When it is desired to sink, the vessel is set in motion in the awash position, from which it is gradually steered downwards by the diving rudders, until only the periscope, or it may be not even that, is left showing above. Then the maximum of water is being displaced. It is then actually displacing more than its own weight of water, for if left to itself it will rise rapidly and it is only the speed and the action of the rudders which keep it under. We see, then, that the action of a submarine in submerging itself is a real genuine dive. It sinks upon an even keel until it is awash, after which it goes under "head-first," just as a swimmer does. It also rises bow first. This tendency to rise when the combined action of movement and rudder ceases constitutes a very considerable safeguard, for should anything happen to the propelling machinery the vessel simply rises. At one time weights were attached to the under side of the hull which could be detached from the inside so that in the event of the vessel descending against the wish of her commander, she could be simply forced to the surface by the great excess of buoyancy resulting from shedding these "safety weights." Of course, in the event of a serious perforation of the hull neither of these forms of surplus buoyancy would bring the boat up. Let us now trace the operations of diving right through, supposing that our submarine is first running light. In that condition she is being driven by the oil engines which constitute her primary propelling power. The hatch or door at the top of the conning-tower is open, as also, it may be, is the one lower down, just at the foot of the tower. Men are standing upon the little platform formed by the tower, and one of them is steering by means of a wheel, keeping his eye, moreover, upon a compass also provided there, that being in fact, to the submarine when light, what the bridge is to the ordinary steamer. Other members of the crew may be upon the superstructure or deck just below, while others again are down inside, attending to their duties there. Under these conditions the inside is by no means an unpleasant place. Plenty of fresh air comes down through the open hatches and through the ventilators, it being drawn down through the latter by means of a fan. Preparations are then made for submerging. The hand-rail along the little deck is removed. The upper steering wheel and compass are covered up or shut away into the coverings provided for them, the wireless apparatus, if provided, is removed and the mast shut down. Hatches are securely closed and valves in the ventilating pipes are closed. In fact every opening is shut and made water-tight so that no risk shall be run of diving prematurely and taking in water accidentally.