Belly of the Beast

Belly of the Beast is a main quest in Fallout 76.

Quick walkthrough

 * Locate the following Brotherhood transponders using the Brotherhood emergency transponder radio station:
 * Atop an elevated guardpost southeast of Appalachian Antiques.
 * Next to a crashed Vertibird near AMS Corporate Headquarters.
 * Near the center of Survey Camp Alpha, sitting on a fortification.
 * On the roof of Drop Site V9.
 * In the final section of the Glassed Cavern near Elizabeth Taggerdy's corpse.
 * Collect Lieutenant Elizabeth Taggerdy's ID from her corpse.
 * Leave the glassed cavern and travel to Fort Defiance.
 * Use the ID card to access Paladin Taggerdy's terminal on the top floor. Reading the entry '[Ultimate Solution]' will complete the quest.

Detailed walkthrough
The quest begins right after Recruitment Blues is completed by reading the "[URGENT: Touchdown Recovery]" entry on Senior Knight Wilson's terminal in Fort Defiance. Monitoring the transponder signal strength via the Brotherhood emergency transponder radio station will allow the player character to locate five Brotherhood transponder beacons which are scattered around the Cranberry Bog. When a transponder is located, the player character must sync the transponder before they receive the approximate location of the next transponder. Replaying the last transmission alone will not update the quest marker.
 * Transponder 1 is located on the road between Fort Defiance and Watoga, southeast of Appalachian Antiques, at a small Brotherhood outpost overlooking Watoga.
 * Transponder 2 is located in Watoga, by the crashed Vertibot in front of AMS Corporate Headquarters on the east side of the city.
 * Transponder 3 is located at Survey Camp Alpha, southeast of Watoga.
 * Transponder 4 is located at Drop Site V9, on top of the bunker, dangerously close to Fissure site Prime.

Transponder 5 is located in the final section of the Glassed Cavern. The glassed cavern is a long, relatively linear dungeon, with only a few side tunnels diverging from the main path. It is usually occupied by Scorched, and may also contain mirelurk kings, fog crawlers, Protectrons or Eyebots. The transponder signal strength will fluctuate while the player character travels through the cavern, making it a poor indicator of whether or not one is going in the right direction. The cavern is full of deceased mirelurk sub-species, cave crickets and fog crawlers, that have been infected with the Scorched Plague along with broken Auto-Miners. Eventually the cavern reaches a point where it forks. Take the left fork and follow the rail tracks. At this point the transponder signal strength should stop fluctuating as much and begin climbing. A single wave of Scorched may spawn here to engage the player. (Note that pre-Wastelanders, multiple waves of enemies used to spawn at this point.)

The transponder is located on the northern side of a large cavern by Elizabeth Taggerdy's corpse. This cavern also contains several Scorched and a fissure, from which a scorchbeast emerges, which serves as the boss of the area. It can either be fought, which can prove to be tough, as it will never try to take flight and repeatedly use its shockwave attack to summon additional Scorched to aid it. Or the fight can be avoided by sneaking close to the eastern wall near the transponder. Regardless of which approach is chosen, sync the transponder and loot Taggerdy's corpse to retrieve her ID card. The cavern can then be exited by either using the elevator located in the final cavern or by simply fast travelling to another destination.

Return to Fort Defiance and travel to the top floor using the security elevator. Use the ID card to access Paladin Taggerdy's terminal on the top floor and read the entry "Ultimate Solution" to complete the quest and begin Uncle Sam.