The Ministry of Defence (MoD) has awarded the Atlas Consortium, led by HP, an $890m contract as part of the Defence Information Infrastructure (DII) programme.
The contract work will aim to "improve global collaboration and communication between MoD and its allies".
The contract, called Increment 3a, is the next phase of the DII.
It will see Atlas providing 42,000 computer terminals, which will operate in the "restricted and secret" domains. The new equipment will apparently replace "outdated and expensive legacy systems".
The terminals will support 60,000 employees in the Royal Air Force, Joint Helicopter Command and other MoD locations.
The Atlas consortium also includes Fujitsu, EADS Defence and Security Systems, General Dynamics and Logica.
Huw Owen, chief executive officer, ATLAS Consortium and vice president, HP Enterprise Services Defence and Security in the UK, said: "It is critical to national defence that the MoD and its allies have highly secure and real-time global access to the information they need."
DII is the largest defence IT programme of its type in the world. When delivered in full, IT implemented under the project will provide services to around 300,000 users at some 2,000 locations worldwide.