Disclosed is an underwater craft having an electrochemical battery activated by an electrolyte, including: an electrochemical cell; a tank (13) intended to contain the electrolyte; a seawater flow rate regulator (37) arranged upstream of the tank (13). The flow rate regulator includes: a fixed housing (60) including first ports (64); a slide (62) including second ports (66); the slide (62) being movable, in relation to the fixed housing (60), under the effect of the pressure of the seawater entering the regulator (37), to a balanced position in which the first and second ports (64, 66) define outlet openings (70) for seawater to flow to the tank (13), the slide (62) being movable between a maximum opening position, in which the area of the openings is at a maximum, and a maximum restriction position, in which the area of the openings (70) is at a minimum.