For no apparent reason whatever the engines would slow down and entirely stop, and in that position they would remain for ten, fifteen, twenty minutes or even half an hour, and then start up again on another tack. "I believe we've become separated from our convoy," said Slim, who had been upon deck, and now entered the wireless room where Joe and Jerry were watching Lieutenant Mackinson make some readjustments of the wireless mechanism. "The pilot doesn't seem to know the course. Say, wouldn't it be great sport if we should be lost from the others? But I wonder why the captain does not wireless them?" "No need," Lieutenant Mackinson assured him, "for we are not lost, nor are we separated from them. Every vessel in this fleet is simply carrying out a program secretly arranged long in advance, and which was in the nature of a sealed order which the various captains did not open until this morning. "I dare say that our convoy is as near us now as at any time during the voyage, and that it is maintaining the same position at all times, going through the exact maneuvers that the _Everett_ is performing." "It is to fool the submarines?" asked Joe. "Exactly," the lieutenant replied. "Our government is taking every precaution, and no unnecessary risks. You see, there is no way of keeping absolutely secret the departure of our transports. Nor is there any assurance that the information does not go directly to the German authorities, and from them to the commanders of the submarines. Our actions are designed to prevent them from estimating our course or position. "It was their knowledge of that fact, and their determination to learn our whereabouts in another way, which doubtless led to that spy being aboard this transport. I feel----" Suddenly the lieutenant ceased speaking, and all four, as of one accord, sprang toward the radio instruments. "Listen!" Lieutenant Mackinson commanded, as he jammed the headpiece over his ears. "SOS"--the most tragic of all the calls of the sea, was coming to them as a frantic appeal sent out through the air to any and all who might hear and respond. "SOS," the lieutenant wrote down hurriedly as the message came through space. And then: "American--_Memphis_--submarine pursuing--53-1/2 lat.--17 W. lon.--running fifteen knots three points south of west." The entire message was repeated, and then there was silence--the dense and seemingly impenetrable silence that had existed before. Came the nearer and more powerful crackle of the radio. "One of our destroyers is replying," Lieutenant Mackinson announced, and one by one he jotted down the words: "Continue same direction. U. S. destroyer be with you in about two hours." "Understand you," the return message came back a moment later. "Submarine still on stern. Has fired two shots, but both missed."