A Lightning Arc is a Necron starship weapon system that is mounted on all known classes of Necron warship. Commonly mounted in batteries, Lightning Arcs use stored solar energy and, when activated, release it as a forest of living energy tendrils which envelop targets and probe for weaknesses.
Lightning Arcs act as the main weapon batteries for Necron ships, but are different from the equivalents used by the other starfaring species of the galaxy in that the arcs they fire are able to split up and guide themselves to their own targets, providing a mass-strike ability like no other known ship-based weapon. A Lightning Arc battery is usually able to cover all angles of approach except for the rear.
- Battlefleet Gothic Armada, pg. 73