At noon on February 6, 1862, Union Flag Officer Andrew H. Foote's flotilla of four ironclad and three timberclad gunboats steamed upriver and began firing into Fort Henry in the opening battle of Brig. Gen. Ulysses S. Grant's campaign to open the Tennessee and Cumberland rivers to Union forces, and the first combat use of American ironclad vessels. Fort Henry, a hastily constructed earthen fort, was partially inundated by Tennessee River floodwaters and sat at or below water level, leaving its cannons unable to fire down onto the ironclads' vulnerable decks as those at Fort Donelson could. Knowing the fort could not be held, Brig. Gen. Lloyd Tilghman kept 100 artillerymen and sent about 2,500 other troops to Fort Donelson, 12 miles away on the Cumberland River. Tilghman and his gunners returned fire but were severely outgunned, and at 1:45 p.m., with only four cannon still operating, Tilghman surrendered to Foote. The Confederates lost 5 killed and 11 wounded, while Union sailors lost 11 killed and 31 wounded. Grant and Brig. Gen. John A McClernand's troops arrived only after the fort had been surrendered. The original site of Fort Henry now lies completely submerged beneath Kentucky Lake.