Abstract: A pneumatic spear gun (11) comprising a barrel (27) having an open end (33) through which a shaft (15) of a spear (13) can be received. A first piston (35) is slidingly and sealingly received in the barrel (27) for movement towards and away from a retracted position. A retaining means (41) is provided for releasably retaining the piston (35) in the retracted position. A source of compressible fluid such as air is contained in a reservoir (59) and is arranged to undergo compression upon movement of the piston (35) into the retracted position and to propel the piston along the barrel (27) from the retracted position upon release of the piston thereby to propel the spear (13). A control means is provided for selectively increasing the pressure of the compressible fluid for varying the propulsive force applied to the piston (35). The control means includes a cylinder (43) forming part of the resevoir (59) and having a second piston (45) slidingly and sealingly mounted therein.