An ice fishing submarine for carrying an end portion of a fishing line radially away from an ice fishing hole comprising: i) a hull enclosing a propulsion system which includes a battery which powers an electric motor which turns a propeller; ii) a power switch to begin propulsion away from the ice hole; and, iii) a tether having an unfixed end secured to the submarine and configured to interrupt power to the propulsion system when the tether becomes taut. When the submarine travels the distance of the length of the tether radially away from the ice hole the tether then becomes taut thereby automatically switching power off to the propulsion system of the submarine, and thereby eliminating the necessity of running control wires extending down through the ice hole to the submarine and monitoring the travel of the submarine to turn off power at an appropriate time.