1.The author talks about the use of relays for the inversion and the transposition circuits. It was only the T52C and E machines that used relays for these circuits. The other machines, T52A/B and D, used the cam contacts directly on each coding wheel.
2.It is not entirely clear what the author has in mind here. The number of combinations given by the author, 2 612 736 000, does not appear to refer to the T52A/B machine. Gösta Borelius has not been able to find this number in the available FRA documents. As the author talks about the transposition relays it is possible that he refers to the message-key unit that was used on the T52C machine. The use of the terms `transposition relay' and `transposition circuit' does not refer to the machine's permutation of the Murray code elements, but rather to a basic circuit-building block, the transposition unit, which contained a double change-over contact. This basic building block was used to perform all the necessary operations of modulo-two addition and permutation of the teleprinter code elements. A total of fifteen transposition units was used to construct the message-key unit. The T52C machine was the only machine to employ this feature.
3.Due to an anomaly of the rotor movement in the Enigma machine, the 2nd or middle rotor will step twice every time the 3rd or left rotor is advances. Therefore the period is 26x25x26 = 16900 instead of 26x26x26 = 17576, but the machine has a total of 17576 starting positions.
4.There is some slight confusion here about the terminology. The early Siemens T52A/B machine (1937) was called Geheimzusatz while the Lorenz SZ40 and SZ42 machines were called Schlüsselzusatz (cipher attachment). The use of the Z designation for the SZ40 machine probably comes from the German use of the letter Z to describe this machine while setting up an encrypted communication circuit. To set up encrypted communication with the T52A/B they would transmit in clear the Q-code ``QEK'', while for communication with the T52C and the SZ40 machines they would transmit ``QEK C'' and ``QEK Z'' respectively.
5.The author uses the term ``transposition connection'', which is correct in the sense that it transposes the function of a given code wheel, but it is a term likely to be confused with the machine's permutation circuit or the transposition unit. The translator has therefore decided to call this part the selective or programmable connection.
6.Because the enciphered text can contain any of the 32 possible teleprinter combinations, including the six control signals, the teleprinters used for interception had to be modified. In these specially modified teleprinters the signals carriage return, line feed, letters, figures, space and null were replaced with the numbers 1,2,3,4,5 and 6. All the other combinations were represented by their corresponding letter as normal. The British codebreakers at Bletchley Park used a similar arrangement where they repaced the six control signals by the characters 4, 3, 8 or -, 5 or +, 9 or . and /. See Appendix A.
7.The construction of the decryption units, Apparna, was led by engineer Vigo Lindstein of L.M. Ericson's cash register department.
8.The breaking of the SZ40 machine was based on intercepted radio traffic, but some SZ40 traffic appeared also on the normal telegraph lines. This traffic covered the period from 26 November 1941 until March 1943 and the first Swedish break into the SZ40 took place on 9 April 1943.
9.The codebreakers at Bletchley Park made a break into the Siemens T52 machine during the summer of 1942. They had followed the use of this machine that BP called Sturgeon for some time. The T52 machine was mainly used on radio teleprinter links belonging to the German Air Force and the German Navy. Due to a question of priorities BP allocated their resources on the German Army links that used the Lorenz SZ40 and SZ42 machines. However, it appears that the Swedish codebreakers were the first to break the Siemens T52 machines.
10.It is more likely that the crypto department was looking for probable words or ``cribs'' than testing for correct decryption.
11.The author refers here to Commodore Torgil Thorén the chief of the Defence Staff's crypto department. The review of the Nyblad case is part of Thorén's analysis, which is included as Appendix 6 in the 1946 report ``Investigation into the Defence Staff's handling of decrypted messages from FRA''.
12.It is not entirely clear which machine the `Y-machine' refers to. It is possible it is the Siemens one-time-tape machine T-43 which towards the end of the war was used on radio communication circuits that also used the SZ40/42.
13.The Japanese machines, Purple, Coral and Jade, were used for high-level diplomatic communications and therefore never carried the same kind of tactically important traffic that was the case for the Enigma. Nevertheless, intelligence from these machines was important for the conduct of the war, and the reports from Japan's ambassador in Germany, Ōshima Hiroshi, contained much information of great strategic value.