Russians at Tannenberg — Surely Nobody Is Listening

Russians at Tannenberg: ‘Surely nobody is listening’ / ‘Transmit everything’
German headquarters: ‘You hearing this?’ / ‘Every word’

The Battle of Tannenberg (1914). The Russians sent all their radio messages in the clear — no encryption. The Germans listened to everything. Result: one of the most decisive German victories of WWI. OPSEC matters.