Ad Victoriam

Ad Victoriam is a Brotherhood of Steel main quest and achievement in Fallout 4.

Quick walkthrough
Speak to Proctor Ingram, plug in the Beryllium agitator and active the power transfer switch. Follow and defend Liberty Prime on its way to The Institute.

Bugs
While following Liberty Prime he may stop walking and not continue, make sure to regularly quicksave in case this happens. This can be fixed by shooting him (which won't cause him to become aggressive) or by fast travelling to C.I.T. ruins, or by fast travelling to the institute and completing Banished from the Institute.