Abstract: A magnetometer having an enclosed cell containing He.sup.3 therein for receiving light from a light source, a light source for directing light to the enclosed cell along a predetermined path, a single pick-up coil containing therein the light source and the enclosed cell, a solenoid containing the pick-up coil therein and a data collection system coupled to the pick-up coil. The light source is a source of circularly polarized light and can comprise a He.sup.4 cell and an optical system and a circular polarizer disposed serially between He.sup.4 cell and enclosed cell containing He.sup.3. The predetermined path of the light source, the enclosed cell and the pick-up coil are disposed along the axis of the solenoid. The light source can also be a laser.

Abstract: A smart mine includes a pair of He.sup.3 magnetic sensors exteriorly connected to a head compartment of a mine housing. A torpedo compartment for housing a torpedo completes the mine housing. The head compartment contains the sensor support electronics which includes a phase locked loop means having a pair of digital phase locked loops connected between the sensors and a difference circuit whereby a difference signal representative of the difference between the pair of He.sup.3 magnetic sensors is produced for processing in a signal processor for determining the presence of large ferromagnetic bodies and producing a torpedo firing signal.