In the Limelight: A Civil War Military Innovation

By Reece Nortum
Hampton Roads Naval Museum Educator

 Certainly you've heard the expression (or a variation of) "You're in the limelight." Did you know that there was such a thing? In 1825, Michael Faraday, the famous English chemist and physicist, demonstrated that if an oxygen-hydrogen flame were directed against a piece of quicklime, the heated lime produced a brilliant yellowish light.  

Once refined, these chemical lamps used super-heated balls of lime, or calcium oxide, to create an incandescent glow. The lights, known as limelight or calcium lights, began appearing in lighthouses and theaters during in the 1830s.

The idea of using the lights to turn night into day occurred to Union commanders in July 1863, as they contemplated operations on Morris Island, located at the outer reaches of Charleston Harbor. Union forces, most notably the 54th Massachusetts Volunteer Infantry Regiment (the famous African-American unit depicted in the 1989 film Glory), had sustained heavy casualties that month attempting to capture Fort Wagner (also known as Battery Wagner) on Morris Island.  Early on, Brigadier General Quincy Gillmore and Rear Admiral John Dahlgren hoped the lights would illuminate targets at night or give their own engineers greater visibility while constructing the works. The lights proved less than perfect for these ideas. But with the siege lines closing on Fort Wagner in late August, Union forces turned on the calcium lights again. This time, the intent was to place the Confederates directly in the limelight.

A night raid upon Fort Wagner (also known as Battery Wager) supported by calcium lights.

In addition to focusing on Battery Wagner, the calcium lights also illuminated the ironclads anchored offshore and to aid detection of spar torpedo craft. Against Battery Wagner, the desired effect of the brilliant light was to hinder operations. Any movement on the parapets, or even openings in bunkers to fire, was visible from Union lines. Not only did this hinder defensive fire, but also repairs to the battery. In reaction, Confederates attempted to extinguish the lights with long range artillery fire. In the early morning hours of Sept. 6, Major Edward Manigault, commanding artillery at Legare’s Point on James Island further inland, directed fires from Battery Haskell on the calcium light. Neither Union nor Confederate accounts indicate Manigault’s gunners met with any success. Gillmore’s engineers were the first to adapt the calcium light for combat, allowing them to illuminate their artillery target while simultaneously blinding Confederate gunners and riflemen.

During the siege of Charleston, the Union Navy also focused “limelights” on Fort Sumter while they pummeled it into rubble. In a dispatch to Captain Stephen Rowan, commanding USS New Ironsides, Rear Adm. Dahlgren wrote from Morris Island, “I have just received your signal dispatch in reference to the use of my calcium light on the New Ironsides. I placed at your disposal with great pleasure, and have little doubt that it will aid you in keeping the torpedo vessel.”  

Dahlgren made the following request to his superiors in Washington D.C. on April 6, 1864:

SIR: I beg leave to acknowledge the receipt of your communication enclosing a suggestion made to the Department that small steams with a calcium light would increase the security of our vessels against the rebel torpedo boats. A calcium light is always kept in operation on board the Ironsides, unless there be a good moonlight, I intended also to mount one on each monitor; the trial was made on one of them [New Ironsides, at the battles at Charleston Harbor], but not continued, because the commanding officer thought it a disadvantage. After a close observation of the one in use, I think it probable that the small angle at which the rays the water detracts from its efficiency. Small steamers are always kept in motion in advance of the picket monitors. As many as six have been on duty in a single night, besides a number of picket boats, making it exceedingly difficult for any object on the water to escape them unnoticed; which is confirmed by the fact that the efforts of the rebels were directed against the Housatonic, which was out in the open sea, while the monitors were inside the bar, within range of the rebel batteries and infinitely of more consequence. If any of the torpedo boats should elude the pickets, they would be stopped by nettings in the vicinity of the ironclads. There is no remedy for the outside cruisers except to be kept constantly underway, and I should pursue the same course inside with the monitors, but it is impossible at night in channels lined with dangerous shoals and heavy batteries. With an increased number of steam tugs and some torpedo boats like those of the rebels, added to the measures already taken, I should feel no apprehension whatever from this base style of rebel warfare. 

With his requests' approval, this new technology was sent to the Norfolk Naval Shipyard for use in the North and South Atlantic Blockade Squadrons. Additional requests came flowing in, after great success was reported in stopping Confederate blockade runners. The order came via the North Atlantic Blockading Squadron flagship USS Malvern that five locomotive lights were to be brought and attached to the bow and sterns of several ironclads within the Hampton Roads area in 1864. During 1864 and 1865, the Navy ordered 300 calcium lights to be installed as standard issue aboard all ironclads built in the area.

These calcium floodlights were later used as searchlights to spot Confederate warships and blockade runners. In early 1865, a Union light even helped detect a Confederate ironclad fleet as it tried to move along the James River under cover of darkness. A Southern officer later noted that a planned sneak attack was made impossible in part because of the Union’s “powerful calcium light.” 

Equipped with calcium lights, the Union Navy was able to continue, even on the darkest nights, the bombardment of Fort Sumter and Battery Wagner, ushering in a decades-long period in which the “Spotlight” was an important and well-used tool for peacetime, and war, aboard naval vessels.