The Somerville Light Infantry was incorporated in 1853, as strife with the South suggested eventual warfare. Local militias were descendants of the colonial militias of earlier times. George Brastow, later the first mayor of the City of Somerville, was the Captain of the SLI when Lincoln called for men. He volunteered and returned home at the end of his tour of duty.
The SLI were also known as the Somerville Light Artillery. When the local militias were combined into the state militia, the SLI were reformed as Company I of the Massachusetts 5th infantry. After three months, the men were mustered out of Company I and if they reenlisted, were placed as needed into other regiments. Many of the men became part of Company B in the Massachusetts 5th infantry.