On a calm, frosty morning some three weeks later the boats of the old night guard, now doing their spell of day duty, discovered a long trail of thick greenish-black oil on the surface leading seawards. It was evident that a hostile submarine had rested during the previous night on the sandy bottom in the shallow water close inshore and, rising to the surface, had made off at daybreak. The trail was followed and information was quickly received from an Iceland trawler, which had passed the submarine on the surface some two hours previous. Ships were concentrated by wireless, and although it did not fall to the lot of the M.L.'s to give the _coup de grace_, they had the satisfaction of returning to harbour with the knowledge that their honour had been retrieved, and yet another German submarine would never again commit outrage on the high seas. CHAPTER XVIII THE CASUALTY THERE were duties performed by the new navy which bore no relationship to anti-submarine fighting, or, in fact, to warfare at all, unless it was to the ceaseless battle waged between all who go down to the sea in ships and the elements they seek to master. One such as this occurred at a little northern seaport in the late winter of 1917, unimportant and scarcely worth relating except as an illustration of the diverse services rendered by men of this great force during the years of national peril. * * * * * The gale was at the height of its fury when the March day drew to a close. The whole east coast of Scotland, from John o' Groats to the mouth of the Tweed, was a study in black and white--the white of foam and the black of rocks. All the minesweepers and smaller patrol ships had been confined to their respective bases for several days, and in a certain small harbour many of the officers and crews of the imprisoned ships were spending their time ashore, in the warmth and cheery comfort of hospitable firesides. The boisterous day became a wild night. The wind howled and whistled over the barren moors and through the streets of the small fishing town. Houses trembled and chimneys rocked under the blasts. Although a watch on the signal tower and elsewhere was religiously maintained, it was of little value, as all that could be seen in the darkness to seawards was a hazy mist of flying spray which the wind whisked from the surface and carried several miles inland. Standing back from the sea, and some half-mile from the centre of the little fishing town, stood a substantially built house, more commodious and better furnished than many of its neighbours, which had providentially fallen into the temporary grasp of one of the married officers of the patrol flotilla, who generously kept open house for his less fortunate brothers-in-arms.