Current autonomous underwater vehicles generally use multibeam sonars and Doppler velocity logs to aid their inertial navigation systems. While effective, these active acoustic systems can reveal the presence of a vehicle, making them unsuitable for covert operations. This report presents the key findings from a research project investigating the feasibility of using a quantum magnetometer array as a substitute or complement to active sonar sensors in autonomous underwater vehicles. Field and sea trials demonstrate that the magnetic field near the Earth’s surface exhibits significant spatial variations, enabling speed estimation and absolute positioning using quantum magnetometer arrays. Theoretical analysis shows that temporal variations in the Earth’s magnetic field, rather than sensor noise, set the fundamental performance limit for estimating vehicle speed using a magnetometer sensor array. However, if a continuous forward communication link with a rate of ∼ 10 bits/s is available, the temporal variation can, to a large extent, be removed by transmission of correction data. Temporal variations also make map-matching-based positioning challenging. But by estimating the magnetic-field gradient using a magnetometer array, temporal variations can be effectively canceled, making gradient-based magnetic-field map-matching a promising approach. Further work is needed to quantify the effects of platform-induced disturbances and map imperfections.