The M136 anti-tank (AT4) launcher is one of the rarest and least useful weapons in DayZ. When equipped, it takes the place of the player's backpack. It can only be found in the barracks at the northwest airfield.
Designed entirely for removing armored targets and destroying small structures, the M136 Rocket is incredibly hard to come by, and when it is found players will often stockpile them in vehicles.
While it does a tremendous amount of damage, it's only dealt in a small radius due to the strict anti-vehicle design of the launcher. The surprisingly low audible range is offset by it's high visibility, which likely to attract any bandits in the area - much more accurately than sound alone would.