"Well," said Mark Redisham, "I'm not certain; but I suppose she's looking for mines. They're not floating right on the surface, you know. They're held just about a foot below low water level, so that when a vessel passes she'll go bang on to them. But the pilot up there can see them, as a gannet sees a fish, and I expect he'll drop a signal when he spots one."
For something like an hour the seaplane searched, followed by the gunboat, with the trawlers moving in pairs in her wake.
When at length a signal was sent down that mines had been sighted, "dans," or small buoys with flags attached, were put out to mark the spot from which operations were to begin. Each couple of trawlers got ready their dredge tackle, dropping over the stern a long wire rope, heavily weighted. The weight drawn by each boat was connected with that of its partner by a yet longer wire hawser, weighted to keep it submerged and stretched below the level of the floating mines. The two vessels, ranging themselves on either side of the mine-field, steamed ahead on a parallel course, so that their submerged gear should catch upon the mooring-lines and sweep up the mines floating between them.
This process was carried on simultaneously by the other trawlers, clearing a wide lane through the mine-field, while the gunboat and the seaplane continued their searching for new fields.
When the mines were thus caught and brought to the surface, they were exploded from a safe distance by gunfire. You may be sure there were many narrow escapes from serious accident.
During the first afternoon, the Dainty and her working partner, the Ripple, brought up two mines together. They came into violent contact with each other, exploding so close astern of the Ripple that she was caught in the edge of the upheaval and badly damaged. Her crew made for the boat, thinking that all was over with them; but her skipper controlled them, and himself crawled below into the narrow space near the screw shaft, discovered the damage, and stopped the leak sufficiently to enable the pumps to keep the water down and save the ship.
Within a quarter of an hour of this accident, one of the other trawlers struck a mine and was shattered to fragments.
At the end of two days, the field having been cleared, the gunboat returned to port. Shortly after she had gone, Mark Redisham and his companions watched a squadron of British dreadnoughts and cruisers steaming safely across the area from which the danger had been so industriously removed.
Their trails of smoke had hardly faded from the horizon when Mark, still looking in the direction in which they had disappeared, noticed a curious disturbance in the calm water, about a couple of miles away.
At first he thought it was a school of gambolling porpoises showing their fins, but presently the periscopes and conning-tower of a submarine rose to the surface. The conning-tower was marked "U15," and he knew by this that she was German.