This Recommendation is concerned with the system performances and interface requirements of repeatered optical fibre submarine cable systems using optical line amplifiers (OFAs) as line repeaters. It covers the aspects related to single wavelength systems (SWS)@ wavelength division multiplexing systems (WDMS) and dense wavelength division multiplexing systems (DWDMS). Depending on the system specifications@ such as the number of terminations@ the connectivity@ the total capacity@ the maximum end-to-end distance@ and/or the system cost@ one of these three types of systems may be more appropriate to guarantee the system requirements. A high data capacity may be carried by one wavelength using a high data bit-rate@ or by several wavelengths using a smaller one. From a general point of view@ the characteristics@ performance specifications and requirements of the submerged equipment are mostly identical for SWS@ WDMS and DWDMS. Indeed@ SWS appears as a specific case of WDMS using one wavelength and@ in turn@ WDMS can be considered as a specific case of DWDMS with a small number of wavelengths. As a consequence@ general statements mentioned in this Recommendation can be applied to SWS@ WDMS and DWDMS. However@ when necessary@ more detailed Recommendations will highlight the specificity of these three types of systems. Common implementation aspects of optical submarine cable systems for manufacturing@ installing and maintenance are described in [ITU-T G.971]. [ITU-T G.978] contains common aspects of the characteristics of the optical fibre submarine cables. [ITU-T G.979] is also concerned with the characteristics of monitoring systems for optical fibre submarine cable systems with repeaters. The physical implementation of optically amplified fibre submarine systems is considered in Annex A.