Grant wrote a letter to the War Department at Washington tendering his services, and saying:  “I feel myself competent to command a regiment, if the President in his judgment should see fit to intrust one to me.”  For some reason, never explained, this letter remained unanswered, though the department was then and afterward in constant need of educated and experienced officers.  A few weeks later, however, Governor Yates commissioned him colonel of one of the Illinois three years’ regiments.  From that time until the end of 1861, Grant, by constant and specially meritorious service, rose in rank to brigadier-general and to the command of the important post of Cairo, Illinois, having meanwhile, on November 7, won the battle of Belmont on the Missouri shore opposite Columbus.

The “demonstration’” ordered by Halleck was probably intended only as a passing show of activity; but it was executed by Grant, though under strict orders to “avoid a battle,” with a degree of promptness and earnestness that drew after it momentous consequences.  He pushed a strong reconnaissance by eight thousand men within a mile or two of Columbus, and sent three gunboats up the Tennessee River, which drew the fire of Fort Henry.  The results of the combined expedition convinced Grant that a real movement in that direction was practicable, and he hastened to St. Louis to lay his plan personally before Halleck.  At first that general would scarcely listen to it; but, returning to Cairo, Grant urged it again and again, and the rapidly changing military conditions soon caused Halleck to realize its importance.

Within a few days, several items of interesting information reached Halleck:  that General Thomas, in eastern Kentucky, had won a victory over the rebel General Zollicoffer, capturing his fortified camp on Cumberland River, annihilating his army of over ten regiments, and fully exposing Cumberland Gap; that the Confederates were about to throw strong reinforcements into Columbus; that seven formidable Union ironclad river gunboats were ready for service; and that a rise of fourteen feet had taken place in the Tennessee River, greatly weakening the rebel batteries on that stream and the Cumberland.  The advantages on the one hand, and the dangers on the other, which these reports indicated, moved Halleck to a sudden decision.  When Grant, on January 28, telegraphed him:  “With permission, I will take Fort Henry on the Tennessee, and establish and hold a large camp there,” Halleck responded on the thirtieth:  “Make your preparations to take and hold Fort Henry.”

It would appear that Grant’s preparations were already quite complete when he received written instructions by mail on February 1, for on the next day he started fifteen thousand men on transports, and on February 4 himself followed with seven gunboats under command of Commodore Foote.  Two days later, Grant had the satisfaction of sending a double message in return:  “Fort Henry is ours....  I shall take and destroy Fort Donelson on the eighth.”