But the overtures of Nuri and Gaafer proved too much for the loosely organized tribesmen of the Senussi, and ultimately for the Grand Senussi himself. The Egyptian littoral as far as the Tripoli frontier was sparsely populated, consisting only of a few coastguard stations and the strip of flat land between the Libyan plateau and the sea. The Khedival highway, a rough unmacadamized road cut as a relief work during famine, ran to Sollum on the border, and a railway ran west from Alexandria to Dabaa. It was only at the north end that the frontier had to be guarded, where were many little oases linked up by caravan-tracks, for to the south lay the impassable wastes of the Libyan desert. The possibility of trouble was suspected in May 1915, but it was not till August that the first hostile incident took place, when two British submarines, sheltering from bad weather on the Tripoli coast, were treacherously fired upon by Arabs, under a white officer. In the first week of November the crews of the _Tara_ and the _Moorina_, torpedoed by enemy submarines, landed in Cyrenaica, and were taken captive by the Senussi. On the 6th of that month, the little port of Sollum was shelled by U-boats, and an Egyptian coastguard cruiser sunk. After that Sollum and Sidi Barrani were subjected to repeated attacks by land, and it became necessary to admit a state of war. [Sidenote: _Dec. 25, 1915._] The frontier posts were drawn in to Mersa Matruh, which, with a railway eighty miles distant and the sea at its door, was well-equipped as a base to defend the marches. On 11th December Major-General Wallace, in command of the hastily-collected Western Frontier Force, moved out from Mersa Matruh and drove the enemy from the Wadi Senaab. On the 13th his column dispersed with considerable losses some 1,200 Arabs near Beit Hussein. Towards the end of the month an enemy force of some 5,000, under Gaafer, concentrated eight miles south-west of Matruh, and on Christmas Day General Wallace marched against it with two columns, one composed of English Yeomanry and Australian Light Horse, and the other of the 15th Sikhs, a battalion of the New Zealand Rifle Brigade, and a territorial battalion of the Middlesex. The action was of the familiar type—a frontal attack by the infantry, and a wide circling movement by the horse, and it resulted in a substantial check to the enemy. He lost nearly 500 killed and prisoners, and most of his transport and supplies, and the Grand Senussi and his staff retired to Unjeila and Bir Tunis. But the enemy was checked and not routed, and early in January 1916 he reappeared in force some twenty-five miles south-west of Matruh. It was clear that to safeguard the frontier he must be driven westward out of Egyptian soil and south into the desert, and General Wallace had not at his command the troops for such an operation. It was at this time that the South African Brigade arrived in Alexandria.