Fort Mott was constructed in the 1870s as part of a three-fort defense system for the cities upstream along the Delaware River. It's located near the mouth of the river in Pennsville, NJ, and worked in tandem with Fort Delaware on Pea Patch Island and Fort Dupont in Delaware City, DE. Only two of the 11 planned gun emplacements had been constructed before further construction on the fort was permanently halted. All three forts became obsolete after WWI.