and protective resins in a second embodiment not shown it is envisaged that the linear motor may also be of the variable reluctance type in this case the fixed part of the motor integral with the guide is made of ferromagnetic material instead of conductive material although described with a fixed and movable component arranged along a single pair of opposite sides of the fixed guide 10 and the tube 20 it is envisaged that a similar structure may be realized on the other pair of opposite sides of the said guide and tube obtaining in this way two complementary motors able to increase the overall force exerted on the tube for movement thereof fig4 shows a variation of embodiment of the apparatus according to the invention in which the plates 143 integral with the moving tube 20 and containing the windings are arranged asymmetrically in the longitudinal direction of movement of the said tube with such an arrangement it is possible to obtain a further result consisting in the fact that the force of magnetic attraction which is produced between the winding 143 integral with the tube 20 and fixed part 42 integral with the guide 10 exerts forces in the opposite direction to those produced by the hydrodynamic thrust of the water on the slides 21 of the tube 20 when the submarine is moving.