 The fort was nearly doubled in size by 1864 under Army engineer Major Charles E. Blunt, with a bombproof shelter added.A report on the fort's armament dated January 31, 1865 shows one 24-pounder smoothbore gun, eight 24-pounder rifled guns, and three 32-pounder rifled guns.From May 16, 1864 to August 15, 1864 Fort Sewall was garrisoned by the 11th Unattached Company of the Massachusetts Volunteer Militia (formerly Company I, 8th Regiment Massachusetts Volunteer Militia).