An activation and operation mode system (1) for an electrochemical battery for the propulsion of marine craft, in particular for torpedoes; the system being equipped with an inlet valve (8) for the inflow of water from the outside environment, a flow rate regulator (11) of the flow input through the inlet valve (8), an outlet valve (9) for the outflow of the liquids and gases produced by the chemical reaction, and a mode valve (16) movable from a discharge position, in which the fluid produced by the chemical reaction is conveyed to the outlet valve (9), and a recirculation position, in which said fluid is made to recirculate through the electrochemical cells of the battery; the inlet valve (8), the outlet valve (9), the flow rate regulator (11) and the mode valve (16) being grouped in a single external body (17) so as to define a compact monolithic assembly.