In 2017, Google partnered with the Pentagon on Project Maven, using AI to analyze drone surveillance footage and identify targets. The contract was kept secret until exposed by Gizmodo in March 2018. Over 4,000 Google employees signed a letter demanding Google exit 'the business of war,' and at least 12 resigned in protest. Google eventually let the contract expire in March 2019 and published AI ethics principles prohibiting weapons development. Palantir subsequently took over the contract.