When _Speculation_ had gone about 2½ miles on her way, the Chief Skipper suddenly heard her fire a shot; and the same moment she changed course and blew her siren. _Lark_ and _Lysander_ raced to join the hunt with their utmost speed. They found _Speculation_ cruising round, with depth-charges ready to drop. She had already dropped two, besides firing her 3-pounder into the wake of the enemy’s periscope, and had seen not only oil, but some wreckage, and a large object which rolled over and disappeared again. The Chief Skipper ordered her to proceed on her course to St. Ives, and then instructed _Lysander III_ to stand by and drop her depth-charges on the chance of stirring up the wounded U-boat. Within five minutes he sighted the wake of a submarine on his own port bow, only 100 yards distant but going fast. He made a bee line for the wake, thinking it possible he might ram her, and when just over the disturbance on the water he dropped his first depth-charge. Then, as the submarine was still making headway, he closed again and dropped his second charge right over the wake. The enemy thereupon showed oil and ceased to make headway; so _Lark_ and _Lysander_ alternately bombed his supposed resting-place with no less than eight charges. After nearly an hour of this, they stood by, listening on hydrophones and watching the oil still rising. Then a destroyer arrived, asked questions, heard the whole story and steamed away without comment. Two hours later a motor-launch came by, and was good enough to examine the spot and contribute one more depth-charge. Two hours more, and _Speculation_ returned to spend the night with her division--all listening keenly, but without result. Finally, next morning, two sweepers, _John Kidd_ and _Castor II_, arrived and swept round about the buoy which had been put down. The three boats of the division stood by and watched anxiously; they felt sure that the sweep fouled some object between 9 and 10 A.M., but at 11.15 they received the order to resume their patrol and went reluctantly away, foreboding a verdict of ‘probably damaged.’