MOSUL, Iraq (AP) — First the tiny drones buzz overhead to observe Iraqi soldiers. Then, the Islamic State group’s flying machines return to drop a small explosive device to sow panic among security forces — or deadlier still, to help guide a suicide car bomber to a target.

And the innovations are expected to keep coming since IS has been spending freely on technology, even as their fighters face intense pressure from coalition forces, according to Iraqi military officials.

The extremist group is hacking store-bought drones, using rigorous testing protocols and innovating tactics that mimic those used by U.S. unmanned aircraft to adapt to diminishing numbers of fighters and a battlefield that is increasingly difficult to navigate on the ground.

The Associated Press visited a warehouse this week in the Shura neighborhood, the largest drone workshop uncovered so far, and saw accounting spreadsheets with purchases totaling thousands of dollars a month for drone equipment. One receipt dated just a few months before the Mosul operation began recorded the purchase of wires, silicon, electrical plugs, cables, rotors and GoPro cameras. Other receipts logged in spreadsheets included food delivery orders of fried chicken, taxi fares and repair costs to the house’s hot water heater.

Scattered among the stacks of paper were bits and pieces of the drones themselves. Most were destroyed by IS as they retreated, Iraqi officers at the factory said. But pieces of styrofoam wings, fins and radio transmitters remained, piled up in the corners of the factory on a recent visit.

All the accounts were headed “board of development and military manufacturing,” some sub-headed “air observation division.” Handwritten notes instructed IS drone operators to write daily “mission reports” and monthly reports “about the challenges and difficulties you face as well.” In all, a half-dozen of the storehouses to make and modify the drones have been found recently in Mosul.

A cache of documents also obtained this month in a smaller makeshift factory by a researcher in Mosul, Iraq, indicates that the group is testing small drones, which are normally used as playthings, with deadly intent.

The researcher, Vera Mironova, is a labor economist by training and said her discovery of the drone paperwork — which includes lists in English and Arabic of parts and one file marked ‘Tool Kit’ that is a checklist of several dozen of the essentials — is a sign of what is essentially a program to let machines make up for a shortage in manpower. Items 1-5 were GoPro and chargers; battery cable; laptop; explosives; and devices.

Mironova, a fellow at Harvard University’s Kennedy School of Government, said the use of drones to both drop explosives and to direct more deadly payloads is an adaptation to the decrease in the number of attackers available. Early in the Mosul fighting, she said, suicide bombers tended to be deployed haphazardly more to frighten than to kill. But it didn’t take the group long to need a new approach.