On the 11th the commodore started with his fleet for the Cumberland, protecting transports conveying six regiments of troops and the supplies for the entire force. On the same day McClernand, with the advance, moved out a few miles towards the point of attack. The next morning, Grant himself, with the main body of the army, consisting of fifteen thousand strong, marched from Fort Henry, leaving twenty-five hundred men in garrison there. The roads were inundated, and it was impossible to transport tents and baggage. But few wagons were taken, and the only food carried was in the haversacks of the soldiers. In order to understand the difficulties in the way of the gallant commander, it should be remembered that this movement was made in the month of February. The country was flooded with water, rendering the roads almost impassable, and requiring that many streams should be bridged. But without tents or baggage, the confident general moved on to do the mighty work before him. At noon he arrived at his destination, and proceeded to post his troops. Grant's information in regard to the fortress was so meagre and indefinite that he could only promise to issue the necessary orders in the field. This was the task now before him. Fort Donelson was one of the most elaborately constructed systems of works which yet frowned on the path of the Union army. It was built on a group of hills, the highest of which were not less than a hundred feet above the level of the river. It consisted of a nest of forts, thrown around the principal one, mounting, with the addition of the field guns of the batteries, sixty-five pieces. The country in which it was situated was rough, and densely wooded. The approaches to the works were rendered difficult by ingeniously-contrived abatis. Above and below the fort was a stream, overflowing its banks, and protecting the right and left of the rebel line. Water batteries on the river effectually guarded the approaches in that direction. The fort was garrisoned by twenty-one thousand men. For a week the rebels had been at work, day and night, increasing its defences, and calling in reënforcements from the vicinity. Grant went to work with his usual promptness, and before night had surrounded the fort, so far as the overflow of the streams would permit. McClernand's division was on the right, Smith's on the left. There were but three educated officers on the field--Grant, Smith, and McPherson; all the rest of the force were volunteers, most of whom had never seen a battle, and some had been in the service but a very brief period.