Operation Guardian

Operation Guardian, also known as Project Guardian, was a Starfleet military engagement that was orchestrated in the alternate War of the Prophets timeline which was tasked with combating the Bajoran Ascendancy and their plans of a merger between the Blue Wormhole and Red Wormhole which would have destroyed the entire universe.

The operation was under the command of Admiral Kathryn Janeway who led joint Federation and Borg forces that clashed with the Grigari around the planet where the Guardian of Forever was located. The purpose was to secure the ancient device and use its time travelling capabilities to alter the timeline.

The Operation saw 50 to 60 starships, which included several Borg Cubeships to regain the Guardian of Forever. The battle lasted for several days with the allied forces managing to land ground troops on the planet. However, just as they were within sight of the Guardian, the Grigari activateed a Singularity bomb that destroyed the allied forces, the Guardian and even the Grigari themselves which ended another one of Starfleets desperate plans to survive.

(DS9 novel: Millennium The War of the Prophets)


 * Its entirely possible that these were not a reformed peaceful Borg Collective but rather a splinter group of Rogue Borg such as the Independent Nation of Borg. Though it is possible that the Borg engaged in an alliance with Starfleet in order to prevent the universes destruction.