down shifted frequency shows the target moving away and an upshift shows the target turning toward own ship.
TITANIUM A special metal with high strength that is useful in submarine hulls due to its creep properties. Very expensive and almost impossible to weld.
TMA (TARGET MOTION ANALYSIS) Means of establishing a target solution using passive sonar. Own ship does maneuvers to generate speed first on one side of the line-of-sight, then on the other. Several maneuvers or legs can quickly find the target solution. Stealthy method of determining what the target is doing. The system is weak when the target is himself doing TMA. Result is a melee or PCO Waltz, where both submarines are maneuvering and neither knows what the other is doing. In worst case, submarines may need to shift to active sonar to determine range or clear datum until the target can be ambushed stealthily.
TONAL A steady sound frequency emitted by a target submarine. Usually very narrow bandwidth. Very much like the pure tone put out by a tuning fork. Caused by rotating machinery such as turbine generators.
TONAL SEARCH GATE A filter set up on a narrowband passive sonar that only listens to a small range of sound frequencies in anticipation of finding a particular tonal.
TOP SECRET Classification of information, the disclosure of which could “cause grave damage to the national security of the United States.” Detailed information regarding U.S. warplans and some U.S. OPS. Old submarine saying: confidential on the table, secret on the bed, top secret under the pillow.
TOP SECRET — THUNDERBOLT When the classification of top secret is followed by a codeword, it indicates the SCI classification, making the information classification essentially higher than top secret. Usually the very name of the classification is at least secret.
TOPSOUNDER A sonar transducer designed to transmit an active sonar beam upward to gauge the thickness of the ice cover overhead.
TORPEDO IN THE WATER Announcement that a hostile submarine has launched a weapon at own ship, requiring immediate evasive action and a counterfire.
TOWED ARRAY A passive sonar hydrophone array towed astern of a submarine on a cable up to several miles long. The array itself may be a thousand feet long. The array is used to detect narrowband tonals at extreme ranges.
TRACK To keep tabs on a contact’s solution over time. Merchant surface vessels are tracked to avoid collision. A casual maintenance of a fire-control solution to a contact.
TRAIL The serious prosecution of a target intended to maintain weapons ready to fire at the target at all times while remaining undetected. The constant maintenance of an accurate fire-control solution to an enemy submarine. Trail ranges vary from 10,000 yards to 20 yards. The trick is to keep from being counterdetected, which can be embarrassing. U.S. attack submarines will keep Russian boomers in trail as much as possible to ensure they can be sunk if they get ready to fire ballistic missiles. Second priority for trailing is a Russian attack sub. Third priority is another U.S. unit, to see if they can be trailed without their knowledge. Trailing a U.S. unit is extremely difficult unless they are making transient noises or have broken equipment.
TRANSCEIVER Refers to radio equipment or sonar equipment that can both receive and transmit.
TRANSDUCER A sonar hydrophone that can ping active sonar pulses and listen and analyze the returning pulses.
TRANSIENT A noise that is made by an enemy sub due to a temporary condition. Examples include dropped wrenches, boots clomping on deckplates, slamming hatches, boiler blowdowns, rattling check valves, etc.
TRIM The balance of a submarine. The first step is to pump or flood variable ballast to achieve neutral buoyancy. The second is to pump from tank to tank to balance the ship fore and aft and port to starboard.
TRIM PUMP A large pump that can pump variable ballast from tank to tank or from a tank to the sea to achieve a good trim. Can be connected to the drain system for use as a backup for the drain pump.