Complex sentence: It is believed that the Combined Cipher Machine was never broken by the Axis, although a British test cryptanalytic attack made considerable progress, the results were far worse than against the Enigma, due to the increased complexity of the system and the low levels of traffic.
Split into simpler sentences: It is believed that the Combined Cipher Machine was never broken by the Axis. Although a British test cryptanalytic attack made considerable progress, the results were far worse than against the Enigma, due to the increased complexity of the system and the low levels of traffic.