A visual indicator assembly for use with an underwater mine system comprises a surface position marker (11) having a buoyancy device (23), the marker (11) being adapted to provide visual and/or audible indications on the surface that a mine has been "fired". The assembly further comprises a support device (13) for supporting the marker (11) underwater and a severable coupling (37) which, when severed, releases the marker (11) to float to the surface. The assembly further comprises a release means selectively operable to sever the coupling (37) and to release the marker (11) to float to the surface.