When White Forest successfully launched the rocket and closed the superportal, everyone in the Resistance thought they were one step closer to a possible eventual final victory against the Combine. Unfortunately so too did the Combine, and they responded as such, City 17 and the surrounding area was locked down, bringing in reinforcements from around the globe to keep the city contained and squash any Resistance elements within. Of course this meant the plan to find the Borealis, and keep it out of Combine hands would fail unless something was done quickly.

The decision was made to put everything they had into getting a team out of the city to hopefully get to the Borealis, and secure it before the Combine can use whatever Aperture had on the ship. The plan was drawn up quickly, they'd send a massive force led by Gordon Freeman so the Combine would believe it's importance to attack Combine locations on the southern end of City 17 this would draw forces from across the area to them to reinforce. Meanwhile a small but well equipped team would slip out of the city to the north. Once they got out it'd be up to them to reach the Borealis using the coordinates provided by Dr. Mossman by whatever means they could, eliminate any Combine element, and secure the ship's cargo.