Robert Grant’s Calcium Lights

The American Civil War provided opportunities for many Northern inventors to profit. Before the war began inventor Robert Grant of New York City had advocated the use of his calcium lights to illuminate streets. After the war broke out he encouraged their use by Union forces as a way to facilitate night combat by illuminating the enemy’s fortified heights.

In 1863 the Union employed two of Grant’s Calcium Lights at the siege of Fort Wagner on Morris Island, Charleston Harbor, South Carolina, to partially blind Confederate troops so they could not effectively return fire. The lights were also used against Confederates holding Fort Sumter. Federal troops began using the lights on the night of September 3. The devices helped prevent the Confederates from repairing their fortifications during nocturnal hours because they could be easily seen and targeted by Union soldiers.

Lieutenant Colonel Henry Martyn Hoyt, who would serve as Pennsylvania’s Republican governor from 1879 to 1883, wrote about this system of lighting in describing the actions of his 52nd Pennsylvania Volunteer Infantry during the 50-day siege of Fort Wagner.

“Operations were suspended during the day, for now, everybody was under the musketry of fire of Wagner, at will,” he wrote. “At dusk . . . the process involved great vigilance and more dodging than always comported with dignity. Here . . . was a squad of busy men with shovels – here a party filling sand bags . . . repairing yesterday’s damage . . . there was . . . Professor Grant pouring his powerful calcium light on the ragged eminences of Fort Wagner. Early on the morning of September 5th the work is done, and everything is ready for a final test of the effect of shell on a sand fort. A hundred guns open with their great throats on Wagner, from sea and land. For forty hours its sand boils as a great cauldron; its sand-bags, guns, carriages, and splinters are thrown high in air. All this while no man can live in its parapet, and its garrison lies smoldering in its bombproofs.” The use of Grant’s Calcium Lights proved to be highly effective, prompting Confederate General P.G.T. Beauregard to issue an order to his troops to find the location of the lights and concentrate long-range cannon fire on them until they could be extinguished.

The Confederate forces retreated from Fort Wagner during the night of September 6-7, ending the siege and eliminating one of the Union’s major obstacles to taking Charleston. The deployment of calcium lights greatly aided the Union in forcing the Confederates to withdraw from Fort Wagner.

Richard C. Saylor is an archivist for the Pennsylvania State Archives and author of the national award-winning book Soldiers to Governors: Pennsylvania’s Civil War Veterans Who Became State Leaders, published by the Pennsylvania historical and Museum Commission in 2010.