The policy of defence adopted was that of making the line of the Canal the line of resistance. A large portion of the low-lying desert to the north-east of the Canal was flooded, so as to render approach by that direction impossible. Warships took up stations in the Canal itself, while naval patrol launches took over the duty of guarding the Bitter Lakes. The troops detailed for the defence of the Canal itself were entrenched upon the western side, with reserves concentrated at points of tactical importance. In this way full advantage was taken of the lateral communications on the western side of the Canal, while it was thought that the difficulties of crossing the desert on the eastern side would make approach by the Turks well-nigh impossible. Meanwhile, the Turk was not letting the grass grow under his feet. Whether the Germans ever intended to pay the price for Turkish adhesion by sending a strong enough force to make the invasion of Egypt practicable is open to doubt. The Turkish rank and file were certainly led to believe that a serious invasion of Egypt was intended. But it is much more likely that the object of the Germans was to detain as large a British force as possible in Egypt and thus prevent their taking part in the fighting in France. A secondary object may have been to render the Suez Canal temporarily impassable. Whatever may have been the chestnuts that Germany hoped to get out of the fire, it was clear that Turkey was willing to act as catspaw, and attempt a foolhardy invasion of Egypt. Consequently, the construction of a new military railway in Syria was put in hand, and by January, 1915, the Turks had formed advanced posts at Auja, on the frontier, and also at Kosseima, El Arish, and Khan Epenus in the desert. The problem of water supply has always presented a difficulty to armies crossing this waterless desert. There are a certain number of reservoirs and cisterns which hold up water during the rains. In the winter time these would be full. The Turk is less particular about the water which he drinks than the white man, and doubtless he could, to some extent, be supplied from some of the brackish pools in the desert, with water that no one would think of offering to a British soldier. The light pontoons that the Turks dragged across the desert for crossing the Canal are said to have been used for carrying water during certain stages of the advance. Suffice it to say that the Turks did succeed in solving the water problem, and in crossing the desert with a force of some considerable strength.