- Seen in: “Ultimate Weapon”
- Previous: Third Battle of Earth
- Concurrent: Blockade of Io
- Next: Battle of Ceres
- War: Neosapien War
- Year: 2120
- Location: Sinope
- Tactical victory: Exofleet, Pirate Clans
- Strategic victory: Exofleet, Pirate Clans
- Pirate Clans
- Neosapien Commonwealth
- Commanding officer
After deciding to ally with Exofleet, Simbacca had the pirate fleet set course for Io. He told J.T. Marsh and Alec DeLeon that he wanted them to train his pilots how to operate the E-frames that had been captured from Typhonus. Meanwhile, the Earth Fleet was returning to Io after being severely damaged during the rescue of Simbacca. Phaeton told Typhonus that he had built a Fusion Pulse Cannon on Sinope and the cannon would destroy the Io base and the pirate fleet.
Deleon told Marsh and Simbacca of his suscipions that a pirate was working for the Neosapien Commonwealth. Typhonus's arrival at Tethys soon after they had arrived meant that he had been informed of the Exofleet mission concerning the alliance. DeLeon suggested having the other pirate ships shut down their navigation and long range communications systems. The fleet would fly in blind formation on Simbacca's trajectory transmitted by beacon.
The Sinope base commander, lacking the pirates location, sent out 2 Neosapien Scout Ships. The scouts flew close enough to the fleet that using the Cloaking Device would not hide the pirate's energy trail. Marsh, DeLeon, and the pirates where sent to destroy the scouts before they tracked the energy signatures. The scouts were able to transmit their location before being destroyed. The majority of the pirates were killed when the second scout ship exploded during a failed boarding operation.
When in range, the cannon was fired and the shot exploded near Simbacca's flagship. The second shot destroyed a destroyer. The remaining E-frames were sent to destroy the cannon since the other ships lacked the speed and manueverability to avoid the fusion cannon's attacks. Further shots destroyed several more pirate E-frames. Several Neosapien E-Frames were deployed from Sinope for close range combat.
Hallas managed to breach the base and entered the energy silo. As soon as he had entered the silo's core, his E-frame was disabled. He then activated his Fusion Pack to self-destruct. Marsh removed the fusion pack and threw it onto the reactor. The detonation of the fusion pack destroyed the reactor's containment systems, and the resulting overload destroyed all of Sinope.
Typhonus, seeing the explosion, ordered the Earth Fleet to attack the pirates, but the debris from Sinope forced him to withdraw. This allowed the Pirate Fleet to escape and rendevous at Io.