A subsea electrical-optical connector unit, comprising: a subsea housing containing at least a first chamber having a first port configured for connection to a subsea optical or electro-optical cable and a second, electrical input port; a media converter device mounted in the first chamber; a subsea electrical cable connector module connected to the second, electrical input port of the first chamber of the subsea housing and configured for releasable connection to an electrical ethernet cable, the subsea electrical cable connector module comprising a first mateable part of a wet mateable subsea electrical connector configured for releasable subsea mating engagement with a second mateable part at the end of an electrical ethernet cable; the media converter device having at least one optical input/output junction and at least one electrical input/output junction, and a bi-directional electrical/optical converter module connected between the input/output junctions and configured to convert optical input signals received at the optical input/ output junction into electrical output signals at the electrical input/output junction, and to convert electrical input signals received at the electrical input/output junction into optical output signals at the optical input/output junction; the optical input/output junction communicating with one or more optical fibers extending from a subsea optical or electro-optical cable connected to the first port of the subsea housing; one or more electrical conductors (35, 42) extending from the electrical input/output junction to the electrical cable connector module for communication with at least some of the electrical conductors of an electrical ethernet cable connected to the subsea electrical cable connector module; characterised in that the first chamber comprises a hermetically sealed, reinforced atmospheric chamber. a subsea housing containing at least a first chamber having a first port configured for connection to a subsea optical or electro-optical cable and a second, electrical input port; a media converter device mounted in the first chamber; a subsea electrical cable connector module connected to the second, electrical input port of the first chamber of the subsea housing and configured for releasable connection to an electrical ethernet cable, the subsea electrical cable connector module comprising a first mateable part of a wet mateable subsea electrical connector configured for releasable subsea mating engagement with a second mateable part at the end of an electrical ethernet cable; the media converter device having at least one optical input/output junction and at least one electrical input/output junction, and a bi-directional electrical/optical converter module connected between the input/output junctions and configured to convert optical input signals received at the optical input/ output junction into electrical output signals at the electrical input/output junction, and to convert electrical input signals received at the electrical input/output junction into optical output signals at the optical input/output junction; the optical input/output junction communicating with one or more optical fibers extending from a subsea optical or electro-optical cable connected to the first port of the subsea housing; one or more electrical conductors (35, 42) extending from the electrical input/output junction to the electrical cable connector module for communication with at least some of the electrical conductors of an electrical ethernet cable connected to the subsea electrical cable connector module; characterised in that the first chamber comprises a hermetically sealed, reinforced atmospheric chamber.