As soon as the line as far as Kosheh was completed, the advance towards Dongola began. After the army had been victorious at Hafir the whole province was cleared of Dervishes, and the Egyptian forces pushed on to Merawi. Here they were dependent on river transport. But the Nile was falling rapidly, and the army were soon in danger of being stranded by the interruption of river traffic between the Third Cataract and Kenna. The extension of the line from Kosheh to Kerma was therefore of vital importance. The survey was at once undertaken, and a suitable route was chosen through the newly acquired and unmapped territory. Of the ninety-five miles of extended track, fifty-six were through the desert, and the constructors here gained the experience which was afterwards of value on the great Desert Railway from Wady Halfa to the Atbara. Battalions of troops were distributed along the line and ordered to begin to make the embankments. Track-laying commenced south of Kosheh on the 9th of October, and the whole work was carried forward with feverish energy. As it progressed, and before it was completed, the reach of the river from the Third Cataract to Kenna ceased to be navigable. The army were now dependent for their existence on the partly finished railway, from the head of which supplies were conveyed by an elaborate system of camel transport. Every week the line grew, Railhead moved forward, and the strain upon the pack animals diminished. But the problem of feeding the field army without interfering with the railway construction was one of extraordinary intricacy and difficulty. The carrying capacity of the line was strictly limited. The worn-out engines frequently broke down. On many occasions only three were in working order, and the other five undergoing 'heavy repairs' which might secure them another short span of usefulness. Three times the construction had to be suspended to allow the army to be revictualled. Every difficulty was, however, overcome. By the beginning of May the line to Kenna was finished, and the whole of the Railway Battalion, its subalterns and its director, turned their attention to a greater enterprise.