The following section contains information from StarCraft: Insurrection.
The 7th Fleet was a small force deployed from Tassadar's Protoss Expeditionary Force under the command of Executor Andraxxus. They attacked zerg-infested worlds in the Brontes system before reaching the source of infestation, Brontes IV. In spite of a strong initial assault, the fleet was weakened due to infighting among their ranks, and was destroyed by the Zerg Swarm.
Arrival on Brontes IV
7th Fleet was a detachment of the Koprulu Expeditionary Force of the Protoss Empire, sent to cull the zerg infestation of the terran worlds. In the early stages of the Great War, Executor Tassadar ordered 7th Fleet's Executor Andraxxus to break off from the main host to secure passage for the main host's return by destroying the zerg forces infesting the Brontes system.
Andraxxus consulted Judicator Syndrea, who suggested isolating the core infestation on Brontes IV. Andraxxus concurred, 7th Fleet secured one of the planet's satellite platforms from zerg control. 7th Fleet then secured the Brontes IV Orbital Relay Center from Brontesian forces in order to prevent terran ships from leaving the planet and spreading the zerg infestation.
With the space around Brontes IV secured, Syndrea suggested that the planet be purified, and that both the terran and zerg on the surface be destroyed. Demioch protested, and Andraxxus agreed the extermination of the terrans would be extreme, and that they should be preserved if possible. Andraxxus then gave command of the vanguard on Brontes IV to Syndrea, who he tasked with establishing a stronghold on the planet while he purged the zerg from the surrounding world. He left three advisors, Demioch, Edullon, and Aedus/Xerxes, to council her. She ordered Edullon to secure New Dresdin, Aedus/Xerxes to purge the infestation in Adbakken, and Demioch to assault the hives in Carvalho. Edullon protested the decision to send Demioch to such a heavily defended region, and suspected that she may be trying to kill Demioch.
Seeds of Insurrection
With the first operations on Brontes IV proceeding successfully, Syndrea ordered Edullon back to the Brontes IV Orbital Relay Center. However, Demioch's forces had been defeated in battle, and captured by a renegade terran faction known as the Fist of Redemption. Syndrea ordered Edullon to give up on Demioch, but she defied orders and searched for her father. On the surface, she encountered Charlie Vane of the New Dresdin Outlaws, who aided her in her search. The two forces broke through the Fist of Redemption and saved Demioch, and Edullon revealed revealed Syndrea's schemes to her father. Demioch stated that they needed to inform Andraxxus.
Meanwhile, Syndrea proceeded with the second phase of her plan, and ordered Aedus/Xerxes to clear out zerg and New Dresdin Outlaw forces in the region where she planned to establish her stronghold. This operation was successful, and a central protoss base was established. The archon was then tasked with stripping a region known as the Valley of the Shadow of resources to prevent their exploitation by the zerg. by the zerg. However, this caused the zerg to become erratic, and push into untainted terran communities and press the borders of the protoss stronghold. Edullon confronted Syndrea, stating that she was at fault. Syndrea declared her and her father heretics, and ordered Adeus/Xerxes to deal with them after it defended their main stronghold. In spite of overwhelming zerg numbers, the defense was successful.
In the aftermath, Adeus/Xerxes informed Edullon that the terran psychic Atticus Carpenter had dominated the will of the cerebrate Auza and was born anew, then telling her that it would have to fight her when they met again. Edullon allied again with the New Dresdin Outlaws and gathered protoss dissatisfied with Syndrea, and combined force devastated Carpenter's Brood.
Adeus/Xerxes then mobilized to attack Edullon and Demioch, and Demioch expressed regret he could not face his old friend and slay it in honorable combat. Edullon stated she would take up the duty of slaying it. The New Dresdin Outlaws and the 7th Fleet rebels halted the advancement of Syndrea's forces, and Edullon faced down Adeus/Xerxes, defeating it and granting it peace.
The Fleet Shatters
With the situation in the Brontes system escalating, the Overmind sent additional forces under a new cerebrate. Syndrea's shattered forces were overwhelmed by the zerg, and she was captured. The main fortress of 7th Fleet was then besieged by the zerg, though they managed to hold their position planetside. However, the battle against Andraxxus's fleets had begun to turn against the protoss, and the survivors mobilized to regroup at Brontes IV as the zerg secured the space around the planet. The survivor's of Syndrea's loyalists began to rally to meet with Andraxxus's forces, but the new cerebrate discovered and annihilated them.
Andraxxus's 7th Fleet survivors met with the New Dresdin Outlaws, and allied with them in order to defeat the zerg. The newest cerebrate and the cerebrate Nargil pushed their position, and broke their offensive. The continued defeats of 7th Fleet pushed Andraxxus to assault both the Zerg Swarm and Carpenter's Brood, and Nargil's Fenris Brood capitalized on his overextension and engaged the main 7th Fleet body. Following a parasite planted in Black Morgan, the Overmind found the final stronghold of 7th Fleet, where the New Dresdin Outlaws retreated to. Andraxxus noticed the parasite within Black Morgan, and recalled his fleets to defend his stronghold, but the zerg broke through their defenses. In a final stand, 7th Fleet was destroyed, and Andraxxus, Edullon and Demoich were slain.