A subsea data transmission cable for providing data communication with a subsea device installed at the ocean floor, comprising: - a first subsea cable section comprising at least one electrical data line, - a second subsea cable section comprising at least one fiber optic data line, - an intermediate conversion assembly, wherein one end of the first subsea cable section is terminated at the intermediate conversion assembly and wherein one end of the second subsea cable section is terminated at the intermediate conversion assembly, wherein the intermediate conversion assembly comprises: - a subsea housing, - a sealed chamber provided in the subsea housing, - a first termination assembly that terminates at least an outer sheath of the first subsea cable section; - a second termination assembly that terminates at least an outer sheath of the second subsea cable section; - a penetrator assembly (81, 82) configured to provide an electrical connection from within the sealed chamber to the at least one electrical data line and to provide an optical connection from within the sealed chamber to the at least one fiber optic data line, and - a conversion device disposed in the sealed chamber, the conversion device having an electrical interface to which the at least one electrical data line is connected and having an optical interface to which the at least one fiber optic data line is connected, wherein the conversion device is configured to convert an electrical data signal received at the electrical interface to an optical data signal for transmission via the optical interface, and to convert an optical data signal received at the optical interface to an electrical data signal for transmission via the electrical interface. - a first subsea cable section comprising at least one electrical data line, - a second subsea cable section comprising at least one fiber optic data line, - an intermediate conversion assembly, wherein one end of the first subsea cable section is terminated at the intermediate conversion assembly and wherein one end of the second subsea cable section is terminated at the intermediate conversion assembly, - a subsea housing, - a sealed chamber provided in the subsea housing, - a first termination assembly that terminates at least an outer sheath of the first subsea cable section; - a second termination assembly that terminates at least an outer sheath of the second subsea cable section; - a penetrator assembly (81, 82) configured to provide an electrical connection from within the sealed chamber to the at least one electrical data line and to provide an optical connection from within the sealed chamber to the at least one fiber optic data line, and - a conversion device disposed in the sealed chamber, the conversion device having an electrical interface to which the at least one electrical data line is connected and having an optical interface to which the at least one fiber optic data line is connected, wherein the conversion device is configured to convert an electrical data signal received at the electrical interface to an optical data signal for transmission via the optical interface, and to convert an optical data signal received at the optical interface to an electrical data signal for transmission via the electrical interface.