The Torque Bow is a weapon used by the Locust elite Theron Guards.
The weapon is used by holding the trigger for a while to get the desired trajectory for the Torque missile / bolt, leaving the trigger results in the missile being shot. The longer you hold the trigger, the faster and straighter the missile lauches.
It is extremely deadly for the fact the one shot can kill you no matter where it hits, since it explodes after sticking to you. If a torque bow is not fuly charged, the bolt doesn't stick but it still explodes and enemies in close proximity will either get severe damages or will die depending upon their distance from the blast. It is extremely fast and unavoidable when it is fully charged, unlike say, a frag grenade.
In multiplayer it is possible to kill enemies with a headshot using this weapon, even if it is a sticky missile. However the missile has to be fully charged to get the velocity required for a headshot.
This weapon however is not without its flaws, since it takes a very long time to reload and carries only 12 bolts at a given time.
