Maritime Glossary
This glossary serves as a comprehensive reference for both the general public and academic researchers interested in WWII submarine signaling, MF-DF technology, and broader naval history. It bridge the gap between technical maritime terminology and the specialized language of underwater warfare.
A
Abaft – Toward the stern (rear) of a ship.
Abeam – At a right angle to the ship’s centerline.
Aft – The rear portion of a vessel.
Anchor – A heavy object used to secure a vessel to the seabed.
Astern – Behind the ship.
B
Ballast – Weight (often water) used to stabilize a vessel.
Beam – The width of a ship at its widest point.
Bearing – Direction to an object, measured in degrees.
Bilge – Lowest internal part of a ship’s hull where water collects.
Bridge – Command center of a ship.
Bulkhead – Internal vertical partition within a ship.
Buoy – Floating marker used for navigation.
C
Chart – A nautical map.
Cleat – Fitting used to secure ropes.
Compass – Instrument used to determine direction.
Conning Tower – Raised structure on a submarine used for observation and control.
Course – Intended direction of travel.
Crew Complement – Total number of personnel aboard.
D
Dead Reckoning – Navigation based on speed, time, and direction from a known position.
Deck – Horizontal surface (floor) of a ship.
Displacement – Weight of water displaced by a vessel (i.e., its effective weight).
Draft (Draught) – Depth of a ship below the waterline.
E
Ensign – National flag flown by a vessel.
Engine Room – Compartment housing propulsion machinery.
F
Fathom – Unit of depth equal to 6 feet (≈1.83 m).
Freeboard – Distance between waterline and deck edge.
G
Galley – Kitchen aboard a vessel.
Gangway – Passage or boarding ramp.
H
Heading – Direction the ship is pointing.
Hull – Main body of a vessel.
K
Keel – Central structural backbone of a ship.
L
Latitude – Angular distance north or south of the equator.
Longitude – Angular distance east or west of Greenwich.
Log – Record of a vessel’s voyage and operations.
M
Mast – Vertical structure supporting equipment or sails.
Midships – Central part of a vessel.
Mooring – Securing a vessel in place.
P
Port – Left side of a ship when facing forward.
Propeller – Rotating device that drives a ship forward.
S
Starboard – Right side of a ship when facing forward.
Stern – Rear of a vessel.
Superstructure – Structures above the main deck.
T
Tonnage – Measurement of cargo capacity or internal volume.
⚓ WWII Submarine & Naval Warfare Terms
A
Acoustic Torpedo – Torpedo that homes in on sound, such as propeller noise.
ASDIC – Early sonar system used by Allied ships (British term).
Attack Periscope – Smaller periscope used during combat for minimal visibility.
B
Battery Compartment – Section containing batteries for submerged propulsion.
Blow Ballast – Expelling water from ballast tanks to surface.
C
Crash Dive – Rapid submergence in response to threat.
Convoy – Group of ships traveling together for protection.
D
Depth Charge – Explosive dropped into water to destroy submarines at depth.
Diesel-Electric Propulsion – Submarine system using diesel engines on surface and batteries underwater.
E
Enigma – German cipher machine used for encrypted communication.
H
Hydrophone – Underwater microphone used to detect ships.
M
MF/DF (Medium Frequency Direction Finding) – Radio direction-finding system used to locate enemy transmissions, especially U-boats.
Magnetic Pistol – Torpedo detonator triggered by magnetic field beneath a ship.
P
Periscope – Optical device allowing a submerged submarine to see above water.
Pressure Hull – Inner hull designed to withstand underwater pressure.
S
Schnorchel (Snorkel) – Device allowing diesel engines to run while submerged at periscope depth.
Silent Running – Operating a submarine as quietly as possible to avoid detection.
Sonar – Sound Navigation and Ranging; system for detecting underwater objects.
T
Torpedo – Self-propelled underwater weapon.
Torpedo Tube – Launch system for torpedoes.
Trim – Balance of a submarine fore and aft.
U
U-boat – German submarine (“Unterseeboot”).
W
Wolfpack – Coordinated group of submarines attacking convoys.
Additional Relevant Terms
Bathysphere – Early deep-sea exploration vessel.
Chart Datum – Reference level for measuring sea depths.
Deadlight – Cover for a porthole used in heavy seas or combat.
Drift – Movement caused by current or wind.
Gyrocompass – Compass using Earth’s rotation rather than magnetism.
Hard-a-Starboard – Order to turn sharply right.
Knot – Unit of speed (1 nautical mile per hour).
Lee Shore – Shore downwind of a vessel (dangerous).
Nautical Mile – Distance equal to 1.852 km.
Scuttle – To deliberately sink a vessel.
Sounding – Measuring water depth.
Wake – Disturbed water behind a moving vessel.