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Much of the Grafton Steel mill's production and research occurred underground, in this portion of the mill. The work environment was noted to be uncomfortably hot and accidents were common, while employee suggestions went largely ignored by the management.
As part of Grafton Steel's war contract with the federal government, the mill was given a grant to pursue research into increasing the mill's steel yield, as well as developing new military-grade steel alloys.
Three projects were underway by the time of the Great War: Projects Phoenix, Adamantine, and Vulcan. Inspired by Garrahan Mining's excavator power armor, Phoenix focused on creating civilian power armor designed to withstand high temperatures in order to service machinery without shutting down production. It was the only project with material progress by the time of the Great War, with a finished prototype helmet. Adamantine was a provision by a military administrator for approving the grant, who requested the mill develop a new super-steel alloy while refusing to accept existing alternatives.
Vulcan aimed to boost the efficiency of the mill's steel forges, though its exact plan was still unknown. The grant also led to the installation of automated security within the Underground, as well as increased work hours for its employees.
Grafton Steel Underground is a linear complex explored in its entirety during the quest Fun and Games. It is a series of large areas connected by smaller hallways and tunnels, divided into three main sectors based on security keycards and passwords: Alpha, Bravo, and Charlie. The complex is filled with security robots of all types, ranging from Protectrons to Assaultrons, and even a sentry bot.
- Grafton Steel infiltrator's note - Note, given to the Vault Dweller by Ra-Ra during Fun and Games.
- Bravo sector security password - Password, found on consoles near the Bravo sector security terminals. It is just past the walkway above the automated turrets on a desk with a destroyed terminal.
- Grafton Steel sector Alpha keycard and sector Charlie keycard - Keycards, obtainable during Fun and Games. Used to access ID card readers throughout the facility. The sector Charlie keycard is given by Ra-Ra along with the infiltrator's note.
- Prototype steel mill paint - Found on the power armor chassis as a T-51 helmet, in the same side room.
- Power armor chassis - Found in a side room after the first assaultron spawn, only accessible during Fun and Games through dialogue with Ra-Ra if one has been nice to her.
- One respawning Nuka-Grape in a safe requiring 2+ hacking skill.
- Potential Vault-Tec bobblehead - On the ground level of the large room with the laser turrets, on a steel cabinet.
- Potential weapon mod plan - On a cabinet (or ground) in the southwest corner of the Bravo sector.