Shortly after the fall of Fort Donelson, McClernand commented on how, "I have from the breaking out of the rebellion attentively and carefully studied the immediate valley of the Mississippi as a principal field of military operations."
In September, when Grant was showing little interest in taking Vicksburg, McClernand was expressing how, “I would carry the war into their heart, not only for the purpose of crushing the rebellion itself, but as the quickest and surest way to reopen the Mississippi River. Indeed the reopening of the river is one of the first steps I would take in subduing the rebellion.” He detailed his strategy to Lincoln "Both in a military and commercial aspect this step is eminently important. It is important in a military view, first, because it would afford the means of cheap and easy communication between our troops disposed at different points on the Mississippi River and its navigable tributaries, and because it would facilitate the concentration of them at any one or more of those points; secondly, because it would cheapen the cost of supplying our men and animals at or near New Orleans with provisions and forage. It would do that by subsisting the overflowing granaries of the Northwest for the remoter sources of such supplies in the East, and thirdly, because, in securing to us the command of the Mississippi River, it would enable us to stop the communication between the revolted States and their armies east and west of that river, thus isolating each section as to the other, destroying the unity of their plans and combination, and cutting off the rebel forces of the river from their wonted source of supplies in Texas." He went on with other strategic advice to Lincoln.
On October 15, 1862 McClernand recommended a well balanced force of 24,000 infantry, 3,000 cavalry, 400 sappers, 1000 sharpshooters, and both 1500 light and 100 heavy artillery, but also delineates the various numbers and types of artillery to take, totaling 30,000 men and 60 cannon of various types and 12 siege train guns (30 #ers and mortars). In early December, McClernand looked to mount one-fifth of the infantry.
On November 15th, McClernand had already concluded that an effective operational plan against Vicksburg would be crossing the river below the city: “The way cleared from New Orleans to Vicksburg, it would be expedient that transports, under convoy of gunboats, should be sent up the Mississippi to a point as near Vicksburg as might be found safe to meet the contingency of a determination to cross our troops over the river below it, after having disembarked them above and marched them around.” It took Grant up until the following April to reach that same conclusion (even though he claimed an earlier date in his Memoirs).