LAIDLEY, Theodore Thaddeus Sobieski, soldier, born in Guyandotte, Virginia, 14 April, 1822; died in Palatka, Florida, 4 April, 1886. He was graduated at the United States military academy in 1842, and was appointed 2d lieutenant in the ordnance corps. From 1842 till 1846 he served as assistant in various arsenals, and then in the war with Mexico, where he participated in the siege of Vera Cruz, battle of Cerro Gordo, and the siege of Pueblo. Just before the battle of Cerro Gordo, Lieutenant Laidley and Lieutenant Roswell S. Ripley were charged with the placing of an eight-inch howitzer on the summit of a hill on the south side of the Rio del Plan in such a manner as to enfilade the enemy's line of batteries from the right. The work was accomplished at night, over an almost impracticable route that was obstructed by rocks and tropical shrubbery. The gun was placed, and in the morning an effective fire was at once opened, and the enemy driven out of his works. The appearance of a gun of such calibre, with sufficient supports, in such a place, discouraged the Mexicans, and their forces surrendered. Laidley received the brevets of captain and major, and at the close of the war returned to Watervliet arsenal as assistant ordnance officer. Subsequently for ten years he was engaged on ordnance duty at various stations, becoming captain in July, 1856. In 1858 he was assigned the duty of compiling a new ordnance manual, which became known as the "Ordnance Manual of 1861" and remained a standard for many years. During the civil war he was inspector of powder in 1861-'2, and then was in command of Frankford arsenal until 1864, when he became inspector of ordnance, and was given charge of the Springfield armory until 1866. Afterward he had command of the New York arsenal on Governor's island, and later of that at Watertown, N. g., becoming colonel in April, 1875. He served on several boards for making scientific tests and experiments, and was president of the commission to test the strength and value of all kinds of iron, steel, and other metals at the Watertown arsenal in 1875-'81. Colonel Laidley was retired, at his own request, in December, 1882, after over forty years of active service, being at the time of his retirement senior colonel in the ordnance department. He invented several valuable appliances that are now used in the department, including an igniter, a laboratory forge, an artillery forge, and a cavalry forge. Besides important government reports, he was the author of "Instructions in Rifle Practice" (Philadelphia, 1879).