[1] Jackman joined the Norwich University faculty as Professor of Mathematics, Natural Philosophy, Civil Engineering and Military Science.

[4] In the 1830s and 1840s Jackman was part of a group of individuals interested in reorganizing and revitalizing the state militias, which had become increasingly dormant in the years following the War of 1812.

Ransom, and Frederic Williams Hopkins, held seminars to discuss tactics, strategy and recruiting, and carry out maneuvers and drills in an effort to improve unit readiness.

[9] Working in concert with Adjutant General Peter T. Washburn, Jackman devised a process for receiving recruits at a central location, equipping them and training them before sending them to the front lines.

[10][11] Following the Confederate Raid on St. Albans, Vermont in October, 1864, the northernmost action of the Civil War, General Jackman commanded troops along the Canada–US border.