Our submarine campaign in the Sea of Marmora must also have a separate chapter to itself, not only because it is now a closed episode in the history of the War, but because it was conducted under quite unique conditions. The scene of operations was not merely distant from the submarine base, it was divided from it by an approach of unusual danger and difficulty. The channel of the Dardanelles is narrow and winding, with a strong tide perpetually racing down it, and setting strongly into the several bays. It was moreover protected, as will appear in the course of the narrative, by forts with powerful guns and searchlights and torpedo tubes, and by barrages of thick wire and netting it was also patrolled constantly by armed ships. Yet from the very first all these defences were evaded or broken through with marvellous courage and ingenuity; for nearly a year a succession of brilliant commanders took their boats regularly up and down the passage, and made the transport of Turkish troops and munitions across the Marmora first hazardous, and finally impracticable. Their losses were small; but they passed the weeks of their incredibly long patrols in continual danger, and snatched their successes from the midst of a swarm of vigilant enemies. Two battle-ships, a destroyer, and five gunboats fell to them, besides over thirty steamers, many of which were armed, nine transports, seven ammunition and store ships, and no less than 188 sailing-ships and dhows with supplies. The pages which follow contain notes on the cruise of every British boat which attempted the passage of the Straits; but they are far from giving an account of all their amazing feats and adventures. Lieutenant Norman Holbrook had the honour of being the first officer to take a British submarine up the Dardanelles. He carefully prepared his boat--B. 11--for the business of jumping over and under obstacles, by devices which have since been perfected but were then experimental. The preliminary trials turned out very satisfactorily, and on Sunday, December 13, 1914, as soon as the mainland searchlights were extinguished at dawn, he trimmed and dived for Seddul Bahr.