A US army Apache helicopter fires a missile during training near Bagram October 22, 2002. Reuters An ISIS-made guide for downing American military helicopters briefly hit Twitter last month, before the responsible account was suspended.

A US-led coalition of western and regional players has been bombing ISIS targets for weeks in an effort to check the militant group's lightning expansion. The American-led campaign has been almost entirely waged from the air, and the ISIS guide goes into fairly technical detail on how to shoot down enemy aircraft with a shoulder-fired man-portable air-defense system, or MANPADS.

Translated excerpts of the original Arabic-language guide posted on New York Times journalist CJ Chivers's website call for the destruction of Apache helicopters, specifically, to "cause a disaster to the foes and destroy their arrogance."

The guide is full of tips for effective anti-helicopter warfare. It cautions militants to take no more than ten seconds to fire their missiles, in order to go unnoticed by the Apaches' "detecting devices." It also advises fighters to fire from the ground in a way that "prevents the appearance of dust following launching." It even tells them to create decoy launch sites, then booby-trap the area with explosives in case allied ground troops arrive to investigate the attack.

Other methods to maximize the chance of success include targeting an Apache while its crew-members are busy firing their own weapons, since a distracted pilot is less likely to have the awareness needed to dodge an oncoming missile. And if two MANPADS are available, it's apparently best to have them fire at a ten-second interval, from vantage points 200 to 500 meters apart.

These tactics fit into a larger strategy for maximizing casualties. Fighters are advised to wait for the arrival of further helicopters after an Apache is attacked and attempt to down those as well — the guide says to have 4 to 6 missiles ready for each engagement, since the overall objective is to shoot down more than one aicraft.

ISIS fighters should also have a sniper ready to pick off survivors. They are encouraged to shoot down helicopters in a way that ensures the deaths of as much of the crew as possible: MANPADS operators shouldn't fire more than "1500 Meters from the helicopter’s scope line, so we may not give the pilot the chance to escape after shooting the missile."

The guide includes worryingly specific operational instructions that suggest the author has some first-hand familiarity or even expertise with using MANPADS on the battlefield. ISIS has anti-aircraft specialists who may be spreading their knowledge among the group's ever-burgeoning ranks.

And they're creating a battlefield doctrine that reflects the group's cruelty, instructing fighters to wage war in as deadly and destructive a way as possible.