Microwave photonics occupies an unusual position in Europe’s defence-electronics base. The underlying proposition is technically established: radio-frequency signals can be generated, distributed, filtered, delayed, converted and combined in the optical domain, allowing functions that become increasingly difficult to perform electronically as instantaneous bandwidth, carrier frequency and array complexity rise. The defence question is narrower and more demanding. A photonic circuit that performs one RF function in a laboratory is not yet a radar receiver, an electronic-support payload or a production-ready subsystem. Deployability depends on the complete chain around the circuit: lasers and modulators, photodetectors and amplifiers, RF interfaces, packaging, control electronics, thermal management, calibration, software, environmental verification, configuration control, design rights and an industrial route that can reproduce the same qualified performance. Europe already possesses important parts of that chain. The strategic issue is whether they can be joined under sufficiently durable European control to support modification, manufacture, qualification and sustainment, rather than producing a sequence of technically successful but programme-bounded demonstrations.