Cairo, Illinois, at the confluence of the Ohio and the Mississippi Rivers, was vital to the United States because of its location and the operations base established there. The Mississippi Flotilla had nine new ironclad gunboats, seven of which were the creation of James B. Eads, a boat builder in St. Louis. Each of the seven had 13 guns, a flat bottom, and shallow draft. Protection was provided by a sloping casemate covered with iron armor 2.5 inches thick designed by Samuel Pook. The most famous of "Pook's Poodles" was the USS Carondelet.

The first test of three of these new warships was against Fort Henry, an earthen fort that the Confederates had hastily constructed on the east (Tennessee) bank of the Tennessee River during the winter of 1861-62. When Confederate Brig. Gen. Lloyd Tilghman was sent to command the fort, he immediately realized that Fort Henry was indefensible, because it was constructed on low ground susceptible to flooding and was directly across the river from high ground. In January 1862 he ordered the construction of a new fort on the high ground on the west (Kentucky) side of the Tennessee River, known as Fort Heiman. The new fort remained under construction when Union Brig. Gen. Ulysses S. Grant launched his offensive against Forts Henry and Donelson in early February 1862.

In a joint army-navy operation a fleet of seven gunboats - four ironclads and three wooden ones -- under Union naval Flag Officer Andrew H. Foote steamed out of Cairo, Illinois, on February 2, leading the transports carrying Grant's force. On February 4-5, Grant landed his divisions in two different locations, one on the east bank of the Tennessee River to prevent the garrison at Fort Henry from escaping and the other to occupy the high ground on the Kentucky side to ensure the fall of both Forts Heiman and Henry. After Foote's gunboats began bombarding the forts, Tilghman recalled the troops building Fort Heiman to assist in the defense of Fort Henry. Tilghman soon realized that he could not hold Fort Henry. Thus, he ordered his barbette-mounted cannons to hold off the Union fleet while he sent most of his men to Fort Donelson, 11 miles away.

On February 6, the Union gunboats steamed to within 200 yards of Fort Henry and knocked out 13 of its 17 heavy guns. Confederate fire exploded the boiler of the Essex, a converted ironclad, causing 38 casualties. Tilghman surrendered both forts Henry and Heiman after 70 minutes of bombardment, enabling the Federals' wooden gunboats to ascend the Tennessee River south to Muscle Shoals, Alabama.

After the fall of Fort Donelson on the Cumberland River, ten days later, the two major water transportation routes in the Confederate west, bounded by the Appalachians on the east and the Mississippi River on the west, became Union highways for movement of troops and material.

In 1993, the Civil War Sites Advisory Commisision designated the Battle of Fort Henry as one of the Civil War's 384 principal battlefields. The Battle of Fort Henry, along with the battle at its sister Forts Heiman and Donelson, is nationally significant, because it was the first great Union victory of the Civil War, and it gave the North a new military hero - "Unconditional Surrender" Grant - who was promoted to major general. After the Confederate surrender of these three forts, the South was forced to give up southern Kentucky and much of Middle and West Tennessee, and the Tennessee and Cumberland rivers became avenues for Union penetration into the heartland of the Deep South. Thus, Fort Henry, along with its sister forts, was a major battle that had a direct, observable impact on the Federal quest to obtain control of the principal rivers in the western Confederacy and hence the outcome of the Vicksburg campaign, as well as a decisive battle that had a direct, observable impact on the direction, duration, and final outcome of the Civil War.

Fort Henry would continue to be managed by the U. S. Forest Service as a part of the Land Between the Lakes National Recreation Area. Cooperative agreements between the National Park Service at Fort Donelson National Battlefield and the U. S. Forest Service at the Land Between the Lakes National Recreation Area would be explored to govern any mutual advantageous approaches to the preservation and interpretation of the historic resources of Forts Henry, Heiman, and Donelson.