The lock at Delaware City was once the eastern gateway to the Chesapeake and Delaware Canal, one of four locks that regulated water depth so vessels could make the 14-mile journey between the Delaware River and the Chesapeake Bay. Men digging by hand cleared the original course of the canal in 1829, but they could not dig deep enough to create a sea level route across the Delmarva Peninsula, so four locks were built to raise ships from sea level to the higher inland canal and lower them again. The locks at Delaware City and St. Georges had a lift of 6 to 8 feet, while the two locks at Chesapeake City had a lift of 14 to 16 feet. Originally each lock measured 100 feet long, 22 feet wide, and 10 feet deep, but in 1854 the company enlarged them to 220 by 24 feet, with a depth of 10 feet, because vessels using the canal were increasing in size. In 1927, the U.S. Army Corps of Engineers used steam-powered dredges to widen and deepen the canal into a sea level waterway over its entire length, making the locks unnecessary, and relocated the canal's eastern entrance to Reedy Point, two miles south of Delaware City. This single surviving lock was preserved in place as a remnant of the canal's earlier days. In 1975, the Department of the Interior placed the Delaware City lock on the National Register of Historic Places, and in 1985 the American Society of Civil Engineers named it an Historic Civil Engineering Landmark. Ships entered the lock through gates at one end at sea level, the gates closed, water was pumped in to float the vessel upward to the canal's higher level, and when the water reached that level the gates at the far end opened so the vessel could exit onto the canal. The canal company also created a 90-foot-wide turning basin just inside the lock where ships and barges could be turned or moored while awaiting passage and where vessels from the Delaware River could find safe harbor in severe weather. Workers using a diving bell descended into the canal inside a large bubble of air to clear debris blocking the lock mechanism or make repairs, though diving bells were seldom used after the diving suit was perfected in the early 20th century. The current entrance on the Delaware River, dating from 1927, connects the river with a narrow branch of the original canal and allows small craft to navigate inland for two miles to connect with the wider and deeper modern canal.