With a force of 3,100 men General Grant made an incursion into Missouri to break up a rebel camp at Belmont, where he fought his first battle in the Rebellion. He had accomplished his purpose, when the enemy was reinforced from Columbus, on the other side of the river, and though he brought off his command in safety he narrowly escaped capture himself. Fremont was superseded by Halleck, and for the next two months Grant was employed in organizing and drilling troops. Columbus, with 140 cannon and full of men and material, closed the Mississippi. The Confederate line of defence against the invasion of the South extended from this point across the country, including Fort Henry on the Tennessee and Fort Donelson on the Cumberland, the latter mounting forty guns, with quarters for 20,000 soldiers. Grant was studying this line of defence, devising a plan to break through it. By order of General Halleck he had sent out a reconnoissance in force, under General Smith, who reported to him that the capture of Fort Henry was practicable. Grant forwarded this report to the commander of the department, and asked for permission to attack it. This was refused in sharp and curt terms. A written application, earnestly seconded by Commodore Foote, who had brought the gunboat service up to a state of efficiency in the West, secured the desired order. With 17,000 men, in connection with 7 gunboats under the command of the commodore, Grant started upon his mission the day after he received the order. Fort Henry was captured, though the army was not engaged. The main body of the Confederate force escaped to Fort Donelson. The capture of Fort Henry cheered the army and the people. Grant telegraphed the result of the attack to Halleck, and announced his intention to proceed against Fort Donelson. Leaving 2,500 men to garrison the fort, Grant marched with 15,000 from Fort Henry, while a considerable addition to his force came up the river. The fortification was invested, and after three days of persistent fighting in cold, snow, and hunger, the fort surrendered. The gunboats were severely handled by the water batteries of the enemy, and the commodore was badly wounded, so that most of the work fell upon the army. It was a brilliant victory, and the loyal nation resounded with the praises of Grant. This was the pointer to the fame he afterward achieved. His reply to the rebel general, "I propose to move immediately on your works," was repeated all over the country, and the initials of his name came to mean "Unconditional Surrender," the terms he had demanded of the commander of the fort.