By mid-1915 the British submarines loose in the Sea of Marmara were causing the Turkish authorities a great deal of concern. An official German assessment of the British submarine menace stated;
The activity of hostile submarines was a constant and heavy anxiety. They dislocated very seriously the conveyance of reinforcements to the Dardanelles and caused many disagreeable losses. If communications by sea had been completely severed, the Turkish Army would have been faced with catastrophe.
[Quoted in Tom Frame, The Shores of Gallipoli: Naval Dimensions of the Anzac Campaign, Sydney, 2000, p.212]
This photograph shows something of the effect of the British submarine campaign on voyages in the Sea of Marmara in 1915. Turkish soldiers line the rails of a steamer on the lookout for submarines. Journalist Granville Fortescue, in whose book the image appears, described a passage on a steamer from Istanbul to the Turkish town of Gallipoli (Gelibolu):
Hardly had we passed the powder works than twelve Turkish soldiers, carrying their rifles at the ready, filed up from the hold to take station along the starboard and port rails. With the muzzles of their guns pointing over the waters, they strain their eyes searching for any sign of a dreaded submarine … to the excited mind of these soldiers, every porpoise is a periscope, and every sleeping duck a danger. Time and time again they fire into the flood, the crack of their rifles tending to quiet their apprehensions. Though I search for hours through my glasses, I could see nothing that would warrant this waste of ammunition.
[Granville Fortescue, Russia, the Balkans and the Dardanelles, London, 1915, pp.216-217]