After capturing Fort Henry on February 6, 1862, Brig. Gen. Ulysses S. Grant advanced cross-country to invest Fort Donelson. On February 16, 1862, after the failure of their all-out attack aimed at breaking through Grant's investment lines, the fort's 12,000-man garrison surrendered unconditionally. This was a major victory for Brig. Gen. Ulysses S. Grant and a catastrophe for the South. It ensured that Kentucky would stay in the Union and opened up Tennessee for a Northern advance along the Tennessee and Cumberland rivers. Grant received a promotion to major general for his victory and attained stature in the Western Theater, earning the nom de guerre "Unconditional Surrender."