Fallout 3: Vault 87 Was the Birthplace of the Capital Wasteland's Super Mutants

gamerant.com:

Vault 87 is one of the most difficult locations to access in Fallout 3. However, the Lone Wanderer has no choice but to find a way in, as this vault contains an item necessary for furthering the main quest: the G.E.C.K.

That aside, this Fallout 3 vault has a long, gruesome history of scientific experimentation. The scientists within the facility were tasked by Vault-Tec with conducting heinous experiments on the unsuspecting residents. These scientific projects involved administering the Forced Evolutionary Virus into human test subjects; unsurprisingly, things didn’t go well.

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Vault 87 was built with both civilian living quarters and a medical wing. The latter was an extensive facility, complete with lab cubicles and workstations for the scientists who were assigned to the vault. This was unlike the other vaults in Fallout 3, in-line with the experiments Vault-Tec had planned for Vault 87.

Vault-Tec partnered with the US military to explore the effects of the Forced Evolutionary Virus, or FEV, on human subjects. To do this, they installed equipment like stasis chambers and plasma containment fields. They also assigned a scientist named Wayne Merrick to oversee what would be known as the Evolutionary Experimentation Program (EEP). Cut Fallout 3 content describes Merrick as “one of the brightest minds in the field of accelerated evolution,” which is likely why he was chosen for the job.

After Vault 87 was fully equipped with the necessary research tools, Vault-Tec let inhabitants in. None of them knew they were to become test subjects in the EEP, which isn’t surprising given Vault-Tec’s history. One by one, Merrick and his team picked off the residents and began experimenting on them.