Google's pilot project with the Defense Department's Project Maven, an effort to identify objects in drone footage, has not been previously reported, but it was discussed widely within the company last week when information about the project was shared on an internal mailing list, according to sources who asked not to be named because they were not authorized to speak publicly about the project.

Some Google employees were outraged that the company would offer resources to the military for surveillance technology involved in drone operations, sources said, while others argued that the project raised important ethical questions about the development and use of machine learning.

Google's Eric Schmidt summed up the tech industry's concerns about collaborating with the Pentagon at a talk last fall. "There's a general concern in the tech community of somehow the military-industrial complex using their stuff to kill people incorrectly," he said.