The Callisto Incident was a violent encounter between forces of the Unified Earth Government and local terrorists from Levosia in the 26 Draconis system, ultimately inflaming violence across the Outer Colonies and triggering the Insurrection. While patrolling the 26 Draconis system, the corvette UNSC Callisto conducted an inspection aboard a merchant ship that turned tragically violent when shots were fired, resulting in thirty deaths.
Callisto would later be hijacked by terrorists, forcing the United Nations Space Command to respond by deploying a battle group of three destroyers. The following engagement resulted in the destruction or crippling of all four warships involved, with Callisto disabled by the destroyer UNSC Las Vegas under the command of Lieutenant Preston Cole.
In January 2494, the distant Outer Colony of Levosia in the 26 Draconis system was suspected of diverting refined selenium and technetium—utilized in the manufacture of Shaw-Fujikawa Translight Engines—to the black market to yield massive profits. Aside from lost taxes, the Unified Earth Government realized that it could not allow slipstream space engine components to fall into the hands of the growing rebellious factions throughout the Outer Colonies; in response, the United Nations Space Command sought to investigate the matter. The UNSC's Central Command ordered the UNSC Navy to blockade and search all ships in the 26 Draconis system for suspected contraband.
The corvette UNSC Callisto was patrolling the 26 Draconis system, when the corvette stopped and performed a routine inspection of a trading vessel by boarding the ship and searching its cargo. The merchant crew of the vessel was nervous due to rumors of impressments during similar searches in the Outer Colonies. Some at ONI would later suspect that this rumour was deliberately started by rebel sympathizers. The inspection went tragically awry when a weapon was drawn and shots were exchanged, resulting in the deaths of three naval officers and twenty-seven merchant crewmen; no contraband was located on the trading vessel. This incident sparked outrage throughout the entire 26 Draconis system and the rest of the region.
Thirty-seven days later, Callisto ordered a similar merchant ship to stand by and allow an inspection and the crew of the trading vessel courteously allowed naval officers to board. However, when the officers entered the cargo bay, they found it empty. Suddenly, the bay doors opened and the officers were ejected into space. The "merchant" crew then boarded the unsuspecting Callisto and murdered the remainder of her crew. Callisto was now hijacked by local terrorists, with her computer system gutted and replaced. As the terrorists began using Callisto against UNSC forces in the system, the UNSC responded aggressively, sending a battle group of three light destroyers tasked with locating Callisto. The battle group was led by Captain Harold Lewis of UNSC Las Vegas, and also consisted of UNSC Buenos Aires and UNSC Jericho.
On March 2, 2494, Las Vegas, Buenos Aires, and Jericho arrived in the 26 Draconis system; the battle group soon located Callisto at 0315 MST. Realizing that the UNSC ships had located them, the rebels aboard Callisto moved the corvette towards a nearby asteroid field. Captain Lewis and Commander Rinkishale of Las Vegas determined that they needed to engage the corvette before she entered the asteroid field, otherwise Callisto would be able to "play cat and mouse" with the UNSC battle group. As Callisto neared the field, the corvette slowed and allowed the battle group to catch up. Lewis had all three destroyers in the battle group prepare to fire six of their seven Ares missiles at Callisto once they were within range. At 0317 MST, the battle group fired eighteen missiles at Callisto as the corvette advanced towards a city-sized asteroid. Suddenly, the corvette rolled and executed a slingshot orbit to the far side of the asteroid. As the missiles recalculated their targeting solutions around the rock, a nuclear weapon preemptively placed inside the asteroid detonated and blew the rock apart, destroying the missiles and launching debris towards the battle group. Buenos Aires, having been the forward-most ship, was obliterated, while Jericho was damaged and Las Vegas was hit by a glancing blow that crumpled her hull. The damage Las Vegas sustained killed Lewis, Rinkishale, and the rest of the bridge crew except for Lieutenants Preston Cole and Jorgenson, though the latter was rendered unconscious. Callisto, unscathed, angled out of the asteroid field and turned to face the remaining UNSC warships.
Callisto engaged Jericho, and the two ships exchanged missile fire, before the corvette succeeded in disabling the destroyer. Meanwhile, aboard Las Vegas, Cole ordered all surviving crew members to the bridge. However, Callisto soon fired a missile upon Las Vegas, disabling the destroyer. At 0348 MST, as per MIL JAG Order TR-19428-P, Cole took command of Las Vegas as the destroyer sat dead in space. Knowing that the insurgents would be unable to resist capturing a destroyer, Cole signaled the unconditional surrender of Las Vegas to Callisto and requested immediate aid for the wounded. As Callisto docked with Las Vegas, the insurgents offered to evacuate the injured to Lawrence Space Station if the crew of Las Vegas offered no resistance; Cole accepted. However, he had earlier ordered the crewmen to remove the ship's last Ares missile from its silo and transport it to the cargo bay Callisto was to dock with. Cole had the missile fired directly into the corvette, crippling Callisto and forcing her surrender.
Following the Callisto Incident, the UNSC began to crack down on dissent throughout the territory, sparking rebellion throughout the Outer Colonies. It would be the Callisto Incident that sparked the Insurrection, a massive civil war that waged across the human colonies. The incident had woken humanity from "complacency", as both the UNSC and the various insurgent factions began fighting and learning various tactics of space warfare, which had been largely hypothetical up until this point. The fact that the Levosia terrorists had realized that nuclear weapons were not as effective in space, and instead planted a device within an asteroid to provide reactive mass to destroy one UNSC warship and cripple two others was noted to be a surprisingly intelligent tactic.
Preston Cole's actions during the Callisto Incident were also considered a tactical leap of insight. Cole had faked a distress signal to lure Callisto closer to Las Vegas to allow him to cripple the corvette, however the action was a severe breach of Common Space Law. UNSC Central Command dithered over whether to award him the Legion of Honor or to have him court-martialed. Ultimately, Central Command did neither to avoid setting a difficult precedent. However, from that point on, Cole could never again send a distress signal in enemy territory; he suspected that no one would believe it. Cole was quickly promoted, though not without protest, and later further promoted to commander and given command of a small corvette to patrol the Outer Colonies.
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