A system for power and data transmission in a body of water to unmanned underwater vehicles comprises a floating surface station (3) for generating electric energy and receiving and transmitting data; an underwater station (2) connectable to at least one unmanned underwater vehicle (4); at least one submerged depth buoy (8; 23; 26); and an umbilical (5), which comprises a power transmission line and a data transmission line, is mechanically and electrically connected to the surface station (3) and to the underwater station (2), and is mechanically coupled to the depth buoy (8; 23; 26) so that the umbilical (5) comprises a first umbilical section (9) that is stretched between the underwater station (2) and the depth buoy (8; 23; 26) and a second umbilical section (10) that extends loose between the depth buoy (8; 23; 26) and the surface station (3).