Robert Frank Twombly was born around 1843 in New Hampshire to Benjamin and Rosamond Twombly. His father was a farmer who owned $1,000 of real estate and $300 of personal property by 1860. The family lived in Barrington, New Hampshire, until the 1850s, when they moved to Tamworth, New Hampshire.
He enlisted in the Union army on November 22, 1861, and he mustered in as a private in Company G of the 2nd United States Sharpshooters on December 12, 1861. In November 1861, he informed his sister that he had enlisted without their father’s knowledge or consent. He explained that “I had made up my mind to go if I had to run away.”
He remained devoted to the Union. In July 1862, he declared that, "if I could have my discharge ofered me to day I would not take it...I enlisted to fight, and I have not yet, but I want to, and mean to before I come home." The following month, he added, "if my life was required to save the Union I would freely give it. it may not be called for, but however I enlisted to fight and to see the thing through safely." The regiment took part in the Peninsula campaign, the Second Battle of Manassas, and the Battle of Antietam. He died at Antietam on September 17, 1862. According to his tombstone, he was “killed while pulling down the rebel flag at the Battle of Antietam.”