Gas

New York Times:

The helicopter was hovering over a Baghdad checkpoint into the Green Zone, one typically crowded with cars, Iraqi civilians and United States military personnel.

Suddenly, on that May day in 2005, the copter dropped CS gas, a riot-control substance the American military in Iraq can use only under the strictest conditions and with the approval of top military commanders. An armored vehicle on the ground also released the gas, temporarily blinding drivers, passers-by and at least 10 American soldiers operating the checkpoint.

“This was decidedly uncool and very, very dangerous,” Capt. Kincy Clark of the Army, the senior officer at the scene, wrote later that day. “It’s not a good thing to cause soldiers who are standing guard against car bombs, snipers and suicide bombers to cover their faces, choke, cough and otherwise degrade our awareness.”

Both the helicopter and the vehicle involved in the incident at the Assassins’ Gate checkpoint were not from the United States military, but were part of a convoy operated by Blackwater Worldwide, the private security contractor that is under scrutiny for its role in a series of violent episodes in Iraq, including a September shooting in downtown Baghdad that left 17 Iraqis dead.