Gen. Edward Porter Alexander was a colonel at Knoxville, in charge of Longstreet’s artillery, where he put to good use the signal flags he’d learned to use as a U.S. Army officer under Albert J. Myer, an army surgeon, before the war.

“I was one of the very few, if not the only Southern officer who knew Myer’s system of signals,” he wrote in his memoir Fighting For The Confederacy.

“Both the Union and the Confederacy,” writes Trevor at Fold3, an online archive of military records, “developed an army Signal Corps during the Civil War. The job of the Signal Corps in both the North and South was to quickly and accurately relay information and orders between the commanders of different units within the two forces (which was especially crucial during battles). The main way they did this was through the use of a flag system called wig-wag…”

At Knoxville Alexander used them for signaling his widely-spread artillery when to cease and recommence firing.

“Then,” recalled the novel’s fictional artillery Sergeant Pitchigru Pease of Parker’s Boy Battery, which was perched on Cherokee Heights above the battlefield, “we saw a flurry of signal flags down at the Bleak House, the red and white flags that Colonel Alexander had first used for instant communication at First Manassas. They seemed to be speaking to us, as well as the rest of the battalion, for then, to the dismay of all, Captain Parker ordered us to cease fire.”

But before long, the guns roared out again in support of the attacking Confederate infantry.

“Then the big red and white wig-wag flags of the battalion atop the Bleak House mansion fluttered into motion,” Pease continued. “The waving flags were sending signals to the batteries in the north, since the fog had lifted some more. I wished I had ever learned to read the flags, but they were awful complicated. Their meaning was hidden from me.”