This would be accomplished preferably by the co-operation of two boats. They would take opposite sides in the channel, with a connecting rope extending out through the diving compartment. It is obvious that as they move along the rope will sweep the whole mine-field and gather in the connecting cables. This would be indicated at once to the operators in the diving compartment by the load upon the sweeping line. A grapple may then be attached to the rope and sent out of one boat and hauled into the other, and thus drag the mine so near that a diver could go out and destroy its electrical connections or cut it adrift. Should the latter operation be the aim, the grapple may be so fashioned as to accomplish this without the diver leaving the compartment. This latter method is one strongly recommended by some of the most prominent military authorities on submarine defense.] [Illustration: This picture indicates the manner in which the boats have traveled many miles over all kinds of bottom. In the present instance the boat is shown systematically searching the bottom with her diving door open and strong lights being used to facilitate a more perfect examination. There is no trim or equilibrium to maintain. When the propelling machinery stops the boat comes to rest. A cyclometer attached to these wheels gives a fairly reliable reading of the distance traveled under normal circumstances. As the currents do not carry her out of her course, and as her gauges give an absolute record of changing depths, it is possible to so navigate upon the bottom with remarkable precision. In shallow waters this method has many advantages.] [Illustration: A MACHINE WHICH MAKES THE DIVER’S TASK EASY SHOWING TUBE HANDLING CARGO IN SUNKEN SHIP.] Recovering Cargo or Submerged Objects Without the Aid of Divers.