Abstract: An apparatus which allows the installation of a relatively inexpensive, low-attenuation, subterranean fiber optic cable underwater is disclosed. A high-density polyethylene subduct is extruded around the fiber optic cable to form a subduct assembly which typically exhibits a weight that is less than its buoyancy in water. The subduct assembly is then transported to the point of installation along with at least one sinkable cable and a lashing wire. Dimensions of the sinkable cable are selected so that, at the point of installation, the sinkable cable is lashed to the subduct assembly to form a cable assembly having a desired weight-to-buoyancy ratio with respect to water and a desired tensile strength. Splices in the subduct assembly and the sinkable cable occur at locations in the cable assembly which are offset from one another.