Armament, Matériel, Munitions, Arms, Ordnance, Artillery and Ammunition as used in modern warfare are not all synonyms of one another, but they are frequently confused.
In general they mean material used in military, naval, and air operations.
Armament is by far the most inclusive term, for it comprehends everything that must be considered in determining a nation's military strength, such as trained soldiers, sailors, and fliers, land fortifications, battleships and all other war vessels (as transports, submarines, destroyers), aircraft, guns, provisions, equipment, available manpower and resources.
Materiel is less inclusive; it comprehends materials only and includes all the requirements of a military establishment other than personnel.
Munitions is often coextensive with matériel but typically stresses supplies of war including military equipment of all kinds, especially all weapons of attack and defense and the missiles, projectiles, and propellants necessary for their use.
Arms is less definite in its application than either of the preceding words, but in general, when used as an inclusive term, it covers whatever weapons soldiers or sailors need in actual fighting (as cannon, guns, rifles, pistols, swords, and bayonets).
Ordnance is used in two senses, the more general of which is probably the less common. In that sense the term includes not only everything which is covered by arms, but every other weapon of attack or defense (as tanks) and everything needed for the equipment and use of these weapons (as mounts, carriages, projectiles, and missiles) or for their manufacture or repair (as tools and machinery).
More narrowly and also more commonly, ordnance is a comprehensive term for all kinds of heavy firearms, especially those discharged from mounts (as cannon, guns, howitzers, and mortars).
Artillery is a close synonym of ordnance in this latter sense, but it suggests actual warfare and therefore implies group service in the management of mounted firearms. It sometimes, like the broader sense of ordnance, comprehends also the mounts, ammunition, and other items essential to the work of the branch of an army dealing with the operation of heavy guns (called also the artillery).
Ammunition, though once used as a general term nearly equal to munitions, is now restricted in its application to the projectiles used in warfare (as bullets, shells, grenades, or bombs) and their necessary propellants, detonators, fuses, and primers.