The Lost Patrol

The Lost Patrol is a quest in Fallout 4.

Quick walkthrough

 * 1) Investigate the battle site.
 * 2) Listen to Knight Astlin's holotape.
 * 3) Investigate the Revere satellite array.
 * 4) Follow the radio distress signal.
 * 5) Listen to Scribe Faris' holotape.
 * 6) Follow the radio distress signal.
 * 7) Investigate the battle site.
 * 8) Listen to the Battlefield holotape
 * 9) Investigate Recon Bunker Theta.
 * 10) Speak to OR kill Paladin Brandis, depending on relation to the Brotherhood (ally/enemy).
 * 11) If Paladin Brandis is spoken to: Report to Danse.
 * 12) If Paladin Brandis is killed, the quest is marked as completed.

Detailed walkthrough
The player character will detect a distress signal once they are near one of the three locations that one of the three Brotherhood of Steel followers perished. One at a ruined house next to Knight Varham, The ruined house is north of Relay Tower 0MC-810, south of Greentop Nursery and east of Taffington boathouse.

The second is located inside the National Guard Recruitment Centre in the Barracks area next to the corpse of Knight Astlin.

The third is located at the the Revere satellite array next to Scribe Faris, at the top of one of the four non-central towers.

Once all three holotapes have been played, the player character will then have a quest marker appear at Recon Bunker Theta which is normally inaccessible. Once you have entered, you will be accosted by Paladin Brandis who will demand to know why you are there. If you inform him of the fate of the soldiers, he will allow you to loot the items in his home, which includes a Fusion core.

You then have the option of persuading him to rejoin the Brotherhood of Steel. You must pass three conversation checks and if any of them fail, he will remain where he is. If you succeed, you will find him aboard the The Prydwen where he will reward you with his gun.

Bugs

 * If the player character puts off completing this quest until after Paladin Danse has become a potential companion, they may be unable to turn the quest in as he will only offer companion dialogue options. However, after a period of time the mission turn in point will be transferred to Captain Kells, allowing for completion.
 * Captain Kells will give generic dialogue instead of allowing the player character to turn in the quest until after they've completed Show No Mercy for the Brotherhood of Steel.
 * Speaking to Brandis (or simply entering the National Guard Training Yard) may cause the player character to lose Fast Travel capability. Every time the map is opened, the same message will appear: "Fast Travel is currently unavailable from this location." This message appears anywhere, even if there are no enemies around, the player character is not overencumbered, and are not in a building.
 * If Brandis is spoken to before starting the first Brotherhood Quest (Fire Support), the quest will not require to return to Danse; it will simply be marked complete.
 * Failing to complete all speech challenges, but still convince Brandis to join the Brotherhood of Steel would still prompt you to Paladin Danse. Killing Brandis will give you the unique weapon, but still allow for you to turn in the quest to Paladin Danse for a double reward.