The prime difficulty of the operation was the want of water. The Khalifa's position was nearly 125 miles from the river. The intervening country is, in the wet season, dotted with shallow lakes, but by January these are reduced to mud puddles and only occasional pools remain. All the water needed by the men, horses, and mules of the column must therefore be carried. The camels must go thirsty until one of the rare pools--the likely places for which were known to the native guides--might be found. Now, the capacity of a camel for endurance without drinking is famous; but it has its limits. If he start having filled himself with water, he can march for five days without refreshment. If he then have another long drink, he can continue for five days more. But this strains his power to the extreme; he suffers acutely during the journey, and probably dies at its end. In war, however, the miseries of animals cannot be considered; their capacity for work alone concerns the commander. It was thought that, partly by the water carried in skins, partly by the drying-up pools, and partly by the camel's power of endurance, it might be just possible for a force of about 1,200 men to strike out 125 miles into the desert, to have three days to do their business in, and to come back to the Nile. This operation, which has been called the Shirkela Reconnaissance, occupied the Kordofan Field Force. The report of the route from Kohi was considered encouraging. At Gedid the old wells promised sufficient water to refill the skins, and within seven miles of the wells were two large pools at which the camels could be watered. The column, therefore, prepared for the journey. Nothing was neglected which could increase the water carried or diminish the number of drinkers. Only twelve cavalry were taken. The horses of the Maxim guns and the mules of the battery were reduced to the lowest possible number. Every person, animal, or thing not vitally necessary was remorselessly excluded. In order to lighten the loads and make room for more water, even the ammunition was limited to 100 rounds per rifle. The daily consumption of water was restricted to one pint for men, six gallons for horses, and five for mules. To lessen the thirst caused by the heat Colonel Kitchener decided to march by night. An advanced depot was formed at Gedid and food for two days accumulated there. Besides this, each unit carried ten, and the column transport seven, days' rations. Thus the force were supplied with food up till the 9th of February, and their radius of action, except as restricted by water, was nineteen days. This was further extended five days by the arrangement of a convoy which was to set out on the 30th of January to meet them as they returned.