From “Fort Henry and Fort Donelson“:
Shortly after the surrender of Fort Sumter, Confederates built two forts just south of the border of Tennessee and Kentucky. … Fort Henry guarded the Tennessee River while Fort Donelson guarded the Cumberland. … The key to rolling up the Confederate defense of the Mississippi River was the capture of Fort Henry and Donelson. That job fell to General Ulysses S. Grant and Commodore Andrew Foote. …
Fort Henry was easy prey for the Union gunboats … When Fort Henry surrendered, Grant turned his attention to Fort Donalson. … Inside Fort Donelson, General John Floyd commanded, with Gideon Pillow and Simon Bolivar Buckner under him. …
Gideon Pillow launched an assault against the Union right (McClernand), demolished 5 brigades in the federal line, forcing them into full retreat and grabbed a road that led to Nashville. Pillow had a number of good choices he could have made: turn left or right to battle the exposed flanks of Grant’s army, or use the road he had captured to evacuate to Nashville. Pillow, generally regarded as the worst general on either side during the Civil War, decided to withdraw back into the fort because his men seemed exhausted.
… That evening, Floyd, Pillow and Buckner considered surrender. Buckner, lowest ranking of the three generals, was the one left to do the task. Buckner and Pillow slipped out by boat and Nathan Bedford Forrest, his cavalry and a few foot soldiers found a partially flooded land route out minutes before it was closed off by Union infantry.
According to General Grant’s memoirs, one of Grant’s first questions to Buckner was: “Where is Pillow? Why didn’t he stay to surrender his command?”
Buckner: “He thought you were too anxious to capture him personally.”
Grant: “Why if I had captured him I would have turned him loose. I would rather have him in command of you fellows than as a prisoner.”