oil rig base complete with vertibird, you get it by doing a quest where you have to kill every npc at enclave, kill the head guy downstairs and get the vertibird key from his body. Using this on the vertibird will transport you to the offshore platform with your party with no means of return or reinforcement. From here you will have to kill the enclave inside and eventually reach the computer and use science on the terminal to reprogram the defenses and make it yours. At this point the terminal will prompt you to input your faction name, this will override the party member's current alliance. The vertibird will just be a static object that can be used to instantly transfer from the base to a landing strip on shore where a similar vertibird is sitting on a landing spot. It will just serve as a main entrance essentially. It should be hard enough that it will take 10 people to do.