This invention relates to the mechanical construction of torpedo-boats of the class wherein the hull proper is submerged, but supported at a suitable distance below the surface by a float, the main objects of the invention being to provide for the protection of the float in case obstructions are encountered as the boat is advanced in action, and to provide for the safe storage and support of the sinal-lights; and to the ends named the invention consists, essentially, of a hull that is provided with a float and guard-arms that extend above the float and are adapted to support signal-lights.