In June 2017 the United Kingdom awarded a £260 million contract to fit Mode 5 Identification Friend or Foe equipment to more than 350 units already in service, and between 2024 and 2026 its Ministry of Defence published notices for interim support and for new Mode 5 sets and spares. European rearmament is usually measured through platforms, weapons, sensors, production capacity and contract values. Cooperative combat identification exposes a different constraint. A force may own an interrogator or a transponder, may have installed it on an aircraft, ship or air-defence system, and may still not possess a fully assured coalition capability. The military output depends on the behaviour of the equipment after integration, the approved configuration of the host platform, independent test evidence, access to cryptographic arrangements, national and allied certification, and the capacity to preserve that approved state as hardware, firmware and software change. IFF Mode 5 is therefore a useful test of how European procurement becomes operational capability, because the decisive object is not an electronic box but a continuously controlled configuration whose acceptability must extend beyond the purchasing organisation to the allied forces that rely on the identification result. The open question is which part of that chain, manufacture or assurance, sets the pace at which European spending becomes usable capability.