This quest is started by speaking with Major Polati at Camp Forlorn Hope. He has a few tasks that he wants to get done.
Speak with Quartermaster Meyes about the supplies. He will state that there was a group sent to Helios One to collect them, but hasn't returned. He will send you to Lt. Haggerty at Helios One. When you speak with her, she will mention there is a GPS tracker in the supply crate. When you reach it, you can retrieve the supplies, but will be ambushed by the Legion. Return the supplies to complete this portion of the quest.
Major Polati will also ask you to help Dr. Richards in the medical tent. You need a medical skill of at least 20 to help (or otherwise lie) to attempt treatment, although there is no penalty for being unable to help. Aside from Med-X and a Super Stimpack, all equipment within the tent will be available to use for treating the patients. Treatments are performed by sufficient medical skill, or by using the medical equipment.
Polati's next task is to attack the Nelson. He asks you to meet up with Sargent Cooper to the south, where you can ask them to either attack from the north or the east. The north path is the more direct approach, while the eastern path allows you to snipe at the enemies before attacking them. Once you enter Nelson, you need to defeat Dead Sea, and report back or Polati when done.