30mm cannon also: M230 chain gun
The cannon slung under the nose of an Apache. It fires shells about the thickness of a soft-drink can at roughly ten rounds a second. It is designed to destroy light vehicles, which is why its effect on people standing in a street is total.
AGM-114 Hellfire also: Hellfire
An air-to-ground missile carried by the Apache, built to kill tanks. Three were fired into a partly built residential block in the third engagement of 12 July 2007.
AH-64 Apache also: attack helicopter
The US Army's main attack helicopter. It carries a 30mm chain gun under the nose, rockets, and Hellfire missiles. Its targeting camera and the gun are slaved together, so the recording you see is roughly where the gun is pointed. Both aircraft over the district that morning were Apaches.
Air weapons team also: AWT
A pair of attack helicopters working together, one leading and one covering. Crazyhorse 1-8 and 1-9 were an air weapons team.
AR 15-6 investigation also: 15-6
A US Army administrative investigation, named after the regulation that governs it. It is an internal fact-finding exercise for commanders, not a criminal inquiry, and it cannot itself charge anyone. The 2007 investigation into this airstrike was a 15-6.
Callsign
The radio name of an aircraft, unit or person. Crazyhorse 1-8 identifies a particular aircraft on a particular day, not a permanent name, which is one reason the crew have never been publicly identified from the recording alone.
Collateral damage
The military term for harm to civilians or civilian property that was not the object of an attack. It is a legal category, not an excuse: harm can be lawful collateral damage, or it can be disproportionate and unlawful, and the difference is what lawyers argue about.
Court-martial
A military criminal trial. Chelsea Manning was tried by court-martial in 2013. No member of the aircrew was ever charged, so no court-martial ever examined the airstrike itself.
Declared hostile
A status that lets forces engage a person or group on sight, without waiting for them to act. It is a significant step, and it shifts the question from what someone is doing to what they have been assessed to be.
Distinction
The rule in the law of armed conflict that forces must tell civilians apart from fighters and may only deliberately attack fighters. The first engagement is judged against this rule.
Espionage Act also: 18 U.S.C. §793
A 1917 US law originally aimed at spying, now the main tool used against people who give classified information to the press. It gives a defendant almost no room to argue that a disclosure served the public. Manning was convicted under it; Assange was charged under it.
Freedom of Information Act also: FOIA
The US law that lets anyone request government records. Reuters used it for almost three years to try to obtain this footage and never received it. That failure is a large part of why the leak mattered.
Gun camera also: TADS footage
The recording made by an aircraft's targeting sight. It is grainy, black and white, narrow, and shot from far away, which is exactly why two people can watch the same clip and honestly see different things.
New Baghdad also: Al-Amin al-Thaniyah, Al-Amin
The district of eastern Baghdad where the airstrike happened. A dense, mostly residential area that saw heavy fighting in 2007. It is often written as New Baghdad in English reporting and as Al-Amin al-Thaniyah locally.
Positive identification also: PID
The requirement to be reasonably certain that a target is a lawful one before firing. Almost every argument about the first burst of fire is really an argument about whether positive identification was actually achieved, or only asserted.
Proportionality
The rule that expected civilian harm must not be excessive compared with the concrete military advantage expected. Firing three missiles into a building in a residential street is the part of that morning most often tested against this rule.
Redaction
Removing names and details from a document before publishing it, to protect people who could be harmed. How much redaction WikiLeaks did, and when, is one of the sharpest disagreements in the later part of this story.
RPG also: rocket-propelled grenade
A shoulder-fired anti-armour weapon, common on both sides of the fighting in Iraq. At least one man in the street appears to be carrying one. A long camera lens on a shoulder and an RPG tube on a shoulder look similar through a gunsight at that distance, and that resemblance sits at the centre of this case.
Rules of engagement also: ROE
The orders that tell a soldier when they may use force, who they may use it against, and what they must do first. They are not the law of war, but a commander's application of it to one place at one time. The 2007 rules in Baghdad are the standard the Army measured this crew against.
The surge
The 2007 increase of roughly 20,000 additional US troops in Iraq, most of them sent into Baghdad, with orders to hold ground rather than patrol from large bases. It is why an American infantry company was fighting inside this district that summer.
Whistleblower
Someone inside an organisation who reveals wrongdoing. Whether the word fits Chelsea Manning is contested: supporters say it plainly does, the prosecution's position was that the scale of the disclosure put it outside any such protection. US law offers almost no whistleblower defence for classified material given to the press.
Wounded and those who collect them
Under the Geneva Conventions the wounded who are out of the fight are protected, and so, in general, are people who come to collect them. This is the rule the engagement on the van runs into, and it is why that phase is treated separately from the first burst.