Wars are testbeds for new technology. The Korean war saw jet fighters employed at scale for the first time. Israel pioneered the use of drones as radar decoys in its war with Egypt in 1973. And the Gulf war of 1991 was a coming-out party for gps-guided munitions. Russia’s invasion of Ukraine is the first time that two mature cyber-powers have fought each other over computer networks in wartime. The result is a lesson in the limits of cyber-power and the importance of having a sound defence.