The clash known as the Battle of ThonBoka unfolded in 3 BBY. It pitted the indigenous Oswaft against a coalition comprised of the Centrality (a client state serving the Galactic Empire) and the Renatasian Confederation. The battleground was ThonBoka, a distinctive sack-shaped nebula inhabited by the colossal, spacefaring Oswaft. While the Centrans had been aware of the Oswaft for generations, Emperor Palpatine only learned of their existence shortly before Lando Calrissian's arrival on Dela III, the Centrality's financial center.
Emperor Palpatine, driven by his distrust of a sentient alien race possessing hyperspace capabilities and physical forms superior to starfighters, commanded the Oswaft's extermination. To achieve this, the Empire and the Centrality established a blockade at the entrance to ThonBoka, deploying five hundred capital ships. Carrack cruisers underwent modifications to contaminate the "interstellar plankton" that drifted into the nebula, aiming to starve the Oswaft into oblivion. However, one young adult Oswaft named Lehesu, who had ventured outside the nebula and befriended Lando Calrissian, sought to save his people. Utilizing a transceiver provided by Calrissian's droid ally, Vuffi Raa, Lehesu contacted the Millennium Falcon and pleaded for assistance.
Calrissian successfully infiltrated the blockade by feigning to be a trader offering wares to the very ships that formed the barrier. Despite an inspection of the Falcon, the true purpose of the blockade remained unknown to those below the rank of Admiral. Consequently, no one suspected that the ship's actual cargo consisted of ordinary waste from its trash and toilet recyclers. After maneuvering to the front of the blockade, Lando made a daring escape into the mouth of ThonBoka. Once inside, he established contact with Lehesu and the powerful Oswaft Elders. He then taught them the game of Sabacc, and the group began devising a plan.
However, some Oswaft attempted to negotiate with the picket fleet. The Empire, committed to complete annihilation, responded by destroying the negotiators. In the process, the Oswaft emitted a powerful "shout" that obliterated the unshielded cruiser Courteous with their maser voice-streams. Enraged, the fleet raised their shields and entered the Nebula, but were ordered to retreat by the Centrality's leader, Rokur Gepta. He desired to personally eliminate Calrissian, a long-standing adversary.
Acting on Lando Calrissian's suggestion, the Oswaft launched a counterattack. They secreted heavy metals through their pores and then used their natural hyperjump ability, leaving behind decoy Oswaft between the enemy cruisers. The Imperials, mistaking the decoys for real targets, opened fire, resulting in significant friendly fire casualties. Additionally, the Oswaft utilized their powerful masers to "shout" at the Imperial starfighters, destroying them.
Simultaneously, Klyn Shanga of the Renatasian Confederation pursued Lando and Vuffi Raa with his starfighter squadron, wrongly believing Vuffi Raa was responsible for betraying their world to the Empire. The gambler and his droid defended themselves, destroying several fighters.
After the Imperial fleet suffered an 11% reduction in forces, the battle paused with the arrival of Rokur Gepta aboard the Wennis, his flagship. Gepta then demonstrated the devastating power of his life-destroying weapon, the electromagnetic torpedo, by obliterating the remaining Oswaft Elders and many other Oswaft. The Sorcerer of Tund presented Calrissian with an ultimatum: engage Gepta in personal combat, or Gepta would annihilate all life within the nebula.
Calrissian and Vuffi Raa (who was permitted to participate because Gepta believed he could reprogram the droid to betray his master) confronted the Sorcerer of Tund in the vacuum of space. Following extensive maneuvering and various ploys, Gepta was distracted by his former ally, Klyn Shanga. Shanga had come to the realization that his true target was not Calrissian's companion Vuffi Raa, but rather Gepta's advisor, Osuno Whett.
Shanga forced Whett's pinnace to collide with Gepta's unshielded command ship, resulting in the destruction of both vessels. As Gepta was distracted, Calrissian managed to land a stray shot on his ankle. The Sorcerer's form rapidly deteriorated, but he managed to shoot Vuffi Raa before disappearing, leaving behind an apparently empty space suit. Calrissian examined the space suit and discovered an injured snail-like creature where his shot had struck. He realized that Rokur Gepta was not a humanoid, but a small, repulsive alien known as a Croke from the planet Crakull in the Unknown Regions, a place Lando had visited in the past. Calrissian squeezed the alien until the last Sorcerer of Tund was reduced to a mere stain on his gloves.
At that moment, the battle resumed, but only briefly. Suddenly, a multitude of fifty-kilometer self-aware droids materialized, demanding on all channels that the combatants "Cease fire immediately or be destroyed!" They belonged to a race of sentient droids called the Silentium and were led by The One (Vuffi Raa's creator) and The Other. They had arrived to retrieve their offspring.
The Imperial/Centran fleet, confronted by thousands of gigantic ships, abandoned their genocidal mission and retreated. Vuffi Raa's progenitors repaired the damage inflicted upon him by Gepta and departed with him into the Unknown Regions after sharing a game of Sabacc with Calrissian. As a reward for his efforts, Lando left ThonBoka with a cargo hold filled with valuable Oswaft-synthesized gemstones.
The precise classifications of many of the Imperial ships involved in the battle remain uncertain.
The blockading fleet was documented to consist of 500 large capital ships. The cruiser Respectable, which Lando initially boarded, featured a docking bay exceeding 200 meters in length from the stern bulkhead to the closing hangar bay doors. The size of the hangar and the closing doors suggests it may have been a Venator-class Star Destroyer or a similar variant. This is further supported by the naming conventions used for the cruisers observed during the battle, which appear more aligned with the Republic than the Empire.
Given that this event occurs early in the Expanded Universe, the term "cruiser" may be used in the same context as Han Solo used it in Episode IV - referring to an Imperial-class Star Destroyer. At least one Star Destroyer, the Eminence, was present during the engagement.
Lando makes no mention of any differences between the three other cruisers he visited and the Respectable. One source indicates a substantial number of Carrack-class light cruisers were part of the blockade, but it is unclear whether these were included in the total capital ship count. Considering the size of the cruisers in relation to the Oswaft, the tactics employed by the Oswaft during the battle would have had limited effectiveness if most of the cruisers had been Carracks. The Carrack cruisers should have been able to target portions of an Oswaft that were not necessarily obscured by another cruiser.
Dreadnaughts are also referenced in the battle. While an illustration depicts several ships that appear to be Dreadnaught-class heavy cruisers, a particular phrasing in the book is noteworthy. The fifty-kilometer Rest are described as dwarfing the deceased Oswaft Elders and even the largest dreadnaughts in the fleet. This implies that the largest dreadnaughts were larger than the kilometer-plus Elders and presumably also ISDs like the Eminence.
The Wennis presents another intriguing case. Dating back to approximately 78 BBY, it seems to have been an unidentified type of large Republic battle cruiser that bore a resemblance to a Star Destroyer.