Ground was broken for Fort Knox in 1844. Looming over the Penobscot River at the town of Prospect, Maine, Fort Knox was intended to prevent a seaborne enemy from sailing willy-nilly up the river to the state capital of Bangor, which the British had achieved during both the American Revolutionary War and the War of 1812.

Fort Knox wasn't completed in time to prevent the Confederate Navy from capturing Bangor during the US Civil War, but fortunately the Navy in Gray wasn't capable of such a feat under the best of circumstances, so the fact that Fort Knox was unarmed wasn't an issue.

Ten, 10" Rodman Guns finally showed up at Fort Knox in July of 1863. These were mounted at the fort's two water batteries, outside Fort Knox' walls. Another 64 Rodmans trickled in over the next 10 years, mostly 10" but also a few of the big 15" variant.