sentences:  When the submarine submerged as "Patriot" approached and engaged with gunfire, the balloon directed "Patriot" in a depth charge attack against the submarine, which resulted in a small amount of oil coming to the surface, followed about an hour later by an apparent underwater explosion and a large slick of oil, which was believed to mark the sinking of the .In October 1917, "Patriot" formed part of a large-scale operation, involving 30 cruisers and 54 destroyers deployed in eight groups across the North Sea in an attempt to stop a suspected sortie by German naval forces.Despite these countermeasures, the two German light cruisers and , managed to evade the patrols and attacked the regular convoy between Norway and Britain, sinking nine merchant ships and two destroyers, and before returning safely to Germany.