Abstract: An underwater gun comprises a multi-chambered head attached to a long handle. The handle includes a rotatable section connected to the head to manually index the cylinder, sequentially chamber by chamber, into the firing position. Spring urged arms retain the cylinder in the head but with the turn of a cylinder lock ring open to permit removal and replacement of the cylinder underwater as well as above. Cartridges are held securely in the cylinder and replacement cylinders by threaded shell retainers. The extra pre-loaded cylinders can be carried by the diver underwater to reload the gun after the first cylinder has been emptied.