Milford Haven, Liverpool, and other ports were more often used for this purpose. Vessels had been arriving here for several days from ports of the Irish Sea and the east coast of England. These had now been formed into convoy "O Q 17"; they were ready for a destroyer escort to take them through the submarine zone and start them on the westward voyage to American ports.
This escort consisted of eight American destroyers and one British "special service ship"; the latter was one of that famous company of decoy vessels, or "mystery ships," which, though to all outward appearances unprotected merchantmen, really carried concealed armament of sufficient power to destroy any submarine that came within range. This special service ship, the Aubrietia, was hardly a member of the protective escort. Her mission was to sail about thirty miles ahead of the convoy; when observed from the periscope or the conning-tower of a submarine, the Aubrietia seemed to be merely a helpless merchantman sailing alone, and as such she presented a particularly tempting target to the U-boat. But her real purpose in life was to be torpedoed. After landing its missile in a vessel's side, the submarine usually remained submerged for a period, while the crew of its victim was getting off in boats; it then came to the surface, and the men prepared to board the disabled ship and search her for valuables and delicacies, particularly for information which would assist them in their campaign, such as secret codes, sailing instructions, and the like. The mystery ship had been preparing for this moment, and as soon as the submarine broke water, the gun ports of the disguised merchantman dropped, and her hitherto concealed guns began blazing away at the German. By October, 1917, these special service ships had already accounted for several submarines; and it had now become a frequent practice to attach one or more to a convoy, either ahead, where she might dispose of the submarine lying in wait for the approaching aggregation, or in the rear, where a U-boat might easily mistake her for one of those stragglers which were an almost inevitable part of every convoy.
Trawlers and mine-sweepers, as was the invariable custom, spent several hours sweeping the Queenstown Channel before the sailing of convoy "O Q 17" and its escort. Promptly at the appointed time the eight American ships
