In many ingenious ways the chasers supplemented the work of other anti-submarine craft. Destroyers and other patrol boats kept track of the foe pretty well so long as he remained on the surface; the business of the chaser, we must remember, was to find him after he had submerged. The Commander-in-Chief on shore sometimes sent a radio that a German had appeared at an indicated spot, and disappeared beneath the waves; the chasers would then start for this location and begin hunting with their listeners. Aircraft which sighted submarines would send similar messages; convoys that had been attacked, individual ships that had been torpedoed, destroyers which had spotted their prey, only to lose track of it as soon as it submerged, would call upon the chasers to take up the battle where they had abandoned it. As long as the chasers operated in the waters which I have indicated, those between Start Point and Lizard Head, they "got" no submarine; the explanation was simple, for as soon as the chasers and British hunting vessels became active here, the Germans abandoned this field of operations. This was the reason that the operative area of the Plymouth detachment was extended. Some of the chasers were now sent around Land's End and up the north Cornish coast, where colliers bound from Wales to France were proving tempting bait for the U-boats; others operated farther out to sea, off the Scilly Islands and west of Brest. In these regions their contacts with the submarine were quite frequent.