Heavy
From Exterminatus Manual
Heavy Weapons Marine (Heavy)
http://www.40ksource.com/gallery/Imperial%20Player%20Models/HeavyMarine.jpg
Overview
A heavy weapons operative makes up the final component of most tactical squads. Using the large, heavy, awesomely powerful weapons to support his squad the 'Heavy' class is the pinnacle of the imperial classes, able to blast his way though hoards of foes with relative ease. All that fire power comes at a price, the mass of his weapon reduces heavy weapons marines to a plodding pace.
Heavies can be recognised by their extended backpacks, weighted boots and optical targeters, not to mention their massive guns.
Weapons
Heavy marines go into battle armed with an awesomely powerful Heavy Bolter, backed up by a Bolt Pistol side-arm and a Knife for when things get messy.
Tactics
The heavy bolter is the pinnacle of the Bolt Weapons development, with it you can lay down a sustained, hail of deadly fire, even at long range. Even the biggest nasties out there bow down before the might of the heavy bolter. The one small downside of all this awesomeness is the extra mass of this chunky gun and it's ammunition tends to make Heavy marines rather slower than their squad mates, so don't rely on being able to sprint out of trouble.
