But the Soviets knew that Tunny was broken, because Cairncross passed it to them, GCHQ knew this. The Russians weren't stupid - it was very clear that the Brits

But the Soviets knew that Tunny was broken, because Cairncross passed it to them, GCHQ knew this. The Russians weren't stupid - it was very clear that the Brits could read SS cipher traffic, the SS used Lorenz. I have read (but can't find it) that the Soviets used captured Lorenz.. but it is odd.