United States. Commissioned a major of engineers in July 1838, he was appointed superintendent of the Military Academy after the fire of 1838 and served till 1845. He designed the new buildings and the new cadet uniform that first displayed the castle insignia. He superintended the construction of coast defenses for New York Harbor from 1846 to 1855. In the beginning of 1855, Delafield was appointed by the Secretary of War, Jefferson Davis a head of the board of officers, later called The Delafield Commission, and sent to Europe to study the European military. The board included Captain George B. McClellan and Major Alfred Mordecai. They inspected the state of the military in Great Britain, Germany, the Austrian Empire, France, Belgium, and Russia, and served as military observers during the Crimean War. After his return in April 1856, Delafield submitted a report which was later published as a book by Congress, Report on the Art of War in Europe in 1854, 1855, and 1856. The book was suppressed during the American Civil War due to fears that it would be instructive to Confederate engineers as it contained multiple drawings and descriptions of military fortifications. Delafield served as superintendent of the Military Academy again in 1856–1861. In January 1861, he was succeeded by Captain Pierre G. T. Beauregard, who was dismissed shortly after Beauregard's home state of Louisiana seceded from the Union, and Delafield returned as superintendent serving until March 1, 1861. In the beginning of the Civil War he advised the governor of New York Edwin D. Morgan during the volunteer force creation. Then, in 1861–1864, he was put in charge of New York Harbor defenses, including Governors Island and Fort at Sandy Hook. On May 19, 1864, he was commissioned a brigadier-general after replacing Joseph Gilbert Totten, who had died, as the Chief of Engineers, United States Army Corps of Engineers, on April 22, 1864. He stayed in charge of the Bureau of Engineers of the War Department until his retirement on August 8, 1866. On March 8, 1866, President Andrew Johnson nominated Delafield for appointment to the grade of brevet major general in the Regular Army of the United States, to rank from March 13, 1865, and the United States Senate confirmed the appointment on May 4, 1866, and reconfirmed it due to a technicality on July 14, 1866. Later life After retirement Delafield served as a regent