Specialist
From Exterminatus Manual
++Chaos Legions++
Specialist Marine (Specialist)
Overview
Most tactical squads contain one marine who is trained in the use of support weapons. These are often rare, difficult to use or otherwise specialised in their function. The 'Specialist' class in Exterminatus is a Renegade marine who has traded in his Boltgun for a Flamer or Plasmagun.
Weapons
Specialist marines get a choice of two selections of waregear. The first option is the Plasmagun a rifle type weapon that is good against armour. The second option is the shorter ranged Flamer that is better against groups of enemies. Specilists also carry a knife and backup bolt pistol.
Tactics
The longer you hold the attack key of the plasmagun the more powerful the shot will be. Flamers are good at area denial, bathe the ground in flames to burn your enemies where they stand or flee.
40K vs Exterminatus
Meltaguns have been relegated to Raptors as they are able to make better use of such a short ranged weapon.