4. =Armour Backing.=--A thick layer of teak which acts as a cushion behind the armour and to which it is secured. 5. =Bulkhead Armour.=--Vertical armour in the interior of the ship, placed across it from side to side. =ASTERN.=--The opposite to ahead. =ASTERN FIRE.=--The discharge of guns along the line of the keel directly astern of a vessel. =ATHWARTSHIPS.=--At right angles to the keel. =AUXILIARY.=--A ship--not necessarily a fighting ship--which forms a component part of a Fleet. These include Repair vessels, Hospital ships, Depôt, Submarine and Destroyer Mother-ships, Colliers, etc. =AUXILIARY ENGINES.=--The machinery employed for boat-hoisting, pumping, electric lighting, refrigerating, ventilating, and other purposes on board ships. =BACKSTAYS.=--Ropes stretched from a mast or topmast head to the sides of a vessel--some way abaft the mast--to give support to the mast and prevent it going forward. =BALLAST.=--Weighty material placed in the bottom of a ship to give her “stiffness”; that is, to increase her tendency to return to the upright position when inclined or heeled over by the force of the wind or other cause. =BALLISTICS.=--That branch of science particularly devoted to the theory of gunnery. =BARBETTE.=--The steel platform or mounting on which a power-worked gun rests and within which it revolves. =BARGE.=--A general term given to flat-bottomed boats. The _Admiral’s_ (or _Captain’s_) Barge is usually a special steamboat belonging to a warship reserved for the use of the Admiral or Captain. =BATTEN.=--Long strips of wood used for various purposes. =To batten down.=--To cover up and fix down, usually spoken of hatches when they are covered over in rough weather. =BATTERY.=--That portion of a ship’s armament inside the citadel. The entire armament is frequently spoken of as a “battery.” =BATTLE CRUISER.=--A vessel combining the speed and other essential qualities of a cruiser with an armament and protection sufficient to enable her to take her place in the fighting-line beside the battleships. =BATTLE PRACTICE.=--An annual practice carried out in the Navy, to test the battle or fighting efficiency of the component parts of a ship’s armament. =BATTLESHIP.=--A ship specially designed to take and give the hard knocks of a Fleet action. =BEAK.=--The extreme fore part of a vessel. =BEAM.=--The widest measurement across a ship. =BEARINGS.=--This word properly belongs to the art of navigation, in which it signifies the direction (by compass) in which an object is seen. =BEFORE.=--Forward or in front of; the opposite to abaft. =BERTHON BOAT.=--A collapsible boat used in destroyers and small craft. =BETWEEN DECKS.=--In a vessel of more than one deck, to be between the upper and the lower. =BINNACLE.=--The fixed case and stand in which the compass in any vessel is placed. =BLOCKADE.=--So to besiege a port that no communication can take place from seaward.