O2 has reportedly won a lucrative contract to provide the Ministry of Defence (MoD) with 42,000 mobile connections in a deal said to be one of the largest of its kind in the public sector, with annual spend topping £5m.

According to Mobile News, O2 won the contract away from Vodafone, which has previously provided mobile connectivity services to the MoD for over 13 years, prior to the deal expiring late last year. The MoD employs over 56,000 staff across the three arms of the British Armed Forces.

The new deal, which will reportedly last four years, has been made in partnership with EE parent BT, which launched The Defence Fixed Telecommunications Service (DFTS) in 1997 with the UK government. The DFTS securely manages the MoDs communication needs across both fixed and mobile networks, through a partner operator, and has apparently saved the MoD over £800m to date in infrastructure costs.

While neither the MoD or any of the operators involved have commented on the deal, it is understood that O2s security was a major factor in the company securing the new deal. O2 was the first network to achieve government approved CAS(T) certification for voice and data services back in 2014, and reportedly spends around £1.5m a day to maintain network quality.

In the past few years, O2 has won nine out of 17 available central government contracts, and has overtaken Vodafone as the number one supplier to the public sector. The MoDs transition from Vodafone to O2 will take gradually, but is expected to take place by around Q3 2016.