In this thesis a simple and low-cost aided inertial navigation system is presented which can be used to automate underwater search operations. The system is designed and implemented to be compatible with a VideoRay Pro 3 tethered mini-ROV. Inertial-, compass- and pressure measurements are collected with a dedicated embedded system and transferred to the surface for processing. System states are estimated, compared against a user specified pattern and used to generate path-following control inputs. The system is tested on a small scale and the results obtained through camera-based measurements show acceptable performance for short time intervals.