Research in Motion said the US Department of Defense (DoD) approved six models of the company's BlackBerry 7 smartphones for use on its networks.
The approval means RIM's single largest customer can upgrade to the Canadian smartphone maker's latest devices.
RIM's BlackBerry phones have long been used by army and other defense department personnel, but each new version of the device must be tested before it can be approved for use in sensitive roles where a data breach could endanger national security.
Last year, the US Army introduced new applications and capabilities, such as Near Field Communications and voice activated universal search, for its BlackBerry users, RIM said in a statement.
The BlackBerry -- criticised as outdated and outpaced in a field of touch-based devices -- is used by US President Barack Obama, who owns a modified and tightly-controlled model of the smartphone.
(Reporting by Abhiram Nandakumar in Bangalore; Editing by Viraj Nair)