When the Mexican War broke out, young Forney enlisted in the First Regiment of Alabama Volunteers, commanded by Colonel Coffey, in which command he became a lieutenant, serving as such at the siege of Vera Cruz. Returning home after the expiration of the term for which he enlisted, which was one year, he entered again on the study of his law books. Licensed to practice in 1848, he was the next year chosen a representative from Calhoun County to the legislature. With this single interruption he was devoted to his profession till the declaration of hostilities between the northern and southern states. He entered the army as a captain in the Tenth Alabama Regiment which was destined to suffer from unusual casualties from the first conflict in which it was engaged to the close of the war. The regiment of which he was a member was doing some detached duty at Drainville, Va., when it became engaged with the enemy, and among the seriously wounded was Captain Forney, who was shot in the leg, but within sixty days he was again in command of his company at the front. Meanwhile he had become the major of his regiment, with which he was engaged in the battle of Yorktown. At Williamsburg he was again shot, receiving a very serious wound in the shoulder which disabled his right arm. Removed to the buildings of William and Mary College, which were temporarily improvised as a hospital, Major Forney fell into the hands of the enemy and was detained as a prisoner for four months. On his return to his command after his imprisonment, he found himself at the head of his regiment by reason of logical promotion. He had the misfortune to receive another wound at the battle of Salem Church, though the injury was not of a serious nature. While leading his regiment at Gettysburg, he was again most seriously wounded, the arm wounded at Williamsburg, and even disabled, being now shattered. He fell on the field from the terrible shock, and while prostrate, he received another wound by a ball carrying away part of his heel bone. In this precarious condition, he fell into the hands of the enemy, and was retained a prisoner of war more than a year. While confined as a prisoner at Fort Delaware, he was among the fifty officers chosen to be exposed to the Confederate guns on Morris Island, and was taken near the scene ready for such exposure as a matter of retaliation, but humane and timely intervention checked the atrocious design, and in due time Colonel Forney was exchanged. Still a cripple and hobbling on crutches, he returned to his command in 1864, and was commissioned a brigadier general. Though seriously hampered by his maimed condition, he stolidly and heroically bore his misfortune, and led his brigade in the battles of Hatcher's Run, High Bridge, and Farmville. He steadfastly and doggedly clung to his command, rendering valiant and efficient service throughout the entire struggle, and was with his tattered veterans at Appomattox when General Lee surrendered.