How An Intelligence Coup Won The Confederacy Charleston Harbor

May 13, 2020 Topic: History Region: Americas Blog Brand: The Reboot Tags: Civil WarConfederacyIntelligenceWar

How An Intelligence Coup Won The Confederacy Charleston Harbor

Tasked with preventing the Union capture of Charleston, Confederate intelligence agents mounted a complex effort to crack the enemy signal codes.

Here's What You Need To Remember: The Union forces attempting to seize Charleston were thwarted in large part due to an expertly managed Confederate intelligence operation. From Mickler’s commando operations that captured Jones, identified the signal station, and then snatched Rushby, to Bryan’s human intelligence operation that elicited the signals system’s secrets, to Markoe’s signals intelligence operation that broke the code and intercepted the signals, the Confederates did nearly everything right.

The Union bid to capture Charleston, South Carolina, in April 1863 was set in motion seven months earlier, in the autumn of 1862. At that point, the war was not going well for the Union, and President Abraham Lincoln was looking for a clear-cut military victory to bolster his domestic political support. Assistant Secretary of the Navy Gustavus V. Fox saw an opportunity for the Union Navy to shine by seizing Charleston. The Confederates had fired the first shots of the war there, at Fort Sumter, and Northerners considered the city the cradle of rebellion. Occupying Charleston would be a huge morale boost for the flagging Union war effort.

It was not an outlandish idea. A combined Army-Navy operation had already taken Hilton Head, a short distance south of Charleston, in late 1861 and had essentially closed the port of Savannah with another combined operation a few months earlier. In October 1862, Fox, Secretary of the Navy Gideon Welles, and President Lincoln agreed—Charleston would be the next target. Fox was convinced that the Navy could steal the limelight from the Army at Charleston by using ironclad ships to blast a path into the harbor. He was enamored of the new ironclad warship technology and thought the new craft invulnerable. Multiple hits on ironclads in duels with Confederate gunners at Fort McAllister, near Savannah, in January and March had caused only superficial damage, seeming to prove Fox correct.

The Hole in Confederate Intelligence

With divergent plans in mind, Union ground and naval forces assembled at Hilton Head and spent the winter preparing for the Charleston campaign. The Confederates defending the region knew that they were at an extreme disadvantage.  Looking for any means possible to even the odds against the numerically superior Union forces, the Confederates attempted to gain an edge through complex intelligence operations.  With enemy troops and ships poised to attack anywhere along the Atlantic coastline, the Confederates needed early warnings from Hilton Head of major Union expeditions.  Accordingly, they employed the full spectrum of tactical human intelligence, maintaining a loose cordon of observers in the area and infiltrating at least one spy into the Union ranks to gather information on the island.

The missing piece for the Confederates was signaling intelligence. For several months, they had been trying without success to read Union flag signals. They knew that reading the Union messages would provide the best forewarning that they could possibly achieve. But what were those flag signals, and how did they work?

During the Civil War, both sides used the signal flag or wigwag system developed by Army surgeon Albert J. Myer in 1856. The wigwag system used a single flag moved to the left, right, and center of the signaler. Each series of movements represented a series of numbers which in turn represented a letter, word ending. or phrase. One drawback to the wigwag system was that the enemy was likely to be able to see it. As a result, both sides invested in rudimentary ciphers to counter enemy intelligence. The Union deployed a cipher system centered on a device called the signal or cipher disk. Each Union signal station was equipped with a cipher disk to encrypt and decipher messages. The cipher disk was made of two cardboard disks fastened together. Each time the alignment of the disks was changed, it set a new cipher.

The cipher disk was used within the Union Signal Corps, and instructions demanded that ciphers be changed often.  The frequency and method for relaying the changes were left to the senior signal officer in each command. Union signal officers were required to memorize these cipher instructions to ensure that “in case of capture, no information will fall into the hands of the enemy.” For additional security, Union signal officers were advised, “When there is danger of capture, all messages or important papers must be destroyed,” presumably including the cipher disk. Finally, knowledge of the cipher system was restricted to officers. Enlisted Union signalers merely signaled the numbers read to them by their officers.

In order to intercept and read the Union signals, the Confederates defending Charleston needed to understand the Union cipher system. Analyzing intercepted Union messages had not revealed the secrets of the system. So when the Confederates learned of an opportunity to capture a Union signal officer, they decided to take a different approach to the problem.

The Capture of Caleb Jones

Since late 1861, Hilton Head Island had been a Union forward operating base defended by thousands of troops and providing logistical support to the Union Navy blockading fleet. To maintain communications with defenses on the more remote west coast of the island, the Union Army had established a signal station in the Spanish Wells plantation house overlooking Calibogue Sound. Relatively isolated, the signal station was normally manned by two Signal Corps officers and four enlisted signalmen and defended by several infantry companies.

On the night of February 11, 1863, a two-man Confederate reconnaissance patrol crept ashore at Spanish Wells. The patrol remained hidden all the next day, noting the activity, and took Private Caleb Jones of the 9th Maine Volunteers prisoner, leaving that night. Jones, 45, hailed from Brighton, Maine, and had been in the Army for five months. One of his fellow soldiers wrote that Jones “always talks secesh,” suggesting he sympathized with the Confederates. For the next week, Jones was thought to have deserted. Even after his fate became known, Union officers never seriously investigated the circumstances of his capture.

Perhaps spurred by his “secesh” sympathies, Jones appears to have readily provided what proved to be vital intelligence. Before the reconnaissance, the Confederates had apparently seen a platform built on the roof of the Spanish Wells plantation house but thought it was used only for observing the Sound. The prisoner divulged that it was actually a signal station and that the guard force was not allowed inside, suggesting that anyone inside the house was probably a member of the Union Signal Corps. Finally, the ease with which the patrol entered and left the area revealed that the Spanish Wells signal station was poorly guarded. The poorly protected, isolated signal station at Spanish Wells was a tempting target for Confederates desperately seeking information about the Union signaling system.

Raid on Spanish Wells: “The Surprise Was Complete”

Men from E Company of the 11th South Carolina Volunteers, commanded by 33-year-old Captain John H. Mickler, had executed the February reconnaissance to Spanish Wells. They were local men who knew the waterways and back roads like the backs of their hands. Already experienced raiders and intelligence gatherers, in modern terms these men would be considered commandos. In great secrecy, a select group of E Company soldiers, led personally by Mickler, prepared to capture a Union signals officer from the station at Spanish Wells.

Just after midnight on March 13, 1863, the Confederates returned to Spanish Wells in force. The 25-man raiding party silently landed and surrounded the signal station. They quickly entered the building and captured three enlisted signalers. The two signal officers on duty were upstairs. The station commander, 1st Lt. Milton Fenner, and a fourth enlisted signaler escaped out an upstairs window, but 1st Lt. Thomas Rushby rushed downstairs and was captured. As Fenner reported later that day, “The surprise was complete.”

In less than five minutes, the Confederate mission was accomplished without a shot fired. The raiding party set fire to the house and swiftly returned to their boats, scooping up five guards along the way. While it might seem unwise to take so many prisoners, this was likely part of a deception. By taking both signalers and infantry as prisoners, the Confederates’ true target was obscured.

As the raiding party paddled across the Sound with their prisoners, pandemonium broke out in Spanish Wells. Not observing the retreating boats, 9th Maine troops scoured the area around the plantation house looking for the raiders and their prisoners. The light of the house fire alerted a reserve regiment that also entered the area about an hour later. It was to no avail—the raiding party was gone and the prisoners were on their way to the jail in Hardeeville, South Carolina, about 20 miles to the west.

To Trick the Captured Thomas Rushby

At the time of his capture, Manhattan native Thomas Rushby was 27 years old and had nearly two years of military service under his belt. A combat veteran, Rushby was part of the Union expeditionary force that took Hilton Head Island in 1861, captured Fort Pulaski at Savannah in 1862, and fought in the Battle of Secessionville, near Charleston, in June 1862. Promoted to first lieutenant in October 1862 just before his regiment was transferred back to Hilton Head, Rushby volunteered for signal duty and began training that winter. Rushby was one of several officers recruited for signals duty in preparation for the upcoming Charleston campaign. While an experienced combat engineer, Rushby had been a signal officer for only a few months when he was captured.