RAF Enigma
I started re-reading John Terraine's magisterial history of the RAF in WW2 "The Right of the Line". He describes how in 1934 a Wing Commander - O Lywood -, borrowed a commercial Enigma machine which had been bought by the Govt Cypher School in 1928 and effectively reverse engineered it so that by 1936 two "RAF Enigmas" were in trials. It was then renamed "Type-X" as people were starting to talk about it and they were worried about patent infringement(!!).
By 1938 it was being rolled out across the RAF and at high levels of Army communications and was used right through the war. The Navy refused to adopt it, which was a disaster as the Italians had pretty much broken UK naval codes during the Abyssinian crisis. The RN only realised they were compromised in mid-war when they could read the Naval Enigma .....
Oddly the Germans never managed to break the RAF or Army codes - it's not even known if they realised it was an Enigma based system....................