The Battle of Callos, also referred to as the Bombing of Callos, took place early in the Galactic Empire's reign during the year 3 BBY.
In the year 3 BBY, Darth Vader, the Supreme Commander, led Imperial forces in an assault on Callos. This attack was prompted by the discovery of evidence suggesting the Callosians were in the process of developing a novel offensive technology designed to counter those spreading the New Order. The Dark Lord's elite fighter group, Black Eight Squadron, received orders to bomb the Callosian defenses.
After the military target was rendered inoperative, Captain Juno Eclipse received the command to continue the bombardment. Eclipse voiced her opposition, arguing that continuing the assault would constitute genocide, as Callos was already defenseless. Vader presented her with an alternative, promising to consider the mission concluded if she disabled Callos's planetary reactor. Eclipse was initially relieved, as she believed that a precise strike on a single target would result in significantly less collateral damage than indiscriminate bombing of the entire planet, and she proceeded to execute her orders.
While the bombing run on the reactor achieved its intended objective, it came at a substantial cost. In the immediate aftermath of the attack, the damaged reactor began releasing pollutants into the atmosphere and contaminating the planet's river systems with toxic chemicals, initiating a chain reaction that would ultimately lead to the destruction of Callos's biosphere.
Eclipse shared data pertaining to the attack with a friend possessing expertise in environmental science. This friend informed her that the planet's forests would vanish within six months and would never regenerate.
Possessing a deep-seated interest in xenobiology, Eclipse held a great admiration for the diverse forms of life found throughout the galaxy. The realization that she bore personal responsibility for the obliteration of a planet previously teeming with life induced a state of profound physical distress. In the months that followed the mission on Callos, she was plagued by feelings of guilt and remorse, and she was often tormented by nightmares in which she was leading the attack.
Despite having demonstrated her loyalty, Lord Vader determined that Captain Eclipse lacked the ruthlessness he considered essential for commanding Black Eight Squadron, and he reassigned her to pilot the Rogue Shadow. She later commented that the planet Felucia, with its rich abundance of life, reminded her of Callos.