Fathom — Unit of depth equal to six feet.
Fathometer — Bottom sounding sonar that directs an active sonar pulse down to the ocean bottom and measures the time for the pulse to reflect back and hence the distance to the bottom. New units transmit a secure pulse, using a short duration random high frequency pulse.
Final Bearing and Shoot — Order of the captain to shoot a torpedo after he takes one last periscope observation of a surface target.
Firecontrol Solution — A contact’s range, course, and speed. A great mystery when using passive sonar. Determining the solution requires maneuvering one’s own ship and doing calculations on the target’s bearing rate. Can be obtained manually or with the firecontrol computer.
Firecontrol System — A computer system that accepts input from the periscope, sonar, and radar (when on the surface) to determine the firecontrol solution. The system also programs, fires, steers, and monitors torpedoes. If a ship is cruise missile equipped, the system will program and fire the missile.
Firecontrol Team — A collection of people whose task is to put a weapon on a target. Includes the sonar operators, OOD, JOOD, Captain, XO, firecontrol operators on Pos One, Pos Two, Pos Three, the firing panel, and the manual plotters (geographic, time-bearing, time-range, and time-frequency).
Firing Panel — A console section between Pos Two and Pos Three. The vertical section is a tube weapon status panel. The horizontal section has the trigger, a lever used to fire a torpedo or cruise missile.
Firing Point Procedures — An order by the captain to the firecontrol team to tell them to prepare to fire the weapon, done during a deliberate approach when the solution is refined, as opposed to a Snapshot. The solution is locked into the weapon and the ship is put into a firing attitude.
Fix — A ship’s position. Determined by visual triangulation or radar when close to land on the surface, or by NAV SAT or BE sonar when at sea.
Flag Plot — A chart room used by flag officers (admirals) to plot strategy or determine the distribution of forces.
Flank Speed — Maximum speed of a U.S. submarine. Requires fast speed reactor main coolant pumps and running at 100 % reactor power.
FLASH — The highest priority of a radio message. Receipt required within minutes or seconds.
Forced Circulation — Forced flow of water coolant through a reactor using pumps, as opposed to natural circulation.
G — A measure of acceleration. The acceleration due to gravity is one g. Two g’s is twice, etc.
Geographic Plot — (1) A manual plot saved from World War II submarine days using the plot table to deduce a firecontrol solution. Works well on unsuspecting targets. Target zigs cause confusion on this plot. Useless in a melee situation. (2) A mode of display of the Mark I firecontrol system showing a God’s eye view of the sea with own ship at the center and the other contacts and their solutions surrounding it.
GMT (Greenwich Mean Time) — A worldwide time standard using the time at longitude zero at Greenwich, England. Also called Zulu time.
GPS (Global Positioning System) — A series of satellites and shipborne receivers enabling extremely precise navigation fixes. Also called the NAV SAT
Gyro/ Gyroscope — Electrical compass using a rapidly spinning gyroscope.
Head — Seagoing term for bathroom.
Helm — The wheel that turns the ship’s rudder. Also short for helmsman.
Hovering System — A depth control system managed by a computer that keeps the ship in one point underwater. Used by boomers when launching missiles. Used by fast attack submarines to establish a desired vertical speed (depth rate) to vertical surface through polar ice.
Hull Array — One of the sonar hydrophone element assemblies (arrays) of the BAT EARS sonar suite, consisting of multiple hydrophones placed against the skin of the hull over about one-third of the ship’s length. Used mostly as a backup to the spherical array because the hull array’s sensitivity is reduced by own ship noise inside the hull.
HUMINT — Human intelligence, that gained from foreign agents or American intelligence officers.
IR — Infrared.
JOOD — Junior Officer of the Deck; Assistant to the OOD. When in transit, the JOOD is usually an unqualified officer in a training position, given the Conn and supervised by the OOD.
KH-17 — Newest generation of Bigbird spy satellites. The KH stands for Keyhole — appropriate for a spy platform.
LAMPS — Light airborne multipurpose system. Cute acronym for a Seahawk ASW helicopter carried aboard a U.S. Navy surface ship.
Leg — The straight line travel of a submarine doing passive sonar Target Motion Analysis (TMA) between maneuvers. During a leg the crew attempts to establish a steady bearing rate to the target and establish speed across the line-of-sight to the target. Two legs determine a firecontrol solution. Three legs confirm the solution. Four legs indicate the captain is afraid to shoot. A large sign at Prospective Commanding Officer School in Groton, Connecticut, reads “you don’t need another GODDAMNED LEG!”
List — Tilt of a ship to the side.
Locking In/ Locking Out — Entering or leaving a submerged submarine through the escape trunk (airlock).
Lookaround — (1) A periscope observation. (2) A warning by the OOD or captain to the ship control team that the periscope is about to be raised. The Diving Officer and helmsman report ship’s speed and depth as a reminder, since high speeds can rip the periscope off and flood the ship through the periscope hole.
MAD (Magnetic Anomaly Detector) — A detector flown on an aircraft that measures changes in the earth’s magnetic field that could be caused by the iron hull of a submarine.
Main Ballast Tank — Tank that is used solely to hold seawater ballast, weight that allows a ship to sink, or, when blown, allows a ship to be light enough to surface.
Main Engines (Propulsion Turbines) — The large turbines that extract energy from steam and convert it to power to turn the screw.
Main Steam Valves One and Two (MS-1, MS-2) — Large gate valves on the port and starboard main steam headers, at the forward bulkhead of the aft compartment. These can isolate the main steam system in the event of a major steam leak.
Maneuvering — The nuclear control room, located in the aft compartment upper level. Smaller than most closets.
Maneuvering Watch — The watch stations manned when a ship gets underway in restricted waters.
Mark 36 or 38 — A torpedo-sized decoy vehicle that transmits the sounds of a submarine and can be programmed to maneuver through the ocean like a submarine; used to evade a trailing hostile ship or torpedo.
Mark 50 — Latest breed of torpedo. Also called the “Hullcrusher.”
Mark 80 SLAAM — Submarine-launched anti-air missile.
Mark On Top — Term used to note that a hostile aircraft is flying directly over the submarine. Generally means the submarine has been detected by the aircraft and will be under attack almost immediately. Usually followed by an expletive, i.e. “P-3 mark on top, dammit.”