Invasion of the Kaiphos Occlusion

Early in the Last Great Time War, the Daleks invaded the Kaiphos Occlusion, a pocket dimension where the Time Lords had secreted the resurrection engine of Project Revenant.

The invasion occured at the same time as the resignation of President Livia and subsequent electoral contest between Admiral Valerian and Romana, which was arranged by Livia and the War Council to enable the resurrection of Rassilon. (AUDIO: Desperate Measures)

Prelude
In the lead-up to the Time War's official outbreak, the War Council instigated Project Revenant to resurrect deceased Time Lords. (AUDIO: Celestial Intervention) The Project's resurrection engine was housed in the Kaiphos Occlusion, accessible by a dimension bridge, (AUDIO: Desperate Measures) which the Celestial Intervention Agency discovered was connected to the Death Zone. (AUDIO: Celestial Intervention)

The Dalek Time Strategist discovered the facility's location and devised a plan to claim it for the Daleks, which the Dalek Emperor approved. (AUDIO: Desperate Measures)

Conflict
Overseen by the Dalek Time Strategist, the Daleks gained access to the Occlusion via a time corridor. The Dalek Supreme was dispatched to lead the assault, with the Daleks fielding the largest fleet the Time Lords had seen since the destruction of the Unvoss and Sunari at the official start of hostilities. Led by General Trave, the War Council committed increasing forces to the Project's defence and hoped new engagements in the Medusa Cascade would distract them, however the Daleks kept pushing through the Occlusion.

Believing the Daleks' advance was inevitable, Co-ordinator Romana dispatched her deputy Narvin and agent Karla to destroy the facility and collapse the dimension before the Daleks could claim victory. They found the base empty as the crew had been killed by a wave of Dalek hunter drones and were still in the process of being resurrected. After carrying out her orders to help Narvin rig the station's destruction with chronon mines and breaking the dimension's connection to Galliftey, Karla abandoned Narvin and took the resurrection engine's sentient core into the Matrix, as she'd been instructed by Livia and the War Council. Narvin was rescued by Irving Braxiatel in his TARDIS moments before the station's destruction. As planned the dimension collapsed, killing all the invading Daleks including the Supreme. (AUDIO: Desperate Measures)

Aftermath
As the War Council had planned, Karla used the core she had taken from the engine to enable the resurrection of Rassilon into the body of Admiral Valerian at the moment of his inauguration as President after winning the election.

With the Supreme lost, the Emperor ordered the Time Strategist to appoint a replacement. (AUDIO: Desperate Measures)