Abstract: An underwater location beacon emits a continuous wave signal which is phase-shift modulated by a pseudo-noise, spread spectrum code. This signal is detected with an exact replica of the transmitted code. To an unauthorized observer without the replica, the transponder's signal is indistinguishable from background ocean noise. The spread spectrum code allows extraction of the signal from high levels of ocean noise, providing an increased detection range, jamming resistance, covertness, and unique signals for each pinger. The outputs of the surface spread spectrum receiver are used with automated location algorithms. Several receivers at different surface positions provide the underwater coordinates of the pinger's location.