Grand Union, which triumphed in a pitch against undisclosed agencies, will create an online identity for the Army.
The Army currently runs a series of sites ranging from ArmyNet, its internal communications portal, to recruitment and individual regiment sites.
It is now expected to issue a brief to find an agency to advise it on digital strategy through COI.
Neither pitch will affect Publicis' hold on the above-the-line business.
The agency recently made digital a key part of its "Everest West Ridge" campaign, which saw soldiers film their attempt to climb to the summit of Mount Everest.
Grand Union was unavailable for comment. COI confirmed a strategy brief would be issued soon.