Operation: Sunburst

 was a military conflict in 2276.

Prelude
The Mojave chapter of the Brotherhood of Steel, as part of a wider conflict, would still be fighting the NCR as late as 2274. After establishing a base at Helios One, the Mojave Brotherhood soon found themselves at odds with the NCR and its growing power in the region. In 2274, the NCR had officially set up a regional military base at Camp McCarran. With a main base now set up, the NCR soon set its sights on the HELIOS One solar plant. Elijah, still believing that the plant contained an unprecedented military advantage, refused to leave the plant, and forced the paladins to continue defending it.

Battle
In 2276, NCR forces attempted to take HELIOS One. Although Head Paladin McNamara pleaded Elder Elijah to abandon the base and save the lives of the men, Elijah held fast, insisting that "something was almost ready", likely referring to the ARCHIMEDES weapon system that would guarantee victory. Salvation never came, however, and one day, Elijah simply disappeared into the wastes, gaining nothing at the cost of many lives. McNamara wasted no time in gathering the survivors and fleeing, leaving HELIOS to the NCR, but not before activating the plant's long-dormant security systems and crippling its power output.

Aftermath
The Brotherhood, now under Elder McNamara, fled to Hidden Valley, where they remained until at least 2281. Elijah set up an outpost at an abandoned Brotherhood of Steel bunker, and later set off to the Big Empty in search of technology to eradicate the NCR.

Since the Brotherhood's defeat, Elder McNamara had restricted activity outside the bunker to occasional reconnaissance missions and high-value raids. All operations take place at night, and engagement of NCR forces is strictly forbidden. Though the Brotherhood's ascetic lifestyle has prepared its members for a sequestered existence better than most, the passivity of the current situation has proved highly stressful.

The NCR held the power plant, but were unable to get it up and running. Its lack of a proper power output later made it a low-priority target for Caesar's Legion.

Appearances
Operation: Sunburst is mentioned in Fallout: New Vegas.