Jeffers was born on October 16, 1824, in Swedesboro, New Jersey, the son of John Ellis Jeffers, a lawyer of Massachusetts birth, and Ruth, daughter of Amos Westcott of New Jersey. His eagerness for sea service was quickened by his maternal uncles, who were naval officers, and he secured a midshipman's appointment, September 25, 1840, and until 1845 served in the United States and Congress on the Pacific and Brazil stations.
Jeffers studied at the Naval Academy from October 10, 1845, to July 11, 1846, graduating fourth in a class of forty-seven.
In 1846, Jeffers published a book, The Armament of our Ships of War. In the steamer Vixen, during the Mexican War, he took part in all the important operations against shore defenses. Again at the Naval Academy as instructor, 1848-1849, he published two textbooks, Nautical Routine and Stowage; with Short Rules in Navigation (1849), in collaboration with J. M. Murphy, and A Concise Treatise on the Theory and Practice of Naval Gunnery (1850). In 1852-1853 and again in 1857 Jeffers was engaged in survey work in Honduras for a proposed "interoceanic railway, " and later, 1859-1860, as hydrographer in surveys for a canal route across the Chiriqui Isthmus. Meantime he was in the Brazil Squadron, 1853-1856, commanding the Water Witch in a survey expedition up the Parana and La Plata Rivers. The firing on this vessel by a Paraguayan battery led to the naval punitive expedition of 1857. On January 30, 1855, Jeffers had been made lieutenant. In the Civil War he commanded the steamer Philadelphia, April to May 1861, in the Potomac; then served in the Roanoke on the Atlantic blockade; and, commanding the gunboat Underwriter, took an active part in operations, January to February 1862, in the North Carolina sounds, receiving commendation for "zeal and intelligence. " His special studies in ordnance were doubtless partly responsible for his transfer to the command of the Monitor, March 13, 1862, just after her engagement with the Merrimac. In this vessel he participated in the bombardment of Drury's Bluff, May 15, and in other operations on the James River. His report on the Monitor gave a detailed and highly valuable study of the defects of her type and the remedies. Made lieutenant commander July 16, 1862, Jeffers was engaged in ordnance duty during the remainder of the war, first at Philadelphia, and after September 1863, as inspector and in charge of experiments at the Ordnance Yard, Washington. Among other activities he assisted in preparing the powder-ship Louisiana for explosion, December 24, 1864, off Fort Fisher. After eight years of routine duties, chiefly in sea command, he was chief of the bureau of ordnance, 1873-1881. In addition to books already mentioned, he edited Inspection and Proof of Cannon (1864), and Ordnance Instructions for the United States Navy (4th ed. , 1866, 5th ed. , 1880), and wrote Nautical Surveying (1871), and Care and Preservation of Ammunition (1874). Popular and uniformly courteous, he had a firm spirit, illustrated by his refusal to admit the suffering of his last illness. His death occurred in Washington on July 23, 1883, and he was buried in the Naval Cemetery, Annapolis, Maryland.
Jeffers was married, September 17, 1850, to Lucie LeGrand Smith, daughter of Surgeon S. B. Smith of the United States Army, by whom he had a son who died at seven, and a daughter.
