The Defense Department, owner of 470,000 BlackBerrys, is distancing itself from the struggling vendor while moving ahead with construction of a departmentwide app store and a system for securing all mobile devices, including the latest iPhones, iPads, and Samsung smartphones and tablets.

Just two months ago, when BlackBerry announced the company would radically curtail commercial sales, Pentagon officials said their business partnership remained unaffected. At the time, Defense's technology support agency was readying networks with software to handle tens of thousands of BlackBerry Z10 and Q10 smartphones.

Last week, BlackBerry called off a tentative buyout and fired Chief Executive Officer Thorsten Heins, heightening uncertainty about the future of the company, which has seen its market share plummet in recent years as consumers embraced more user-friendly devices that run on operating systems built by Apple and Google.

For now, Defense's mobile security strategy primarily depends on BlackBerry. The Pentagon has granted only BlackBerry 10 phones and Playbook tablets an "authority to operate," or ATO -- not Android, Apple or any other device lines. Consumer smartphones and tablets must have an ATO to hook up to Defense networks.

(Related: Blackberry Bets Big on the Defense Department)

But there is a contingency plan at the Pentagon, should BlackBerry phones go the way of Betamax VCRs.

A 2012 strategy to transition personnel from PCs to smartphones and tablets did not favor any one device maker, Defense officials noted on Thursday. "This multi-vendor, device-agnostic approach minimizes the impact of [a] single vendor to our current operations," Pentagon spokesman Lt. Col. Damien Pickart said.

Implementation of the strategy centers on a "mobile device management" system to track handhelds that touch military networks so that they do not compromise military information or corrupt Defense systems.

"DoD's mobility strategy and commercial mobile device implementation plan includes reliance on multiple vendors to support its mobile communications needs," Pickart said.

The mobile security management system is in the early stages of development. It will undergo a limited pilot, or reach "initial operating capacity," by Dec. 31, Pickart said.

The Pentagon anticipates connecting 300,000 approved government-issued consumer devices by 2016.