the discipline of the whole convoy system rested upon the theory that the submarine was there, waiting only the favourable moment to start the work of destruction. But a submarine, as already said, could not strike without the most thorough preparation. It must get within three or four hundred yards or the torpedo would stand little chance of hitting the mark in a vital spot. The commander almost never shot blindly into the convoy, on the chance of hitting some ship; he carefully selected his victim; his calculation had to include its speed, the speed of his own boat and that of his torpedo; above all, he had to be sure of the direction in which his intended quarry was steaming; and in this calculation the direction of the merchantman formed perhaps the most important element. But if the ships were constantly changing their direction, it is apparent that the submarine could make no calculations which would have much practical value. In the afternoon the _Aubrietia_, the British mystery ship which was sailing thirty miles ahead of the convoy, reported that she had sighted a submarine. Two or three destroyers dashed for the indicated area, searched it thoroughly, found no traces of the hidden boat, and returned to the convoy. The next morning six British destroyers and one cruiser arrived from Devonport. Up to this time the convoy had been following the great "trunk line" which led into the Channel, but it had now reached the point where the convoys split up, part going to English ports and part to French. These British destroyers had come to take over the twenty ships which were bound for their own country, while the American destroyers were assigned to escort the rest to Brest. The following conversation--typical of those that were constantly filling the air in that area--now took place between the American flagship and the British: _Conyngham_ to _Achates_: This is the _Conyngham_, Commander Johnson. I would like to keep the convoy together until this evening. I will work under your orders until I leave with convoy for Brest. _Achates_ to _Conyngham_: Please make your own arrangements for taking French convoy with you to-night. _Achates_ to _Conyngham_: What time do you propose leaving with French convoy to-night? _Conyngham_ to _Achates_: About 5 P.M. in order to arrive in Brest to-night. Devonport Commander-in-chief to _Conyngham_: Proceed in execution Admiralty orders _Achates_ having relieved you. Submarine activity in Lat. 48.41, Long. 4.51. The _Aubrietia_ had already given warning of the danger referred to in the last words of this final message. It had been flashing the news in this way: 1.15 P.M. _Aubrietia_ to _Conyngham_: Submarine sighted 49.30 N 6.8 W. Sighted submarine on surface. Speed is not enough. Course south-west by south magnetic.