How to unlock: automatically after completing the Precipice of War quest.
- Fly to the Prydwen
- Plant explosives (3)
- Escape the Prydwen
- Talk to Desdemona
Get to the Prydwen
Once you get rid of the Brotherhood of Steel on the Cambridge Police Station roof, enter the transporter with the crew. Together you will fly to Brotherhood's airship - the Prydwen. On the way Deacon will give you a Brotherhood of Steel's costume which you should put on in order to infiltrate the ship without having to fight.
Plant the explosives and escape the ship
Once you land, keep going to the upper deck by following the mission markers. You must plant three explosives in the selected locations on the ship. It is important to avoid all commanders - when you will walk next to them, they will recognize you and commence the attack. The only option to avoid battle in that case is using high Charisma level, but it is better not to risk.
Go back to the transporter after planting the charges. You will fly away and land on a nearby beach. Leave the vehicle and go to Railroad H.Q.
Quest rewards: Experience points, 1000 bottlecaps, Railway Rifle upgrade