The U.S. military operation targeting Iran‘s Fordow facility was 15 years in the making, according to Gen. Dan Caine, the chairman of the Joint Chiefs of Staff.

The Defense Threat Reduction Agency, known as DTRA, has been tracking the construction and development of the facility in the mountainous terrain since 2009. An officer Caine did not name was tasked with understanding and studying every aspect of the facility, and was later joined by a partner.