The Republic Civil War (21 BBY)

The Republic Civil War of 21 BBY was a battle between vessels in the Open Circle Fleet under command of Line Captain Wrendol Toshe and vessels under command of Republic Admiral Talbet in the Mid Rim. 
During a mission to the magma planet Deltiv in the Mid Rim, Republic Forces converged on a magma processing facility under orders from Admiral Talbet to kill all personnel in the station. The civilian workers had been deemed traitors, and the Supreme Chancellor himself asked Admiral Talbet to "make an example" of them. Although the order was given to make an example of the civilians, many toopers in the squad sent to the surface considered this a treasonous act and refused to slaughter the unarmed personnel. These clones rebelled against their leadership, attempting to arrest them for carrying out the corrupt orders. 
The revolt was unexpected and unorganized, and quickly resulted in the clones who acted out being arrested and transferred back to the Phalanx as insubordinate prisoners. They were held in processing until the mission was complete, at which point several of the officers who had been working on the surface of the planet also revolted upon returning to the ship, and released the prisoners from their cells.
After the prisoners were released from their cells, a team was formed mixed of several members of Aurek, Besh and Zerek companies, as well as one navy officer, Commodore Josef Styke. Commodore Styke was the officer working as overseer of Trebuchet on behalf of Admiral Talbet, but began working with the rebels once he realized that the orders he was carrying out were falsified. 
Once the prisoners were released, a firefight ensued in the cell block resulting in casualties on both sides, although the rebels managed to push their way to the turbolifts in the hallway allowing Commodore Styke to get onto the bridge. Once on the bridge, the Commodore sent an encoded transmission to Captain Adein Weiss containing information on the situation and a request for help. The Captain deemed this a priority, and diverted three Acclamator-Class Assault Ships to the Phalanx to assist in arresting the Admiral. 
By the time the reinforcements arrived, firefights were taking place throughout the entire ship as rebels and loyalists clashed. Within minutes, most of the loyalists were pushed back and the bridge was taken over by rebels. During the firefight, the Admiral was able to contact his own fleet and make his way to a docked ship in the lower hangar of the Phalanx, attempting an escape. The Phalanx maneuvered alongside the three Acclamators into a combat formation, as three more Acclamators and a Venator loyal to Admiral Talbet arrived out of hyperspace. Captain Weiss attempted negotiations, but was swiftly met with a slew of turbolaser fire. Fighters from both sides were scrambled, and a large space battle ensued. The odds were even, but the Phalanx and Weiss' ships came out on top suffering significantly fewer casualties. 
During the battle, a separatist cruiser emerged from hyperspace in an attempt to attack the Phalanx, but was disoriented by the situation and was destroyed before it could even scramble its fighters. Separatist involvement proved insignificant to the outcome of the battle. 
After the Separatist ship was destroyed, and Admiral Talbet's fleet was crippled, Captain Crackerjack of Besh Company activated a tractor beam that locked onto his attempted escape crash and pulled him back on board, where he and his crew were arrested for high treason. The rest of his surviving men were individually processed and sentenced accordingly on Coruscant. 
The battle was over as quickly as it started, with the rebel forces emerging victorious, and the Admiral being sentenced to life in prison for his crimes. Supreme Chancellor Palpatine himself reviewed the case, and pardoned the Phalanx and everyone who assisted her crew of their accusations.
During later review of the cases, it was proven that the Admiral falsified the initial orders, and Republic Intelligence agents reviewing the case reported that the documents coming from the Chancellor had no line stating they were to kill anyone.