Abstract: The invention relates to an apparatus for damping vibrational deflections of periscopes or other vessel devices, which periscopes or other vessel devices extend into an aqueous medium when in use. Particular uses for the damping apparatus include application to periscopes, antennas and the like, for submarines. The damping apparatus preferably comprises a damping mass suitably mounted on a periscope or other extended-in-use device by damping elements. The damping elements may include, for example, elastic springy elements having a high internal friction, friction dampers, and coil springs which dissipate vibrational energy. The damping mass moves in response to vibrations of the damped device, thereby functioning as a kinetic energy storing device. The damping elements interact with the movement of the damping mass and thereby function as potential energy storing means.