The said cable is composed of several wires, each of which is insulated from the others. One of these wires is connected with the mechanism for starting and stopping the boat, one is connected with the steering apparatus, one serves for indicating to the operator at all times the exact position of the rudder, one is connected with mechanism for elevating and depressing the said guide rods, and one serves for firing the charge in the magazine. The motive power for effecting the necessary movements of the mechanism or apparatus in performing the above operations is obtained from the aforesaid engines, which are provided with suitable valves arranged in combination with electro magnets, shunts, and the devices connected with the said wires of the cable, as hereinafter set forth. This form of cable has since been replaced by one which consists of two wires only, the one for performing all of the necessary operations, exclusive of the firing or exploding of the magazine, and the other exclusively for this latter purpose. This improvement is effected by employing a series of relays or resistance coils, or a multiple, or compound relay in the boat. The advantages gained by this improved form of cable are:-- 1.--Increased flexibility. 2.--A greater length of cable may be coiled in a given space. 3.--A thicker coat of insulating material may be used, thereby more perfectly insulating it. 4.--It is much cheaper. Two rudders are generally used, one below and one above the boat, as shown at _U_, Fig. 122. These rudders are operated and controlled by means of a small auxiliary engine _T_, Fig. 122, which is started, stopped, and reversed by the electric current conducted through the cable _Q_ in connection with magnets attached directly to a valve forming part of the said engine. This valve is so actuated by the magnets that when the current passes in one direction the engine _T_ will move the rudder to starboard, and when the current acts in the opposite direction it will turn the rudder to port. The mechanism for firing the charge in the magazine _A_^{1} is clearly shown in Fig. 124, and operates as follows:--Projecting from the front extremity or stem of the boat is a rod or pin _V_, which extends through a suitable packing box _W_ into the said magazine or charge chamber; when the boat strikes an object, the said rod is forced inward into contact with the springs or points _X_, thereby closing an electrical circuit and igniting a cartridge, shown at _Y_, in the magazine.