His Angels of Death
A Space Marine (Astartes) is not a human in a suit. They are biologically enhanced weapons of war. * Height: 7-8 feet. * Weight: 500-1,000 lbs (unnarmored). * Reaction Time: Nanoseconds.
The Survival Odds
For a Guardsman, the life expectancy is 15 hours. For a Space Marine, it is centuries. They heal instantly (Larraman's Organ), breathe poison (Multi-lung), and can eat rocks (Preomnor). However, they are sent into the worst hellscapes imaginable. If a Marine dies, it's usually because something truly horrific killed him.
Armor Save
In the tabletop game, Marines rely on their 3+ Armor Save and 4+ Invulnerable Save (Iron Halo). In lore, their Ceramite plate can tank tank shells.