The main line extended 12 miles from Yorktown to the Warwick River and downstream to Lee's Mill, then westward to Skiffe's Creek, which flowed into the James River at Mulberry Island, where the line was anchored on the east by a four-gun battery at Mulberry Island Point. The south end of Mulberry Island (now part of Fort Eustis) is located at the confluence of the Warwick and James Rivers.