ordered to return to the major force and join Banks. The high point of the Union's Red River campaign had been reached. From this point, with falling water levels and increased Confederate shore fire the gunboats would face a desperate battle to avoid being trapped above the Alexandria rapids. In the Battle of Blair's Landing, Lexington silenced the shore battery but the Confederate cavalry poured a hail of musket fire into the rest of the squadron. The rebels fought with unusual pertinacity for over an hour, delivering the heaviest and most concentrated fire of musketry. What Porter described as "this curious affair,...a fight between infantry and gunboats", was finally decided by the gunboats' fire, which inflicted heavy losses on the Confederates, including the death of their commander, General Thomas Green. This engagement featured the use of a unique instrument, developed by Chief Engineer Thomas Doughty of Osage and later described by Thomas O. Selfridge Jr. as "a method of sighting the turret from the outside, by means of what would now be called a periscope..." The high banks of the Red River posed a great difficulty for the ships' gunners in aiming their cannon from water level. Doughty's ingenious apparatus helped to solve the problem. Thus was the periscope, a familiar sight on modern gun turrets and on submarines, brought into Civil War use on the western waters. Upon reaching Grand Encore the fleet faced a dangerous situation. The Red River, normally high until late June, had fallen so much that the gunboats could not pass over the rapids and it seemed that the better part of the Mississippi Squadron was doomed to destruction as the Union Army made plans for evacuation. However, Lieutenant Colonel Joseph Bailey USA, proposed a plan for building a series of dams across the rocks of the falls and raising the water. A center opening would let the ships ride out on the crest of the water. On 9 May 1864, the dam had nearly reached completion but the pressure of the water became so great that it swept away two stone barges which swung in below the dam on one side. Seeing this accident, Admiral Porter mounted a horse and rode up to where upper vessels were anchored and ordered Lexington to get underway. Lieutenant Bache succeeded in getting Lexington over the upper falls, then steered her directly for the opening in the dam