A submarine may be any kind of surface vessel, with the advantage added to her of being able to dive. She need not necessarily be a diving boat with a few torpedo tubes and a couple of guns. She may be anything. A surface ship can only be one thing; you cannot have a cruiser-monitor or a destroyer-battleship. But a submarine may be two things at once; and a submarine can, as a result, act unsupported. Take the case of a scouting submarine. What is the alternative? If we had no scouting submarines we would have had to keep a ring of destroyers out to watch the Bight. Those destroyers might, being out near the enemy's coast, be attacked by enemy cruisers, so that it would be essential to keep our cruisers out in support. Then if the enemy brought out--and so on--up to the final result of our battle fleet being continuously at sea, which would have been not only unnecessary wear and tear on the big ships, but a good opportunity for the U-boats if they had cared to take a chance. Take the case of the submarine mine-layer. She has the great advantage, to begin with, of not only getting to her position unseen, but of being able to lay her unpleasant cargo down unsuspected and unobserved. Then, again, she does not need a supporting force to follow her in case she meets with trouble. She does not look on a big enemy ship as a trouble, should one interfere with her; she would rather describe the big ship as a "gift." She is open to the usual anti-submarine methods, and can be dealt with by destroyers, seaplanes, and so on; but if she succumbs to their attacks--well, that is another submarine gone, but it might have been a big surface ship. By the nature of the German strategy our lines of design were indicated. The chief type we needed were scouts--in other words, patrol boats. We built these in considerable numbers, for the several types of patrol boats we diverged into were capable of doing any of several things. They could do the Heligoland Bight patrol, attacking the enemy if met with, and reporting to the C.-in-C. what they saw on their patrols; they could go out into the Atlantic to hunt U-boats on the traffic lanes, or they could go to the Mediterranean to work in the Adriatic. They were the general-utility craft of the Submarine Navy. The mine-layers were of the patrol boat type, getting larger as the War went on, but always with the torpedo-tubes (reduced in number) built into them to allow them to become normal submarines when a chance arose.