BT is to provide NATO's Consultation, Command and Control Agency (NC3A) with a €47m (£39m) communications network that connects more than 70 of its locations.
NATO is a military alliance consisting of 28 member countries from North America and Europe. The NC3A is responsible for delivering technology in support of NATO's global operations.
The five-year deal includes the migration of NATO's existing infrastructure to BT Ethernet Connect, a network that BT says is designed for large organisations that require exclusive control over their IP architecture and want the freedom to evolve their infrastructure in their own way.
NC3A will also use BT's Ethernet Connect E-LINE service, which provides protected bandwidth for mission-critical applications between sites. BT will also supply NC3A with the hardware for a secure wide area network (WAN).
Georges D'hollander, general manager at NC3A, said that the deal supports NATO's vision of a more flexibile, future-proof infrastructure.
"Information and the ability to share it rapidly across a coalition plays a paramount role in 21st century operations as well as political decision-making. To underpin this we need a flexible, future-proof network."