At the Battle of Harpers Ferry on September 15, 1862, Tyler's division surrendered to the forces of Confederate Lieutenant General Thomas J. "Stonewall" Jackson. The Union soldiers, who were paroled after their capture, were sent to Camp Douglas, which already had been used as a prisoner of war camp for Confederates captured at the Battle of Fort Donelson, for temporary detention. Under the terms of the prisoner exchanged cartel then in effect, they had to await formal exchange before they could leave the camp. These 8,000 paroled Union soldiers began to arrive at Camp Douglas on September 28, 1862 and Tyler took temporary command of the camp. Under Tyler's command these Union soldiers had to live under similar conditions to those endured by the Confederate prisoners from Fort Donelson. In fact, the conditions were worse because the camp had become filthy and even more run down during its occupancy by the prisoners. The parolees had a two-month stay at the camp. Tyler was relieved as commander on November 20, 1862. Later, Tyler commanded at Baltimore, at Harper's Ferry between June 13, 1863 and July 3, 1864, and finally at the District of Delaware between July 3, 1863 and January 19, 1864.