The clash known as the Battle of Serroco, also referred to as the Serroco tragedy and the devastation of Serroco, unfolded during the Mandalorian Wars in 3963 BBY. This conflict pitted the forces of the Galactic Republic against the Mandalorian Neo-Crusaders. The battle took place on the muddy planet of Serroco, situated within the Expansion Region. Admiral Saul Karath of the Republic Navy, anticipating a Mandalorian assault, amassed a battle group to defend Serroco. The Republic Navy strategically positioned its camps adjacent to Serroco's Stereb cities, operating under the assumption that the Mandalorians would avoid jeopardizing the cities to secure the loot contained within. However, this assumption proved incorrect. Upon their arrival, Mandalore the Ultimate, the leader of the Mandalorians, condemned the Republic's strategy as "without honor" and initiated a devastating nuclear bombs bombardment that obliterated the Stereb cities. With Serroco ravaged, Karath reorganized his surviving forces and initiated a retreat, aiming to rendezvous with reinforcements farther from the destroyed planet. The Mandalorians relentlessly pursued, eventually overtaking Karath's flagship, the Courageous, in the depths of space. The Courageous sustained extensive damage and was subsequently boarded, with Admiral Karath narrowly escaping with his life. The Republic vehemently denounced the destruction of Serroco as an act of barbarity and a violation of established norms, and the memory of Serroco became a powerful symbol for the Republic throughout the remainder of the conflict.
In 3976 BBY, the Mandalorian warrior clans, under the leadership of their supreme commander Mandalore the Ultimate, initiated a campaign to conquer independent worlds situated in the Outer Rim. With the Galactic Republic not responding to their initial conquests, the Mandalorians shifted their focus towards the Core, posing a threat to resource-rich planets near the ecumenopolis of Taris. The Republic finally responded by deploying Republic Navy forces to the front lines to confront the Mandalorian Neo-Crusaders. Open war erupted in 3964 BBY, with the Mandalorians launching a three-pronged offensive with the goal of capturing Taris. They swiftly conquered planets like Vanquo, and besieged and occupied Taris. From there, the Mandalorians began to advance inwards. In 3963 BBY, the Mandalorians, advancing from their base of Jebble, turned their attention to the planet Serroco, located in the Ploo sector of the Expansion Region. Serroco, a world characterized by rain, mud, and frequent violent storms, was the original homeworld of the Stereb species. By 3963 BBY, it was a member of the Galactic Republic. Recognizing the impending Mandalorian assault on Serroco, Admiral Saul Karath of the Republic Navy assembled what he termed Battle Group Serroco to defend the planet.
The core of this group was the Inexpugnable-class tactical command ship Courageous, which served as Karath's flagship. The battle group established camps in close proximity to Serroco's Stereb cities, which housed a considerable number of naval personnel along with independent traders who provided food and other services. Notably, Camp Three on Serroco was home to the popular Little Bivoli eatery. Unbeknownst to the Republic Navy, the Little Bivoli was operated by two of the Republic's most wanted fugitives: Zayne Carrick, a former Jedi Padawan accused of murdering his entire class on Taris, and his Snivvian "accomplice" Marn Hierogryph. By positioning their camps near the cities, the Republic hoped to better protect them, believing that the Mandalorians would hesitate to destroy valuable loot. In addition to the Republic Army troopers and Navy shuttles and other craft at the camps, Battle Group Serroco established a blockade around Serroco, utilizing Hammerhead-class cruisers, similarly-designed starships, Foray-class blockade runners, and Aurek-class strikefighters. However, Carrick experienced a vision. While taking a break from his duties at the Little Bivoli, the former Jedi Padawan foresaw that Mandalore the Ultimate would order the destruction of the cities, disgusted by the Republic's tactics. Horrified, Carrick resolved to warn Admiral Karath in an attempt to prevent the impending disaster.
Carrick secured passage to the Courageous aboard the Deadweight, a short-haul craft piloted by Republic pilot Carth Onasi. Upon reaching the bridge, he was immediately recognized as a wanted fugitive. Karath, suspecting Carrick of being a Mandalorian spy, dismissed his warnings. Anticipating the imminent arrival of the Mandalorians, Karath decided to detain Carrick on the bridge of the Courageous to demonstrate the Republic's response to Carrick's "friends." Shortly thereafter, a Mandalorian battle group, consisting of a Kandosii-type dreadnaught and several Jehavey'ir-type assault ships, emerged from hyperspace. The relatively small size of the force piqued Karath's curiosity, as did their positioning at the edge of the Republic force's weapons perimeter. Without warning, the Mandalorian ships launched a barrage of nuclear bombs that appeared to be targeting the Republic fleet. As Karath prepared countermeasures, the missiles abruptly altered course, bypassing the ships. They were never intended for the fleet. As Carrick had foreseen, the missiles struck the planet's surface, causing extensive damage to Serroco's Human settlements and transforming the Stereb cities into desolate craters of glass.
With the Republic force on Serroco decimated by the destruction of their camps by the bombs—their missile defense systems were offline, allowing only eight ships to escape—Admiral Karath was left with no choice but to retreat and establish a new defensive position. As the Courageous group fled, the Mandalorians pursued Karath and his forces through the lanes between Serroco and the banking world of Telerath. Karath hoped to reach the planet Myrkr or the Ryyk Nebula, where he could join forces with the Tremendous group stationed there, but encountered significant challenges. Karath had vowed to prevent the Mandalorians from capturing any of the ships in his flotilla without a fight, and the Courageous engaged in numerous battles to uphold this promise. The Mandalorians eventually caught up to the Courageous in deep space, inflicting severe damage and boarding the crippled vessel. Karath, Onasi, and Commander Dallan Morvis, still alive, decided to scuttle the ship. Facing an onslaught of Neo-Crusader shock troopers, the three retreated from the bridge under intense fire, with Onasi narrowly saving Admiral Karath from a direct attack.
With Mandalorian troopers occupying three levels of the ship, Karath, Onasi, and Morvis gathered a group of soldiers and made their way to the ship's brig, seeking a defensible location. After barricading the door, they proceeded to the prison cells, where Zayne Carrick remained captive and had been meditating. As the Mandalorians approached, Carrick revealed that he had used the Force to gradually loosen bolts in the wall behind his cell, creating a passage to the ship's empty cargo bay. Onasi was able to evacuate Karath, Morvis, Carrick, and several troopers aboard the Deadweight, evading Mandalorian pursuit when the ship was detected leaving the bay. With the loss of the Courageous, the entire Serroco battle group was lost.
After narrowly escaping death aboard the Courageous, Admiral Saul Karath and the passengers of the Deadweight became entangled in a scheme orchestrated by Arkoh Adasca, the head of the medical corporation Adascorp. Adasca aimed to establish himself as a major galactic power by offering the services of the massive and deadly creatures known as the exogorths to either the Republic or the Mandalorians. They confronted Mandalore the Ultimate himself during this process, and in the ensuing chaos, Adasca was killed, Carrick escaped custody, and Karath, Morvis, and Onasi managed to escape. Admiral Karath returned to the Republic capital of Coruscant, and immediately tendered his resignation to the Admiral of the Fleet, who refused to accept it and instead publicly commended Karath for his performance. Having secured victory at Serroco, the Mandalorians advanced Coreward to Nouane, another world that would ultimately be devastated by the warrior clans. Despite the extensive damage inflicted on Serroco by the Mandalorian attack, Carth Onasi successfully saved numerous Stereb lives by relaying warnings from the planet's orbital watchstation and directing them to safety in Serroco's catacombs. Life on Serroco eventually resumed, but the planet's surface suffered irreparable damage. Furthermore, only eight of the ships grounded on the planet managed to escape. One of these ships carried Jedi Knight Meetra Surik, one of several Jedi regularly assigned to the world.
The loss of the Courageous triggered panic on some Republic planets, such as Telerath, and the Republic immediately condemned the "crime" of Serroco's destruction. The Mandalorians melted down the Courageous for scrap, and fashioned part of it into a battle-axe wielded by Mandalore the Ultimate. The memory of Serroco would become a unifying cause for the Republic throughout the war. In transmissions directed at the Mandalorians, Republic propagandist Benegryph Goodvalor named his fictional warship the Serroco, a name that would later be given to a real Republic ship by the time of the Galactic War centuries later. "Goodvalor" was a Serroco survivor—he was Marn Hierogryph, the host of Little Bivoli, who, along with the Trandoshan cook Slyssk, narrowly escaped the carnage by stealing a Republic troop transport, saving half a sleeping battalion in the process. He was celebrated as the "Hero of Serroco" for this act, and the Republic Defense Ministry transformed the event into a propaganda narrative. Approximately a decade after the Battle of Serroco, during the Dark Wars, a group of Republic veterans of the battle formed a gang in the Refugee Sector of the Smuggler's Moon, Nar Shaddaa.
The Battle of Serroco was initially referenced in Star Wars: Knights of the Old Republic II: The Sith Lords, a video game released in 2004. The event was mentioned as part of the backstory of the game's protagonist, Meetra Surik. It was not actually depicted until Knights of the Old Republic 15, a comic written by John Jackson Miller and published in 2007. The actual destruction of the planet occurs in Days of Fear, while the conclusion of the space battle is depicted in a later issue, Knights of the Old Republic 17.