“I’m sorry, sir,” returned Edwards.

“So am I,” returned his commander.  “We’ll have to catch that fellow, and it is likely to prove a hard job.  However, the sooner we get after him the better.”

“And what do you intend to do, sir?” asked Jack.

“We’ll take another of these vessels and put to sea again,” declared his commander.  “We may come up with him sooner than we expect.  But—­we’ll take a British crew this time.”

It was now after daylight and Lord Hastings set about his preparations with vigor.  Before evening the lads found themselves aboard one of the German submarines that had been captured and brought to the surface.  The vessel was manned with a full complement of British underwater sailors.  Edwards was among them.

“We’ll go down the river immediately,” said Lord Hastings, after a tour of inspection of the vessel, “and when we are at sea we’ll fly the German flag.  None of our submarines looks anything like this craft, so if we come up with the enemy we will be taken for a German.  You may steam at ten knots, Mr. Templeton.”

Jack gave the order and the vessel moved down the river.

Shortly after nightfall the submarine, U-6, was proceeding into the North Sea, for it was there that Lord Hastings believed he would be more likely to encounter Davis and the U-16.

“Besides,” he explained, “our usefulness is not at an end in the matter of obtaining information from the Germans.  We may put into Ostend again if necessary.”

All during the night, although Frank, Jack or Lord Hastings was continually on the bridge, they did not encounter anything that looked like an enemy ship, although the U-6 dived several times when it drew close to a British ship of war—­one of the blockading fleet Had the submarine approached too closely it would have drawn a shot from the battleship, whose commander could not possibly have known that the German submersible carried a British crew in the service of King George.

The following afternoon, having traveled far toward the east, they were to have an adventure.

Moving slowly along, and presenting the appearance, from a distance, of a little speck upon the surface of the sea, the U-6 continued toward the east.  Frank had taken the bridge half an hour before and now was studying a faint smudge on the eastern horizon.  A moment later and a second smudge appeared and then a third, to be followed almost immediately by a fourth.

“Strange!” he muttered.  “Seems to be coming from the direction of Heligoland.  Battleships all right, but the question is, British or German?  Must be the latter, though how they figure to run the British blockade is more than I know.  However, I haven’t heard that any of our vessels are this close to Heligoland.  It’s too dangerous on account of the German mines.”

He summoned Jack, who also gazed curiously at the smoke for some moments; but even while Jack gazed, the dim outline of a large battleship came into sight.  Soon a second appeared and then a third.