Battle of Project Purity The Battle of Project Purity was a battle fought between the Capital Wasteland Brotherhood of Steel and the Enclave in the year 2277 . The Brotherhood of Steel aimed to reclaim the Jefferson Memorial from the Enclave in order to stop them using the purifier for Project Purity for their own plans , and to activate it themselves and distribute fresh , pure water to the citizens of the Capital Wasteland . Prelude . After entering Vault 87 , the Lone Wanderer retrieved a G . E . C . K . , but was captured on the way out by two Enclave soldiers and Colonel Autumn , who was thought to be dead at the scene . With the G . E . C . K . confiscated , the Lone Wanderer was put onboard a Vertibird and flown out to the Enclave ' s headquarters at Raven Rock . At Raven Rock , after refusing to give the Enclave the code for the purifier and having a personal audience and meeting with the President John Henry Eden , the Lone Wanderer was handed a vial of modified Forced Evolutionary Virus , and ordered to plant it into the purifier upon activating it . The aftermath of these events are currently unknown , however the Lone Wanderer escaped Raven Rock after a schism in the ranks between those loyal to Autumn and wanting the Lone Wanderer dead , and those loyal to Eden . The Lone Wanderer then traveled back to the Citadel and informed the Brotherhood of the situation . Preparation for attack . When the Lone Wanderer arrived at the Citadel , there was a debate between Sentinel Sarah Lyons with her squad , and Owyn Lyons with Senior Scribe Reginald Rothchild , over whether to attack and reclaim the Memorial from the Enclave . The Lone Wanderer gave the Elder information shaping the discussion , as well as the fact that the G . E . C . K . was lost to the Enclave , resulting in him ordering Liberty Prime to be launched and the Jefferson Memorial to be attacked . Liberty Prime was carried by crane out of the Citadel walls and set down near the Arlington Memorial bridge . The Lyons ' Pride and the Lone Wanderer , who was now a member of the squad , followed Prime outside . Battle . Immediately after Prime was set down outside the Citadel , the Enclave sent barrages of artillery from the Memorial at the Pride , and sent waves of Vertibirds to eliminate them . However , neither of these measures were any use , due to Prime taking almost a hundred direct hits from artillery and enduring no damage whatsoever , and his head lasers dispatching Vertibirds with ease . The Brotherhood set up snipers along the beginning of the Arlington Memorial bridge . With his ability to disarm photonic resonance barriers , Liberty Prime led the Pride along the Arlington Memorial bridge , slaughtering hordes of Enclave squads with his head lasers and tactical nukes . They passed the irradiated metro with the very same outcome . Once Prime set foot on the Memorial grounds , the Pride stayed outside and assisted Prime in eliminating a wave of around thirty Enclave soldiers from the higher scaffolding of the Memorial to act as a distraction while Sentinel Lyons and the Lone Wanderer broke into the facility and fought their way to the rotunda . Once they reached the rotunda , they were confronted by Autumn and two of his guards . The outcome of this is unknown , however , after Autumn was dealt with , Madison Li sent a message via intercom to the Memorial , informing them that pressure was building up in the purifier ' s holding tanks after massive damage during the fighting , some of which seemed to be accidental , and others sabotage . The pressure had to be released by activating the purifier , or else the facility could explode . However , the purifier activation hub was flooded with lethal levels of radiation . Lyons and the Lone Wanderer or their companions were forced to decide who would activate the purifier . Once they decided , the purifier was activated and the water was distributed across the wasteland . The Lone Wanderer didn ' t act upon Eden ' s wishes to sabotage the purifier with the modified FEV . This is indicated by a comment by Deacon in " Fallout 4 " Aftermath . Both Sarah Lyons and the Lone Wanderer were knocked into comas and taken to the Citadel for treatment . Meanwhile , Scribe Bigsley set up the delivery center at the Jefferson Memorial , and took charge of the water deliveries across the region . Rivet City was enlisted to support these efforts and take charge of water caravan deliveries , led by Officer Lepelletier . If the Lone Wanderer did not , Liberty Prime was sent to destroy Raven Rock . The Enclave retreated to Adams Air Force Base . The Lone Wanderer awakened two weeks after the battle , beginning the events of " Broken Steel " . Appearances . The Battle of Project Purity appears only in " Fallout 3 " and is mentioned in its add - on " Broken Steel " .