After first briefly reviewing current techniques for detecting submarines, we focus on the Weakness in Magnetic Anomaly Detection technique. Our group has proposed a new approach for reducing measurement noise by studying the relationship between fluctuations in the total electron content (TEC) in the ionosphere and variations of the geomagnetic field (H) measured on the ground. We have set up two tri-axial magnetometers and a GPS-based TEC register system, all of which have been recording continuously since 2001. Preliminary results are presented for correlations between fluctuations in TEC and H, obtained by statistical and dynamical spectrum analysis using the wavelet method in ultra-low-frequency bands. These results support the theory that it is magnetohydrodynamic waves, originating in the magnetosphere and propagating downward through the ionosphere as electromagnetic waves, that cause fluctuations in both geomagnetic field and TEC. I will also discuss the polarization characteristics of the geomagnetic field - the main precursors of earthquakes - which have the potential to distinguish whether the source of a disturbance is from space or from a submarine.