All Factions;
Armour is five-tiered, with minor material improvements between each tier. Armour steadily improves and slightly reduces injuries taken.

Limbs are five-tiered, with minor toughness improvements between each tier. WoundLimit progression is much slower, as Marine factions are already extremely tough.

Wounds are triple-tiered; basic/stock wound, and two higher tiers that reduce damage from burst/emission. The second tier is applied to Toughness 2/3 actors; the third to Toughness 4/5.

All faction leaders (Sergeants) start with Assault Packs.

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Ultramarines start with Sergeant Titus and get two Scouts and two Marines.
Brothers Aeschylus and Agathon, and Neophytes Zopyros and Hypatos, all gain Assault Packs at Toughness 3.

Ultramarines get easier access to certain higher-tech equipment, and a slight discount on all weapons.

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Dark Angels start with Sergeant Corax and get two Scouts and two Marines.
Brothers Corvus and Albus gain Assault Packs at Toughness 2.
Neophytes Bennetti and Enca gain Assault Packs at Toughness 3.

Dark Angels get a gold/data discount on all flamethrowers, and can use data to unlock the Heavy Flamer.

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Blood Angels start with Sergeant Pietro and get a Scout and three Marines.
Neophyte Delmonte gains an Assault Pack at Toughness 2, and increased innate regeneration at Toughness 4.
Brothers Pirro, Jago and Tasso gain Assault Packs and increased innate regeneration at Toughness 3.
Sergeant Pietro gains increased innate regeneration at Toughness 3.

Blood Angels get a gold/data discount on melee weapons and medikits, and can use data to unlock the Power Sword.

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Black Templars start with Sergeant Konstantin and get four Marines. They are tougher than all other Space Marine factions;
Their armour starts at Mk II Ceramite and reaches Mk V at Toughess 4, rather than 5.
They start with second-tier Wounds and upgrade to third-tier at Toughness 3.

Brothers Seppel, Matthias, Wolfram and Ignatz all gain Assault Packs at Toughness 3.

Black Templars have get a gold/data discount on high-tech equipment such as plasma guns, and can use data to unlock the Bolter CombiPlasma and Plasma Cannon.

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Space Wolves start with Sergeant Farkas. Brothers Vilkas, Qurd, Maikan and Varg are all little unique compared to other factions;
At Toughness 1, the Space Wolf is pretty much a normal Wolf Scout.
At Toughness 2, the Space Wolf gains a Mk II Ceramite Aquila Breastplate.
At Toughness 3, the Space Wolf gains Mk II Ceramite armoured legs and an Assault Pack.
At Toughness 4, the Space Wolf gains faster innate regen (compared to scout tier), Mk III Ceramite armoured arms, and legs are upgraded to Mk III Ceramite.
At Toughness 5, the Space Wolf gains a full Aquila helmet, and all armour is upgraded straight to Mk V Ceramite.

This is _on top of_ other progressive durability bonuses gained through Toughness progression.

Space Wolves have a significant gold/data discount for melee/close combat weapons and can use data to Power Axes. They also get a small data discount on standard Bolt weapons.
Unfortunately, they have a much harder time getting complex, high-tech weaponry.