Bolter Drill Imperial Fists models can re-roll all To Hit rolls of 1 made with bolt pistols, boltguns, storm bolters, heavy bolters, and combi-weapons that are firing as boltguns. This rule also applies to models firing hellfire, kraken, vengeance, or dragonfire rounds.
Siege Masters Imperial Fists models can re-roll armour penetration rolls against buildings that do not result in a glancing or penetrating hit, and add 1 to the result when rolling on the Building Damage table. In addition, imperial Fists, Devastator Squads and Centurion Devestator Squads have the Tank Hunters special rule.