Manuscript sketch, January 1864, titled "Signal Tower, Otter Island, S.C.," and approved by Colonel Ed[ward] W[ellman] Serrell (1826 - 1906), First Regiment, New York Engineers.

According to a report submitted by Serrell to his superiors on 6 January 1864, this structure was one of a series of signal towers built by Union army engineers that stretched from Folly Island (Charleston County, S.C.) to Hilton Head (Beaufort County, S.C.). Serrell's report also noted that the tower on Otter Island, located in St. Helena Sound between Edisto and Hunting Islands, was 142 feet tall and was "stockaded, and could, with a good garrison, hold out against an attack of the enemy for some considerable time."

Portions of the First Regiment, New York Engineers, participated in the capture of Port Royal Sound (3 - 7 November 1861) and were stationed on the South Carolina coast for the remainder of the war.