Early in the 1970s the Coast Guard developed the Large Navigational Buoy or LNB as a replacement for lightships. The buoys were operated and monitored electronically. About 40 feet high with a like diameter, these buoys had a 7,500 candlepower xenon gas flashing light which was visible at a distance of 10 miles. It also had a fog horn that could be heard 3 miles away. As they were unmanned they were far more economical than operating a lightship.