Immediately war was declared on Turkey several of our submarines were sent to the Dardanelles, to destroy, if possible, some of the Turkish warships. Submarine B11 was most successful in this work, and its commander, Lieutenant Norman Douglas Holbrook, R.N., was awarded the Victoria Cross for a conspicuous act of bravery on 13th December. On that day he entered the Dardanelles, and, notwithstanding the difficult current, dived his vessel under five rows of mines, and then torpedoed the Turkish battleship _Messudiyeh_, which was guarding the mine-field. After this exploit he brought his vessel back safely, though it was fiercely attacked by gun fire and torpedo boats. So beset was he that on one occasion he had to submerge the submarine for nine hours. [Footnote 178: See map on next page.] CHAPTER XXXIII. THE BATTLE OF THE SERBIAN RIDGES. During some hundreds of pages I have told you nothing about the part which gallant little Serbia was playing in the great struggle. On page 76 of our second volume I briefly summed up the situation at the end of August 1914. At that time the first Austrian invasion had failed, and the country was almost clear of the enemy. The Austrians had suffered a serious set-back. Early in September they prepared a second army of invasion. Before I follow its fortunes, I want you to look closely at the little map on the opposite page. You notice that from the railway uniting the Lower Drina with Shabatz on the Save, right away to the southern frontier, the country is criss-crossed in all directions by great uplands, almost as difficult for an army to traverse as those of Georgia. The river valleys alone give access to the interior, and afford railway routes. There are a few good government highways, but most of the roads are mere tracks, which in wet weather become quagmires. When once the autumn rains set in, the work of transport in Serbia is greatly hampered. All the lowland parts of Serbia lie along the right bank of the Save and the Danube. This district is open, though hilly. East of Shabatz the lowlands form a rough triangle, with the course of the river Save as its base, and the highland town of Valjevo, on the river Kolubara, as its apex. It was across this triangle of easy country that the Austrians made their second invasion. The Serbians did not wait for the Austrian attack, but pushed over the plain, and in the darkness of night on 6th September crossed the Save at several points, and made a dash on the Hungarian town of Semlin, opposite Belgrade. They occupied the place on the 10th, but were unable to hold it, and were driven back with heavy losses into the Tser Mountains, which you see marked on the map.