Voyage of the Devilfish

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.