then served as director of the Sappers, Miners and Pontoniers at West Point. Cullum published the forerunner of his Biographical Register in 1850. He took two years leave of absence from 1850 to 1852 for health reasons, and traveled throughout Europe, Asia, Africa and the West Indies while recuperating. Cullum then returned to West Point, and taught there until 1855. When Robert E. Lee, at the time superintendent of West Point, went on a vacation to Virginia, Cullum served as acting superintendent of the Academy from 5 July to 27 August 1853. In 1848, he introduced a type of bridge pontoon, which was used in the Mexican–American War. Cullum published Description of a System of Military Bridges, With India-Rubber Pontons in 1849. Civil War and later military service On 9 April 1861, Cullum was promoted to the rank of lieutenant colonel, and shortly after to colonel. He served as an aide-de-camp to General Winfield Scott from 1 April 1861 to 1 November 1861. At the same time he was a member of the United States Sanitary Commission. Cullum was promoted to a Major in the Corps of Engineers, before becoming chief engineer of the Department of the Missouri on 19 November 1861, where he remained until 11 March 1862. Cullum then was chief engineer for the Department of the Mississippi until 11 July. During the time, he was also the chief of staff for Henry Halleck. He was appointed brigadier general of volunteers on 1 November 1861. From 2 December 1861 to 6 February 1862, Cullum was on the board that inspected the defenses of St. Louis and the board that inspected the condition of the Mississippi Gun and Mortar Boat Flotilla. He travelled to Cairo, Illinois, where he commanded operations auxiliary to various armies in the field and also managed the defense of the District of Cairo. From February to March, he surveyed the Confederate defenses at Columbus, Kentucky. On 6 February 1862, the Union Army under then Brigadier General Ulysses S. Grant captured Fort Henry, and ten days later, on 16 February, they captured Fort Donelson. With these victories, his forces took about 12,000 to 15,000 Confederate prisoners. The army was unprepared to handle this many prisoners and scrambled to find places to house them. Cullum sent many prisoners to St. Louis before he received War Department instructions to direct 7,000 prisoners to Camp Douglas near Chicago. Cullum