FRAME Hoops of steel or titanium that serve as the skeleton for the pressure hull.
FRAME 57 The frame between the operations compartment and the reactor compartment on a Piranha class submarine. The start of the engineering spaces. Anything beyond Frame 57 is called “back aft.”
FREQUENCY GATE A narrow range of frequency that the sonar is tuned to listen to.
FUEL ELEMENT An assembly of uranium with zirconium cladding in a nuclear core. The uranium heats the water, making steam in the steam generators, allowing power production in the turbines.
FULL POWER LINEUP Electric plant lineup when the reactor is critical and self-sustaining. Both turbine generators are at 3600 RPM and are supplying power to the ship’s loads. The battery is not discharging.
FULL RUDDER When the rudder is turned 30 degrees.
FULL SCRAM When all control rods (not just the controlling group) are pushed to the bottom of the core. It takes much longer to recover from a full scram than a group scram.
FULL SPEED Maximum speed of a U.S. submarine with slow speed reactor main coolant pumps running the reactor at 50 % power. A Piranha class does about 25 knots at full.
FUSION A nuclear reaction in which several light nuclei come together and release tremendous quantities of energy. Usually requires initial temperatures of several thousand degrees.
G A measure of acceleration. The acceleration due to gravity is one g. Two g’s is twice, etc.
GAMMA RADIATION Electromagnetic radiation released in a nuclear reaction. Generally similar to X-rays.
GEOGRAPHIC PLOT (1) A manual plot saved from World War II submarine days using the plot table to deduce a fire-control 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 firecontro) 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.
GEOSYNCHRONOUS SATELLITE A satellite orbiting at an altitude of about 33,000 miles. The orbital velocity matches the earth’s rotational speed, making the satellite stationary with respect to the earth’s surface. Ideal for communication satellites.
GI-UK GAP (GREENLAND-ICELAND-UNITED KINGDOM GAP) The northern entrance to the Atlantic, choked by Greenland and Iceland to the northwest and Great Britain to the east. Any sortie of Russian Northern Fleet units would need to pass north of Norway, then south through the GI-UK gapGMT (GREENWICH MEAN TIME) A worldwide time standard using the time at longitude zero at Greenwich, England. Also called Zulu time.
GO CODE Slang for a nuclear release message to units ordered to fire nuclear weapons.
GPS (GLOBAL POSITIONING SYSTEM) A series of satellites and shipbome receivers enabling extremely precise navigation fixes. Also called the NAVSAT.
GRASS/RADAR GRASS A region within about 50 to 100 feet of the ground that surface search and air search radars are unable to penetrate due to ground clutter. An aircraft or missile flying in the grass can sneak up to its target without radar detection.
GREEN BAND Normal limits for T-AVE during critical reactor operation. Between 480 and 500 degrees IF.
GROUP ONE One of three control rod groups in a Naval S5W/S3G Core 3 core. During about half of core life these control rods control reactor temperature and power level.
GROUP SCRAM A reactor scram using only the few control rods in the controlling rod group. Enough negative reactivity to shut down the reactor for several hours, but not so much that recovery is difficult.
GUIDANCE WIRE A neutrally buoyant wire streamed from the rear of a Mark 49 or 50 torpedo allowing communication between the weapon and the fire-control system. Used to pass steer commands from ship to torpedo and information about the target from torpedo to ship, GYRO/GYROSCOPE Electrical compass using a rapidly spinning gyroscope.
HAFNIUM Element used in Navy control rods. Acts as a black hole for neutrons. Without neutrons, fission reactions stop, and a core is shutdown.
HALF POWER LINEUP Electric plant lineup when the reactor is critical and self-sustaining. One turbine generator is at 3600 RPM and supplying power to the ship’s loads. The battery is not discharging.
HARD RUDDER A rudder angle of about 37 degrees. An emergency order because it risks being unable to return the rudder to an amidships position.
HARDENED SAIL A sail constructed of 3 inch thick HY-80 steel designed to break through polar ice.
HEAVY WATER Deuterium. Used in nuclear fusion reactors or fusion (hydrogen) bombs.
HELM The wheel that turns the ship’s rudder. Also short for helmsman.
HF (HIGH FREQUENCY) Radio waves capable of reception continents away. Reception is often unreliable, susceptible to various atmospheric conditions.
HOMING A torpedo in the final stages of arming and pursuit of a target.
HOT RUN A serious emergency resulting from a torpedo that starts its engine while still in the tube or in the torpedo room. Hazards include the toxic gas exhaust and probability of warhead detonation.
HOT STANDBY A condition of a shutdown reactor and steam plant such that the systems are kept as warm as possible to allow a more rapid startup.
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 1/3 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.
HYDRAULICS Use of oil under pressure to cause motion in large equipment. Used to move the planes and rudder and to raise masts and antennae. In the nuclear plant, primary coolant (water) is used to move valves.
HYDRODYNAMIC FORCES Lift, downforce, or drag caused by the flow of water over the surface of a moving object.
HYDROPHONE A device that converts mechanical motion of soundwaves into electrical signals to be amplified and analyzed by the sonar system. Somewhat like a large microphone. A set of hydrophones forms an array. Hydrophones are passive devices designed for reception only. A transducer can either receive or transmit sonar pulses.
HY-80 STEEL A special alloy of steel made for the Navy. HY stand for high yield. 80 stands for yield stress of 80,000 psi. One of the strongest and toughest steels made. Used for the pressure hull plates and frames of the Piranha and Los Angeles classes.
IMMEDIATE The priority of a radio message just below FLASH. Receipt required within an hour.
IMPLOSION An inward explosion, such as a pressure hull crushed by seawater pressure.
INCLINOMETER A liquid filled tube in the shape of an upside down U with a small bubble at the top. A low-tech method to measure the angle or roll of the ship.
INDUCTION PIPING Piping from the snorkel mast to the ship for use by the diesel generator when the ship is snorkeling.