The Bell System has conducted a system experiment as part of a program for developing technology for undersea lightwave systems. The experiment demonstrated repeater-less error-free transmission at 274 Mb/s over 101 km using single mode lightguide fiber and regenerator electronics all applicable for the undersea environment. The fiber meets all system requirements, including the high tensile strength needed for deep-sea applications. The regenerator is highly integrated and contains all functions needed for 274 Mb/s transmission. The fiber is of a depressed cladding design(1,2)and was prepared by the MCVD process in a joint program by Bell Telephone Laboratories and Western Electric.