The aim of the invention is to devise a weapon (100) which has a completely modular design. For this purpose, the weapon (100) is subdivided into weapon-specific assemblies which are designed as carrier units of the components and/or of the modular assemblies of the weapon (100). A first assembly can be a modular weapon housing (3). Said weapon housing (3) consists of a carrier unit into which a breech system of the weapon (100) and its components are built. Another modular assembly is a weapon cradle (2). Into this modular assembly the weapon housing (3) module with breech system is integrated. The weapon housing (3) module can be complemented with the weapon barrel module. In a specific embodiment, the weapon barrel module is a weapon barrel bundle (10) with at least one weapon barrel (5, 5', 5''). Another modular assembly, a weapon drive (1), is connected to the weapon cradle (2). Said weapon drive comprises an external drive (1.1) and the breech drive (35, 36, 37). The components are connected to the modular assemblies and the modular assemblies to each other by means of rails and guides (15.1, 21.1) and complementary rails and guides (3.1, 3.2) for the assemblies (3), by binders (31) and holders (33), by pins (33, 34), bolts (31.1, 2.6) and quick release fasteners (22,.2). The weapon according to the invention is preferably an externally powered weapon (100).