Warp Knights

Raiders of the Immaterium
The Warp Knights are a third founding chapter of unknown origins. Led by Chapter Master Ortavian Rex they spend countless years in the immaterium at a time, waiting for the moment to strike. Equipped in outdated armour they are still a force to be reckoned with and will often unleash their entire chapter against their most hated foe, the Necrons. Ignoring all the Imperium commands the Warp Knights see no problem with viewing xenos as allies and have fought alongside Tau, Eldar and, rarely, even Ork warbands to destroy necron forces. A chosen few have even seen inside the webway.

Though not yet fully considered traitors (many of their actions are unknown even to the inquisition) they are shunned by the imperium they serve. The warp knights would rather fight alongside the dread legions of chaos and risk eternal damnation than lose a single world to the Necrons. Eschewing bikes and jump packs the warp knights prefer terminator armour and massed armoured infantry assaults. With all the time spent in the warp they undoubtedly lose equipment and suffer casualties. The Warp Knights will readily use weapons traded from the Eldar and any captured arms they find and are not above taking gene-seed from any Astartes bodies they find.

Standard Warp Knight tactics
A Warp Knight force will wait in the warp, the entire fleet ready to drop out at any moment. Coming out of warpspace they immediately deep strike in numerous Terminator squads followed by whole companies in drop pods and other xenos forms of transport, whichever will get them down first. The Infantry line will slowly but surely move forward with armour landed in by ThunderHawk. With this method they can strike at the slow reacting Necrons they often face and dispatch them before they are all fully awoken.