During the German Invasion of Poland in September 1939, key Cipher Bureau personnel were evacuated southeast and—after the Soviets invaded eastern Poland on 17 September—into Romania, on the way destroying their cryptological equipment and documentation. Eventually, crossing Yugoslavia and still-neutral Italy, they reached France. Some personnel of the Cipher Bureau's German section who had worked with Enigma, and most of the workers at the AVA Radio Company that had built Enigma doubles and cryptologic equipment for the German section, remained in Poland. Some were interrogated by the Gestapo, but no one gave away the secret of Polish mastery of Enigma decryption.