=MINE-SWEEPER.=--A ship whose duty it is to discover and destroy the enemy’s mines in order to leave a clear passage for friendly craft. =MOLE.=--A stone break-water or sea-wall. =MOOR.=--To anchor a ship with two anchors. =MOTHER-SHIP.=--A depot ship for torpedo craft, submarines, etc., victualling and issuing stores to the crews of the vessels under her command controlled by her officers. =MUZZLE ENERGY.=--The force which is propelling the projectile when it leaves the gun. =MUZZLE VELOCITY.=--The speed at which a projectile is travelling when it leaves the gun. =NAUTICAL MILE.=--One sixtieth of a degree of latitude. It varies from 6,046 ft. at the equator to 6,092 ft. in lat. 60° N. or S. The nautical mile for speed trials, generally called the Admiralty Measured Mile, = 6,080 ft., 1.151 statute miles, 1,833 metres. =NAVIGATION.=--That branch of science which teaches the sailor to conduct his ship from place to place. =NAVY LEAGUE, THE.=--A strictly non-party organisation formed in January, 1895, with Admiral of the Fleet, Sir G. Phipps Hornby, G.C.B., etc., as its first President, for the purpose of urging upon the Government and the electorate the paramount importance of a supreme Fleet as the best guarantee of peace. Its agencies are employed in all parts of the Empire spreading information on matters affecting the Royal Navy. =NUCLEUS CREW.=--The essential part of a crew of a ship such as the gun-layers, petty officers, etc. Some ships are manned by nucleus crews only, being completed to full strength in case of mobilisation. Such ships are sometimes colloquially known as “Nucoloid.” =OAKUM.=--The substance to which old ropes are reduced when unpicked. =OCEAN GOING DESTROYER.=--A large type of torpedo boat destroyer, specially designed for service in any wind or weather. =ORDNANCE.=--A general term applied to guns collectively, and to the Department concerned with them. =ORLOP DECK.=--The lowest deck in the ship. =PAY OFF.=--To end a “Commission.” =PENDANT OR PENNANT.=--A long, pointed flag. =Paying-off Pennant.=--A long streamer hoisted at the mainmast of a war vessel to denote she is “paying off.” =POOP.=--An extra deck on the after part of a vessel. =PORT.=--The left-hand side of the ship as you stand looking forward. =PRIMARY (or main) ARMAMENT.=--The largest guns mounted in a ship. =PRIZE.=--In war time, any vessel taken at sea from an enemy. =PROJECTED.=--A ship is said to be “projected” before keel plate is actually laid. =PROTECTIVE DECK.=--See “Armoured Deck.” =PROW.=--The beak or pointed cutwater of a ship. =Q.F. GUN.=--Quick-firing gun. A gun the cartridge of which is contained in a metal cylinder, as opposed to the B.L. gun.