The records of young Pike's earliest military service are variant in some particulars not of much consequence. In one of his letters, printed beyond, p. lxv, he says that he entered the army when he was 15 years old. This would be in or about 1794, and doubtless refers to his cadetship. According to his biographer, he entered his father's company as a cadet, date not given; was commissioned as an ensign of the 2d Infantry Mar. 3d, 1799; promoted to be a first lieutenant in the same regiment Apr. 24th, 1800, and arranged to the 1st Infantry in 1802. In Heitman's Historical Register[M-4] it appears that Zebulon Montgomery Pike, of New Jersey, was first appointed from New Jersey to be a second lieutenant of the 2d Infantry, Mar. 3d, 1799; was next promoted to be first lieutenant of the same regiment, Nov. 1st, 1799; and then transferred to the 1st Infantry, Apr. 1st, 1802. Whatever may have been the facts in the discrepant cases of the earlier dates, there is no uncertainty from April 1st, 1802, when the name and rank became First Lieutenant Z. M. Pike, 1st Regiment of U. S. Infantry. It was as such that this young officer was first detailed for detached service in the exploration of the Mississippi, by order of General James Wilkinson, dated from the Commanding General's headquarters at St. Louis, Mo., July 30th, 1805.
Pike had not before been distinguished from any other meritorious and zealous subaltern, though his qualities had already attracted favorable attention. His selection by General Wilkinson for this duty was the beginning of all his greatness. The letter in which the detail was made will be found elsewhere (vol. ii, pp. 842-844). The principal other dates of Pike's brief but brilliant military career may be conveniently given here, though in so doing I anticipate events which will come up again in their regular order: His promotion to a captaincy in his regiment occurred by routine Aug. 12th, 1806, when he was voyaging up the Osage, early in his second expedition. He became major of the 6th Infantry May 3d, 1808, in less than a year after his return from his tour in Mexico--a journey which was directly continuous with his second, or Arkansaw expedition, but one which, having been involuntarily performed, he chose to separate formally from the other, and to make known as his "third" expedition. He became the lieutenant-colonel of the 4th Infantry Dec. 31st, 1809. From Apr. 3d, 1812, to July 3d of that year, he was on duty as deputy quartermaster-general. He became the colonel of the 15th Infantry July 6th, 1812, and was appointed to be brigadier-general Mar. 12th, 1813. But before this appointment was confirmed General Pike had been killed at the head of the troops he led to the assault on York, Upper Canada, April 27th, 1813, aged 34 years, 3 months, 22 days.