The arrangement for adjusting the length of range and for drawing and replacing the wedge is as follows: Two cog-wheels, a large one and a small one, are fixed on the upper part of the after-end of the torpedo, just in front of the propellers. The small wheel has thirty teeth, gearing in an endless screw attached to the propeller-shaft, and of such a pitch that one revolution of the propeller moves the wheel one tooth. The big cog-wheel is so arranged as to move one tooth for each revolution of the small wheel. In front of this gearing is a small stud that works fore and aft in a slot, being provided with a spring which tends to force it towards the after-end of the slot. This stud is connected by a rod to the valve which admits the compressed air to the cylinders of the engine. When the stud is in the forward part of the slot the valve is open, in the after part it is closed. By means of a lever the spring of the stud is compressed, and the stud is moved to the fore part of its slot; the big wheel is then moved around until a stud on its face is the desired number of teeth above the lever. Now for every thirty revolutions of the propeller, or one tooth of the big wheel, a certain known distance is travelled, varying according to the pattern of the torpedo, slip, etc. When the propeller has made the number of revolutions corresponding to the desired length of range, the stud on the big wheel presses against the lever of the spring and releases the latter, forcing the valve-rod back and closing the valve. Attached to the axle of the big wheel is a small brass arm which is connected by means of a brass rod to the safety-wedge, and is so arranged that after any required number of revolutions of the propeller the safety-wedge will be drawn out; or it may be drawn out at the instant of discharge. By means of an additional lever at the fore port of the torpedo, which is connected by means of a rod to the valve of the engine, and by arranging the attachment of the safety-wedge to the brass rod from the big wheel so that on the wedge being withdrawn it is released from the brass rod, the action of the closing of the valve after the run of the torpedo is completed, forces the wedge into its securing position again. Naturally the torpedo would float at the end of its run from its difference of buoyancy, owing to the compressed air used in working the engines.