The cause of the CH-47 crash is still under investigation, according to the coalition. Which weapon — or weapons — were responsible is not yet known. Several publications claim an insurgent Rocket-Propelled Grenade struck the helicopter. One Army insider who spoke to Danger Room went a step further, claiming that the rocket was, in fact, a special improvised model. A chopper-killer, if you will.

The so-called “Improvised Rocket-Assisted Mortar” made its debut in Iraq in 2008, although not in attacks on aircraft. IRAMs combine traditional tube mortars with rocket boosters and, in many cases, remote triggers, allowing insurgents to fire them from a distance.

IRAMs have killed several U.S. troops in Iraq over the years; in June, the weapons killed six Americans. but haven’t factored heavily in the Afghanistan fighting. The weapon’s appearance in Wardak, if confirmed, could be proof of Afghan insurgents’ continued ability to adapt and innovate despite mounting losses.

Improvised rockets are notoriously inaccurate. But with bigger warheads than shoulder-fired RPGs, IRAMs are potentially much more destructive when they do hit.