The Battle of Proxima III, also referred to as The Liberation of Proxima III occurred during the Earth Alliance Civil War.
Following the battle to secure Babylon 5's independence, the Earth Alliance Civil War entered into something of a lull. Clark was too busy securing his hold over Earth and the colonies back home to bother directly assaulting B5, the rebel forces were too scattered to mount an offensive and simply focused on survival, while the Army of Light was caught up dealing with the larger threat, namely the Second Shadow War. Following the Battle of Coriana VI and the exodus of all the First Ones beyond the galactic Rim, Clark launched a campaign of economic sanctions and propaganda attacks against the rogue station, but otherwise avoided direct military action against it. The Army of Light, meanwhile, was slowly building up their forces and waiting for the right opportunity to liberate the Alliance from Clark's regime, rather than attack out of hand.
After Clark-loyal forces fired upon civilians trying to leave Proxima III, John Sheridan decided it was time to step up their campaign to liberate Earth from President Clark's control. The Narn, Centauri and the League of Non-Aligned Worlds scrapped their mutual defense treaties with Earth, and pledged not to take sides in the conflict, while the rebel forces began rallying at B5 to launch their counterattack. It was decided that Proxima III would be the most logical place to begin, given its relative remoteness from Earth, the ongoing struggle for independence already taking place there, and the need to bring the captains who had killed civilians to justice. Six Omega-class destroyers had been stationed just outside the Proxima III jumpgate, enforcing the planetary blockade, and while Sheridan knew that not all of them would fight for Clark and his policies, they would defend themselves if backed into a corner. Thus, Sheridan ordered all his forces not to engage unless fired upon, hoping to give the destroyer group the option to defect or leave the area without violence.
After sending three White Star class vessels to jump into the Sol System and divert as many Clark-loyal forces away from Proxima, Sheridan set out to the colony with a fleet of White Stars and several squadrons worth of Starfuries and Thunderbolts under his command. His plan was to split the enemy's forces with several waves of White Stars, then surround and isolate each group and force them to surrender. While he hoped to minimize causalities on both sides if possible, Proxima III would be liberated, one way or another.
At the start of the battle, the EAS Pollux, along with the EAS Nemesis, are ordered by Captain Trevor Hall of the EAS Heracles to investigate the first wave of White Stars, which had jumped into the system on the opposite side of the Proxima III from the blockade fleet.
As the second wave of White Stars jumps into the Proxima system, Captain Hall orders the EAS Vesta and the EAS Juno to launch fighters and take point at the second wing. She was then ordered to turn and engage the third, main wave of White Stars, which had jumped in through the local Jumpgate, to the rear of the blockade.
Captain MacDougan breaks radio silence and opens communications with Captain Sheridan. Following this conversation, MacDougan refuses to engage the White Star fleet, feeling that it would be an action in support of illegal orders. Hoping to force the issue, Hall orders the Heracles to engage. He also promotes Commander Robert Philby and ordered him to take command of the Vesta. He proceeds to bring the Vesta into the fight, but only for a short time.
Wishing to determine loyalties, Sheridan orders the White Star 2 to fly past the Furies while infomring Captain Eckland he is simply determining her stand. The Furies does not take action and is declared noncombatant. Meanwhile, the crew of the Vesta subdue Commander Philby and return command to MacDougan. He orders the Vesta to stand down, and declares his ship non-hostile to the White Star fleet. Meanwhile, the Juno, having never engaged, proceeds to the Jumpgate. It is allowed to leave unmolested.
Later, the Heracles knocks one of the White Stars out of control, causing it to crash into the fore of the Pollux. The impact results in her destruction with all hands, as none of the crew had time to get to any lifepods. Originally only advancing with the Pollux, the Nemesis eventually engages Sheridan's forces. She takes severe damage and later surrenders.
At this point, five of the six destroyers are out of the fight: one destroyed, one withdrawn, three stood down. Only the command ship Heracles remains in combat. Captain Sheridan orders her to return control of Proxima III to its lawful government, recall all fighters, and surrender. Captain Hall refuses to comply, knowing that he would stand trial for his actions in the blockade and is thus doomed in any event. His second in command, Commander Sandra Levitt, relieves him of command rather than have the entire crew lose their lives due to his refusal to face the consequences of his own actions. She then complies with the surrender order.
Following the battle, Captain MacDougan of the Vesta and Captain Kawagawa of the Nemesis signed on with Sheridan's forces in their campaign to liberate Earth. The Furies would remain to help the newly arrived EAS Alexander to protect Proxima III from further aggression. Commander Levitt took the Heracles to Beta IX for repairs, then withdrew her from the field until the end of the civil war. The battle was a victory for the Army of Light, but Sheridan lamented the fact that so many lives had been lost in order to achieve it. Proxima III would retain its independence for the rest of the war.