Admiral Mayo, in his capacity of commander-in-chief of our ships in European as well as home waters, made an official visit to Europe in September, 1917, inspecting bases and forces, and conferring with naval leaders of Great Britain, France and Italy. He was on duty again in Europe in 1918. Attending the Allied Naval Conference in London, he urged the construction of the North Sea Barrage, which was shortly afterwards approved. Visiting the famous Dover Patrol, he witnessed a bombardment of Ostend by British monitors, and had the experience of being under enemy fire. The flotilla leader _Broke_, in which he embarked with Sir John Jellicoe, First Sea Lord of the Admiralty, and other British officers of high rank, flew the flags of both Mayo and Jellicoe. The monitors, armed with 15-inch naval guns, were accompanied on these expeditions by spotting aircraft and destroyers. The party accompanied the _Terror_. Soon after she began to fire, the German shore batteries got the range. Firing with precision and accuracy, some of the German shells fell within a short distance of the _Broke_. Admiral Reginald Bacon gives this interesting account of the incident: On Tuesday, September 25th [1917], Sir John Jellicoe, Admiral Sir Henry Oliver, and Admiral Philpotts arrived at Dover and came with Admiral Mayo and his staff up the patrol line. It was a quaint experience for them. Half an hour after leaving Dunkirk in the _Broke_ we lost sight of the shore. After an hour's steaming we sighted the _Terror_ and destroyers in the open sea, and the motor-launches just starting their smoke-screen. Nothing else was in sight except a small monitor five miles away right out at sea, burning her searchlight for an aiming mark. Really our visitors must have thought we were humbugging when the _Terror_ opened fire and fired single rounds at fixed intervals. A few seconds afterwards while steaming about in the _Broke_--we had altered course three points--a splash came from a Tirpitz shell about 300 yards off. It fell very near the spot where we would have been if we had kept on our original course. I apologized to the American Chief of the Staff for not having kept on and brought the shell nearer. His reply was quaintly American in humor: "Don't mention it, Admiral; by the time we get to New York that shell will have been close alongside right enough!" The result of the _Terror's_ shooting was most successful, as all the rebuilding in the dockyard done by the Germans was again demolished. On October 19th, the _Terror_ was torpedoed, and had to be docked. On the following day the _Soult_ fired at Ostend and destroyed a high explosive magazine. One German craft was sunk, and two more damaged.