Google has confirmed that it is allowing the Pentagon to use some of its image recognition technologies as part of a military project.
The disclosure follows a report by Gizmodo, which said the artificial intelligence tech was being used to analyse drone footage.
The news site said that many of the search giant's workers only learned of the collaboration last week via internal emails.
It added that some were "outraged".
A spokeswoman for Google said that the tie-up involved the provision of software tools to let the US Department of Defense (DoD) make use of its TensorFlow machine learning code.
"The technology flags images for human review, and is for non-offensive uses only," she added.
"Military use of machine learning naturally raises valid concerns.
"We're actively discussing this important topic internally and with others as we continue to develop policies and safeguards around the development and use of our machine learning technologies."
Although Google's former chairman Eric Schmidt became an advisor to the Pentagon in 2016, the firm has otherwise been cautious about being linked to the US military.
It previously pulled one of its robots from a Pentagon-organised competition, despite it being the favourite to win, in part because of such concerns.
Data glut
Gizmodo identified the drone initiative involved as being Project Maven - a scheme announced last July to use computer algorithms to identify objects of concern from "massive amounts of moving or still imagery".
Image captionThe MQ-9 Reaper drone can fly as high as 50,000ft (15,240m) and has a range of 1,150 miles (1,850km)
The idea is to focus human efforts on sections of footage flagged for further analysis and avoid them having them having to wade through all the other hours of recorded material.
The DoD said that its immediate focus would be 38 classes of objects related to the fight against the Islamic State group in Iraq and Syria.
"There is no 'black box' that delivers the AI system the government needs, at least not now," said Colonel Drew Cukor at the time.
"The only way to do that is with commercial partners alongside us."
Google declined to discuss its involvement further.
But the BBC understands that the algorithms it has shared were not designed for face detection, but were instead developed to identify generic objects including cars, birds and trees. It is believed that they are not being used to fly or otherwise operate the drones themselves.
Google is not the only US firm to be involved.
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