This paper proposes a passive localization algorithm that can locate sound sources underwater using a 4-element compact array. Through simulation, its performance is compared to that of a standard time difference of arrival algorithm. The algorithm is implemented in a real-time system on a System-on-Chip (Soc) which executes the algorithm. The resources and power requirements of the SoC are evaluated. This peripheral is integrated with a controller program running under the PetaLinux operating system. Finally, the performance of the implemented real-time system is compared to a MATLAB simulation, which demonstrates the potential for the remote platform to reliably detect marine mammals.