By placing it in limelight, Union turned
night into day in Fort Wagner siege

It was a strange invention, but it was the key to the Union’s effort to retake Charleston Harbor.

The dates were Sept. 5-6, 1863. And what made the difference was a calcium light, better known as “limelights.” These chemical lamps used superheated balls of lime, or calcium oxide, to create an incandescent glow. By shining the lights on Fort Wagner, Union forces were able to illuminate their artillery target while simultaneously blinding Confederate gunners and riflemen.

The lights had been used in lighthouses and theaters since the 1830s, but the engineers of Gen. Quincy Adams Gilmore were the first to adapt them for combat. Also called “Drummond lights,” the 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.”

In brief, here’s how the floodlights functioned. Compressed hydrogen and oxygen fed a flame directed at a lime stick. When heated to a point just before melting (4,662 °F), the lime glowed brightly.

Prior to the Civil War, Robert Grant, of New York City, promoted the use of calcium lights to illuminate streets and other outdoor areas. Using a parabolic mirror, he demonstrated the ability to signal ships more than 10 miles out to sea. At the onset of the Civil War, Grant offered his calcium light as a means to enable night combat. Toward that end, in 1862, Company E, 102nd New York Infantry trained to operate with the light. But like many other fringe ideas, this one fell by the wayside.

The idea of turning night into day came up again as the Federals contemplated operations on Morris Island in July 1863. Early on, Brig. Gen. Quincy Gillmore and Rear Admiral John Dahlgren hoped the lights would illuminate targets at night or give the engineers greater visibility while constructing the works. The lights proved less than perfect for these tasks. But with the siege lines closing on the Fort Wagner battery in late August, the Federals turned on the calcium lights again. And this time, the intent was to place the Confederates directly in the limelight.

In addition to focusing on Battery Wagner, the calcium lights also illuminated the ironclads anchored off shore, to aid detection of spar torpedo craft.

In Battery Wagner, the effects of this light hindered operations. Any movement on the parapets, or even opening embrasures to fire, was visible from Federal lines. Not only did this hinder defensive fires, 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 directed fires from Battery Haskell on the calcium light. Neither Federal nor Confederate accounts indicate Manigault’s gunners met with any success.

While there were plenty of examples where combatants had employed light to distract or disorient an enemy going back to ancient times, the use of calcium lights in 1863 was novel to some degree. These were artificial lights, not reflected natural light, and to a higher magnitude.