One of the things that made the work of the destroyer such a thankless task was that only in the rarest cases was it possible to prove that she had destroyed the submarine. Only the actual capture of the enemy ship or some of its crew furnished irrefutable proof that the action had been successful. The appearance of oil on the surface after a depth charge attack was not necessarily convincing, for the submarine early learned the trick of pumping overboard a little oil after such an experience; in this way it hoped to persuade its pursuer that it had been sunk and thus induce it to abandon the chase. Even the appearance of wreckage, such as arose on the surface after this _Conyngham_ attack, did not absolutely prove that the submarine had been destroyed. Yet, as this submarine was never heard of again, there is little doubt that Commander Johnson's depth charge performed its allotted task. The judgment of the British Government, which awarded him the C.M.G. for his achievement, may be accepted as final. The Admiralty citation for this decoration reads as follows: "At 5.50 P.M. H.M.S. _Orama_ was torpedoed in convoy. _Conyngham_ went full speed, circled bow of _Orama_, saw submarine between lines of convoy, passed right over it so that it was plainly visible and dropped depth charge. Prompt and correct action of Commander Johnson saved more ships from being torpedoed and probably destroyed the submarine." One of the greatest difficulties of convoy commanders, especially during the first months the system was in operation, was with "slacker" merchantmen; these were vessels which, for various reasons, fell behind the convoy, a tempting bait for the submarine. At this time certain of the merchant captains manifested an incurable obstinacy; they affected to regard the U-boats with contempt, and insisted rather on taking chances instead of playing the game. In such cases a destroyer would often have to leave the main division, go back several miles, and attempt to prod the straggler into joining the convoy, much as a shepherd dog attempts to force the laggard sheep to keep within the flock. In some cases, when the merchantman proved particularly obdurate, the destroyer would slyly drop a depth charge, near enough to give the backward vessel a considerable shaking up without doing her any injury; usually such a shock caused the merchantman to start full speed ahead to rejoin her convoy, firmly believing that a submarine was giving chase. In certain instances the merchantman fell behind the convoy because the machinery had broken down or because she had suffered other accidents. The submarines would follow for days in the track of convoys, looking for a straggler of this kind, just as a shark will follow a vessel in the hope that something will be thrown overboard; and for this reason one destroyer at least was often detached from the escorting division as a rear guard. In this connection we must keep in mind that at no time