Bartlett initially enlisted in the
4th Battalion Massachusetts Infantry, also known as the New England Guards, which was garrisoned to defend
Fort Independence in
Boston Harbor. At the time, the three forts in Boston were entirely unmanned and Boston harbor almost defenseless. Fort Independence was the only of the three forts equipped with cannon, however most of them were facing the city and not the water.
20th Massachusetts On August 8, 1861, Bartlett was commissioned
captain in a new regiment then forming—the
20th Massachusetts Infantry—and given command of Company I. During the siege, on April 24, 1862, Capt. Bartlett was shot in the left knee by Confederate pickets. The wound required the amputation of his leg. Bartlett returned to Boston to recuperate and, during the summer of 1862, finished his degree at Harvard. Bartlett was placed in command of the 57th which was formed in
Worcester, Massachusetts. The unit was sent to Virginia before it was fully organized, and Bartlett would not receive his new commission as colonel of the 57th until April 9, 1864, although the commission was made retroactive to August 1863. Bartlett returned to the Army of the Potomac in July 1864.
Brigade command Upon his return, Bartlett was placed in command of a
brigade (1st brigade, 1st division of the IX Corps) consisting almost entirely of Massachusetts regiments. In July 1865, the IX Corps was disbanded, however Bartlett remained in the army another year until his resignation on July 18, 1866. ==Post-war career==