The Battle of Kashyyyk was a major engagement during the New Sith Wars between the Brotherhood of Darkness and the Galactic Republic. In 1003 BBY, the Brotherhood of Darkness set its sights on the Republic stronghold on the Wookiee homeworld of Kashyyyk, hoping to gain a foothold in the Mid Rim. At first, the Republic used Kashyyyk's great wroshyr forests as a staging point for ambushes and guerrilla raids on the Sith with great success, causing thousands of Sith casualties. During the battle, a Sith unit called the Gloom Walkers was separated from the main Sith force, but one of their number, Dessel, was able to lead them back to the Sith army. The story of the Gloom Walkers helped to greatly raise Sith morale and inspired the Sith to win the battle and capture Kashyyyk.
For a thousand years, the Sith and the Galactic Republic did battle in the conflict known as the New Sith Wars. In 1010 BBY, a former Jedi Master, Lord Kaan, reorganized the Sith into the Brotherhood of Darkness, an army of Sith over twenty thousand strong. The Brotherhood of Darkness began a new campaign against the Republic, scoring many victories. In 1003 BBY, the Brotherhood of Darkness set their sights on the heavily-forested Wookiee homeworld of Kashyyyk, hoping to secure a foothold in the Mid Rim.
That year, the Sith invaded the system, sending in wave after wave of troops to capture Kashyyyk. However, the planet was a Republic stronghold, one that the Republic wasn't willing to give up even with a disadvantage in numbers. When the Sith fleet first landed, the Republic forces vanished into the great wroshyr forests, turning the invasion into a war of attrition—a long, drawn-out campaign fought in the branches of the wroshyr trees. The Sith troopers were not used to fighting in the treetops, and the thick foliage and kshyy vines provided perfect cover for the Republic soldiers and their Wookiee guides to launch ambushes and guerrilla raids on the scattered Sith forces. The losses to the Sith were catastrophic, with thousands of soldiers being killed, and many died without even seeing the enemy who had fired the fatal shot. Undeterred, the Sith Masters continued to send more troops into the maelstrom.
One of the units in the second wave of reinforcements was the Gloom Walkers, commanded by Lieutenant Ulabore. During the battle, the Gloom Walkers were separated from the main lines of battle, finding themselves deep behind enemy lines. Alone and surrounded by enemies, Lieutenant Ulabore panicked, having no idea what to do to keep his men alive without direct orders. Fortunately, one of their number, a former cortosis miner named Dessel, stepped in and took command. Dessel was Force-sensitive and was able to sense the enemy's whereabouts even when he couldn't see them, allowing the Gloom Walkers to avoid Republic traps and ambushes on their way back to the front lines. It took three days and nights, but the Gloom Walkers were able to rejoin the main Sith force. The story of the Gloom Walkers became a rallying point for the rest of the Sith army, raising morale that had become dangerously low. It took almost two thousand Sith units, but the Sith were finally able to capture Kashyyyk.
After Kashyyyk fell, the surviving Republic soldiers fled to the neighboring world of Trandosha. Twenty units of Sith troopers, including the Gloom Walkers, were sent in pursuit. What ensued was the Battle of Hsskhor, a bloody engagement fought in the desert plains outside the city of Hsskhor. The Sith ultimately won the battle, and Hsskhor was razed to the ground. After the Battle of Kashyyyk, Lieutenant Ulabore was given a special commendation as the leader of the Gloom Walkers; he never bothered to mention that Dessel had been the one responsible for leading the Gloom Walkers back to the main Sith force. However, he later promoted Dessel to sergeant.