English: The structure depicted by Eastman is the third fort constructed on the same site with the same name. In 1775, recognizing the necessity of protecting harbors from British occupation, the General Assembly of Connecticut ordered fortifications prepared between the mouth of the river Thames and the town of New London. Named for Governor Jonathan Trumbull, the first Fort Trumbull, completed in 1777, was apparently a primitive affair designed solely to cover the river. Its fatal flaw, an open landward side, allowed British forces, led by the American Benedict Arnold, easily to overrun the fort's 23-man garrison from the rear and put New London to the torch in 1781.

In 1812, again responding to the threat of British occupation, a new, more powerful redoubt was erected on the site. Although British warships remained near the mouth of the Thames River for much of the War of 1812, this fort, in conjunction with its companion on the opposite shore, apparently provided sufficient deterrence to prevent the fleet from attempting to enter the harbor. In 1839 a new fortress replaced this second fort. According to the 1870 Surgeon General's report on barracks and hospitals, it incorporated "all the latest improvements in the science of defense and gunnery." The completed 1839 fortress appears in Eastman's painting.