The new guidance for the department came in a memorandum signed by Deputy Defense Secretary Kathleen H. Hicks.
"In areas of substantial or high community transmission, DOD requires all service members, federal employees, onsite contractor employees and visitors, regardless of vaccination status, to wear a mask in an indoor setting in installations and other facilities owned, leased or otherwise controlled by DOD," the memorandum read.
The memo also says that those who have not been vaccinated will need to continue to wear masks, as they have been required to do all along.
DOD installations are also being asked to post signage and update their websites to let visitors know of mask policies in place at those locations.
CDC guidance issued July 27 recommends that even individuals who have been vaccinated against COVID-19 start wearing a mask again while indoors if they are in an area of "substantial or high transmission."
"To maximize protection from the Delta variant and prevent possibly spreading it to others, wear a mask indoors in public if you are in an area of substantial or high transmission," the CDC recommends.
Information about areas of the country that are most at risk for transmission can be found on the CDC website.