Seizing the Enigma (52 page)

The system was enormously complex. But it was formidably strong.

In addition, two kinds of messages were encoded for brevity before being enciphered in Enigma. U-boat sightings and other reports were condensed into four-letter groups by the Short Signal Book. Weather reports converted measurements into single letters using tables in the Short Weather Cipher. Thus, in Table 3 of the edition in use in 1941, atmospheric pressure of 971.1–973.0 millibars was represented by N, 973.1–975.0 by M. In Table 6, cirrus cloud cover of 1/10–5/10 became E. Using the Short Weather Cipher, the observer aboard ship converted his measurements into letters in a prescribed order. For example, a surface observation from 68° north latitude, 20° west longitude (northwest of Iceland) reporting atmospheric pressure of 972 millibars, temperature of minus 5° Celsius, wind from the northwest with force 6 on the Beaufort scale (a strong breeze of 25 to 31 miles per hour), 3/10 cirrus cloud cover, and visibility up to 5 nautical miles, would become MZNFPED. To this would be appended the two-letter signature of the reporting ship.

Part of a page of the Short Signal Cipher of 1941. This page deals with plans for attacking. Each four-letter group replaces a phrase. Thus
aabb
stands for “Intend to attack reported enemy forces in naval square …” The encoding shortens the message to be enciphered and provides an extra layer of secrecy.

Part of a page of the 1942 edition of the Short Weather Cipher, the edition captured from the U-559. In each table a letter replaces a meteorological observation. In Table 11, air temperature in whole degrees centigrade, 21° becomes
h
in the sequence of letters to be enciphered. Table 12 (not shown here) lists differences between air and water temperatures, and Table 12A (not shown here) the time of the weather observation.

A drawing from Arthur Scherbius’s U.S. initial patent for the Enigma. Figure 1 shows the typewriter keyboard (1), the input plate (4), the rotors (6, 7, 8, 9), and the output (12), here a perforator for a teletypewriter paper tape. There is no reversing rotor; the current goes through the rotor sequence only once.

A side elevation of an Enigma machine, from Willi Korn’s patent for adding notches to each rotor’s alphabet ring to vary the advancing of the adjacent rotors.

The route of the electrical current in the Enigma, as shown in a German navy manual.
Umkehrwalze
, reversing rotor;
Drehbare Schlüsselwalzen
, turnable rotors;
Eingangswalze
, entry rotor.

Part of the North Atlantic portion of the German navy’s grid of the world’s oceans. The chart is divided into approximate squares designated by pairs of letters, and each square is subdivided into smaller squares designated by pairs of numbers. The numbered squares could be further subdivided into smaller numbered squares for greater precision in location.

T
HE FOLLOWING ABBREVIATIONS ARE USED IN THE NOTES
:

Data on times of solution come from DEFE 3, which gives for each intercept the date and time of interception and the date and time of its dispatch to the Operational Intelligence Centre. The difference is called the solution time, which includes translation.

Figures for tonnage sunk come from Roskill,
War at Sea
, 1:615–16, 2:485–86, 3:388–89; Morison, 1:410–411, 10:365; and Rohwer,
Axis Submarine Successes
, All are in gross tons (sometimes called gross register tons), not deadweight tons or displacement tons.

Unless otherwise specified, all information in this chapter comes from ADM 1/11133; PG 30106; Roskill,
Secret Surrender;
and interviews with Baker-Cresswell, Balme, and Wilde.

PAGE

2
James Roosevelt:
New York Times
, May 10, 1941.

2
OB series: Rohwer,
Axis Submarine Successes
, 321.

4
Asdic: Hackmann.

4
radar errors: Kemp interview; RM 7/104:87; MacLachlan, 112; Rohwer, “La radiotélégraphie.”

6
less than 70 days: Hinsley, 1:163, 337.

6
two days before the attack: DEFE 3:1:2TP368.

6
126,000, 249,000: Roskill,
War at Sea
, 1:616.

6
rationing hurting, thinking with stomachs: Leonard Mosley,
Back to the Wall: The Heroic Story of the People of London During World War II
(New York: Random House, 1971), 225.

6
meat, cheese rations: Great Britain, Ministry of Food,
How Britain Was Fed in War Time
, 58.

6
31 million tons: Winston S. Churchill,
Secret Session Speeches
, ed. Charles Eade (New York: Simon and Schuster, 1946), 38, 49–50.

6
28 million tons: Schoenfeld, 126.

16
“Is there a chance”: Baker-Cresswell interview.

All details about the
Magdeburg
grounding, salvaging attempts, and code-book jettisoning are from Assessor Tolki’s report of Sept. 17, 1914, in PG 64859; Makela; Germany, Marine-Archiv,
Ostsee
, 1:76–85. Details of bringing the codebook to Britain are from Count Constantine Benckendorff,
Half a Life: The Reminiscences of a Russian Gentleman
(London: Richards, 1954); ADM 53/62801; FO 371/2095:490–509; Hammant.

17
Magdeburg
specifications: Gröner, 1:172, 175.

21
fourth lay hidden: The accounts in Tolki’s report in PG 64859 mention only three codebooks aboard the
Magdeburg—
those in the steering room and radio shack and on the bridge. All were said to have been burned or jettisoned. Makela, p. 49, lists the serial numbers of three codebooks: 145, 151, and 974. Both sources thus imply that only three books were aboard the cruiser. But the book sent to the British, 151, now in the Public Record Office as ADM 136/4156, shows no signs of immersion. It thus could not have been one of the three mentioned in PG 64859. The
Magdeburg
therefore had to have had four codebooks. Why is the fourth not mentioned in the sources? Because the crew members did not know about it, forgot it, or suppressed their knowledge of its existence in their testimony, while the serial number of one of the other three was not recorded or was lost. This seems to me more likely than the only other explanation that would account for No. 151 being captured dry: that it was left in the steering room, on the bridge, or in the radio room by Bender or Szillat or Neuhaus, who then, to avoid punishment, lied about throwing it overboard or burning it, while Galibin, to brag, lied about finding the codebook in the captain’s cabin, it really having been found elsewhere by him or another Russian. Makela’s statement,
p. 49, that the codebook on the bridge was not destroyed is contradicted by the statement on the next page that that codebook was jettisoned.