Rules3

And They Shall Know No Fear. The oldest and surest of the Astartes gifts: a battle-brother does not break. This rule is always in force. A fighter with it can never be Pinned by incoming fire, standing where a mortal soldier would throw himself flat. He automatically passes any Nerve test he is called to make, holding steady while lesser warriors rout around him. And once each round, should he be knocked Prone, he may Stand Up for free rather than spending an action to do so. Together these make the Marine a warrior who fights on through fire, terror and wounds that would shatter the will of anything less than transhuman — the durability of the Adeptus Astartes carried not in his armour but in his unbreakable mind.

Astartes Physiology. Beneath the plate a battle-brother is barely recognisable as a man. Two hearts, a lattice of grafted organs, ossified bone and skin cured against fire and blade make him a creature no unmodified human can match. So the line Marine stands at Toughness 5 with three Wounds, able to take blows that would kill a mortal outright and keep fighting. The Scout, whose implants are not yet complete, is the one exception, fielding the lighter Toughness 4 and two Wounds of a brother still in the making. The strength of a Chapter is written into its warriors' flesh: the body endures what the enemy cannot overcome.

Promethean Endurance: the mark of the forge-tempered body, borne by every living son of Vulkan. This fighter has a Feel No Pain 6+ save — after every other save has failed and a wound would be taken, roll a D6, and on a 6 the wound is ignored. The endurance is inherent, free and universal: the neophyte Scout carries it as surely as the Chapter Master, and it needs no purchase and no upkeep. It is the tempering of the flesh, not a device, so the revered war-engines take no part in it — a Dreadnought is a machine-tomb, not a body to steel. On everything that still lives, though, it is the quiet floor beneath the whole slow advance: the reason a Salamanders line grinds forward through punishment that would scatter a mortal squad, and the reason it so rarely falls.