The Craighill Channel starts at the mouth of the Magothy River and extends to the southern end of Belvidere Shoal a distance of approximately five miles. This channel forms the first leg of the maintained channel to the Patapsco River and Baltimore Harbor. The channel was named after William Price Craighill, a major in the Army Corps of Engineers and a member of the Lighthouse Board (the branch of the US Government responsible for lighthouses), who supervised the surveys for the widening and deepening of the channel. On November 10, 1865, Maj. William P. Craighill became the Baltimore District Engineer. Maj. Craighill had more influence than any other person in shaping the city's harbor. He was the District Engineer for 30 years before becoming a brigadier general and the Army's Chief of Engineers in 1895. Craighill's first order of business was to survey the Brewerton Channel to determine the presence of any shoaling. He was alarmed to find that the lower portion of the channel had become very shallow due to the conflicting currents from the Susquehanna and Patapsco Rivers. To prevent this from happening in the future, Craighill proposed a new cut that would alter the existing channel. The new channel would no longer go straight out into the Bay but would run due south for 3 miles and then turn to the southeast. The plan was approved and the new 200-ft-wide by 22-ft-deep channel was dredged and ready for navigation by late 1869. The channel was dredged 169 feet wide and generally 21 feet deep, but the growing importance of Baltimore as a port persuaded Congress to appropriate $50,000 in 1870 to widen the channel to 500 feet and deepen it to 22 feet. In 1872, both Congress and Baltimore City provided more funds for waterway improvements and by 1874, a 24-ft-deep and 250 to 400-ft-wide Federal channel to Baltimore Harbor was completed. The channel continued to be improved; between 1881 and 1884, the Federal channel to Baltimore Harbor was authorized and deepened and widened to 27 ft deep and 600 ft wide. Unlike the Brewerton Channel, which then intersected the Craighill Channel about a mile northeast of Seven Foot Knoll Lighthouse, Craighill had no lights to aid night navigation. The Lighthouse Board stated in 1871 that:

“this channel has the advantage of saving about five miles in distance to large vessels bound to Baltimore from the lower bay; avoids much, if not all, of the dangers usually experienced from the accumulation of ice in the lower part of the Brewerton Channel during the winter; is much easier navigated, or would be if range beacons were established.”

Because of the location of the Craighill Channel and its connection with the Chesapeake Bay, shore range lighthouses would have required very powerful lights and an extremely high rear range light. Thus the range lighthouses were built in the water. Both range lighthouses were originally designed to be screwpile foundation types but the severe ice conditions during the winter of 1872-1873 convinced the Lighthouse Board to build a small caisson structure for the front range and granite pier foundation for the rear range. Upon completion of this new pair of range lights it was thought that "the two expensive lights built on jetties at North Point" would become "unnecessary" and "might be dispensed with." Congress appropriated $45,000 on June 10, 1872 "for two range lights for Craighill Channel into Patapsco River from Chesapeake Bay, to take the place of the two lighthouses now at North Point."