It used to be a catchword of naval correspondents that "submarine cannot fight submarine." Well, it is true, and it isn't. What can be done is that one submarine submerged can torpedo another submarine on the surface: in which case submarine No. 2 is not really a submarine at the moment. Two submarines may meet and have a gun-action, with possible damage to one or both of them, and much entertainment to their crews; but in such a case neither boat would be acting as a submarine.
Throughout the war our boats have been on the look-out for, and ready to engage, any enemy submarines met with. We have had boats, in varying numbers, since the middle of 1915 engaged definitely in submarine-hunting--that is, those boats that could be spared from the all-important task of watching the Bight and its approaches. The anti-submarine boats we sent out simply proceeded to areas where, by inference or by "information received," U-boats might be expected to be working. The ordinary patrol boats on passage to and from their stations, or while watching at their stations for the coming of big ships, often met with U-boats, and naturally took the chances the gods gave them with gun, torpedo, stem, or whatever means seemed best at the moment.
Of course, the torpedo was the usual weapon used. A hit on a big ship, once the destroyer screen has been avoided, is comparatively easy; a hit on a U-boat is mighty difficult. The attacker is looking at his target with his eye (the top prism of the periscope) only a few inches above water-level. His view of the enemy, therefore, is confined to a square-looking conning-tower, with heavy "jumping wires" (sweep deflectors) running down from it to a low grey line of hull. It is therefore difficult to exactly estimate the enemy's speed or course, and the short time at the attacker's disposal for deciding on his deflection and turning to bring his tubes to bear does not allow of an accurate calculation based on bearings of the passing target. In fact, it is usually a case of "make up your mind and shoot quick." In addition to the handicap of the target being small, there is the knowledge that one must be far more careful to show only a little of the periscope during the attack, as submarines are far more on the _qui vive_ for periscopes than big ships are. For one thing, they know what a periscope looks like; and for another, they have more knowledge of what a torpedo can do against craft of small buoyancy.