Helicopters are encoutered only in The Operative: No One Lives Forever missions Rescue Attempt and A Very Large Explosion. Helicopters are capable of taking a great deal of damage before going down. They are also capable of dealing a great deal of damage, as they are equipped with a minigun and a paratrooper on board will shoot at you with its Hampton MPL 9mm SMG. It's best countered with assault rifles or SMG's, although you need at least 2 clips to take a helicopter down.