[3] In 1861, Bennett enlisted as a Corporal in Co. E of the 36th Illinois Volunteer Infantry Regiment, a three-year unit known as the “Fox River Regiment.” Military authorities took advantage of his skills, assigning him to engineering duties at Rolla and St. Louis, Missouri throughout late 1861 and early 1862.

His detached duty, which included map-making and work on fortifications, ended in time for Bennett to join his regiment for the Battle of Pea Ridge, Arkansas on March 7, 1862.

Bennett was given the position of chief engineering officer of Colonel Nelson D. Cole's right, or eastern column of the expedition, which operated from July 1 to October 4, 1865.

As the chief engineering officer, he worked to build roads and bridges along the route that could accommodate the columns' 140 wagons and pack train.

At Dry Creek, Bennett rode with groups of dismounted soldiers deployed in skirmish lines, which made him a conspicuous target.

He continued to work as an engineer and surveyor, platting additions to the City of Springfield, and surveying railroad lines in Missouri and Oklahoma.