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