[1] In 1847, during the War with Mexico, the President of the United States requested that a regiment of Maine infantry be mobilized for field duty.

However, this partial mobilization and the influence of the Crimean War of 1853–56 excited military enthusiasm in Maine, and caused new militia companies to be organized in 1854–56.

[2] Abraham Lincoln's first call for volunteers in April, 1861 required Maine to raise one regiment of infantry for three months of Federal service.

This was done by reorganizing ten existing companies of the state militia, completed at Portland, Maine on 28 April 1861 and mustered into service on 3 May 1861, a total of 779 soldiers.

The regiment was mustered into the service of the United States at Augusta, Maine on 26 May 1898, with 46 officers and 979 enlisted men.

Dana T. Merrill, a brigadier general in the United States Army, began his career by enlisting in Company H in 1898.