A pair of photographs taken in the district of Querum, in the north east of Braunschweig in Lower Saxony. Taken in 1941 according to the inscriptions verso, they depict Luftwaffe personnel in white denim 'Drillich' uniforms, typically used for work details, weapons cleaning and drill practise. This detail suggests that the photographs very likely depict communications training. The lid of the Enigma machine is propped up by a 4.5V Enigma machine battery, with one man operating the machine, two writing down the cipher-text, and another observing. An important point of note is that in all of the photographs, the machine's plugboard is not visible to the viewer. At the very least, with the sensitivity of this cipher equipment, the plugboard is obscured from the view of the camera.

A transcript document, headed “SECRET”, detailing decrypted German ciphered communications. It is thought to relate to the work of one of the USAAF’s Radio Squadron Mobile interception units, which dealt with intercepting and decrypting low-grade tactical messages. The document includes both the German plaintext and English translation. Some of the messages are quite ‘everyday’ sorts of messages, such as: “If there is no counter order, tonight the food and canteen goods will be given out taking into consideration the reserve (supplies). Klieninger” and “Impossible to receive you. Send more clearly”. There are also messages sent in the heat of battle, such as “Infantry in attack in company strength”, “AGJ 1 750 meters east of point 500 3 battle rate, (time fuse), S M (type of fuse) Infantry. Take up position and going into attack” and “To san uffz – One dead and one wounded left at hospital, Query – If Nitsche has arrived …”. There is mention in the document of the Flaksignalstafel, the German anti-aircraft signal code.

An illustration of an Enigma Handelsmaschine in an article titled ‘Die Chiffriermaschine: Ein neues hilfsmittel der Nachrichtenübermittlung’ (The cipher machine: A new tool for transmitting messages). The Handelsmaschine, described in the caption of the illustration simply as “Chiffriermaschine Enigma”, was developed in 1923 and was the first cipher machine sold under the 'Enigma' name. There are no known surviving examples of this machine and these illustrations are among the only images of it.

A photograph of an Enigma I machine operated by Luftwaffe personnel during the Western Campaign (Westfeldzug) in 1940. The location of where the photograph was taken is unknown, but it is likely either France, Belgium or the Netherlands. The Enigma machine is operated at a table, with an officer standing beside the Enigma operator and with a communications vehicle in the background. To the left of the Enigma machine is a field telephone with an operator writing down the message.

A keyboard from a German Enigma machine. The keyboard is in a damaged condition, missing some keys and the back row of springs. Some of the keys are functional, but some are not. It is possible that this keyboard was cannibalised for spares during the War. The keyboard was likely destroyed at the end of the Second World War in order to prevent it from falling in the hands of Allied forces. Fortunately left in an attic, the keyboard is in a remarkably good condition, and is one of the best surviving examples of an Enigma machine destroyed by German troops at the end of the War. Indeed, many ended up thrown away in holes dug in the ground or were thrown in the sea, so are now in a far worse condition. One of the keyboard 'legs' is the guide pin for an Enigma Umkehrwalze (reflector), evidence of a possible field repair.

An Enigma Umkehrwalze D (UKW-D, D Reflector), a rewirable reflector introduced for use by the radio networks of the German Air Force (Luftwaffe) as a means of improving communications security. This example, found among other D reflectors, was dug up from the ground - most likely from a pit filled with discarded German radio and cipher equipment when Germany surrendered in 1945. Therefore, it does exhibit some damage where a sharp implement appears to have been used to destroy it, and also some corrosion.

A cable for the plugboard (or steckerbrett) of a German Enigma I machine. This example is in a fine, though untested condition. The cable has certainly seen wartime use, and, given the context in which it was found, possibly post-war use as well. There is some fraying to one end of the cable.

A fragment of an Enigma Schreibmax, a small printer which attached to a naval M4 Enigma machine to print the encoded message. The Schreibmax replaced the need to take down the letters lighting up on the lamp board by hand. This example is in a fairly poor condition, but is nevertheless an extremely rare accessory. This fragment, which was discovered with the remains of an M4 Enigma machine, forms the left part of the base plate. On the top face of the fragment is a label that reads, "Bei gedrückter Taste des Schlüssels M Walzen nicht bewegen", although this is illegible due to corrosion.

A 4.5V battery produced by the firm Batteriefabrik Jäger KG, based in the town of Friedrichroda, in Central Germany. On the side of the battery is the approval mark, with the German Reichsadler. This particular battery was found installed in a German Zeiler portable lamp as it was not a type specific to the Enigma machine.

A box for an Enigma Uhr, sometimes referred to as the 'Stecker Uhr', or 'Plug Clock’, a device introduced by the German Airforce (Luftwaffe) in July 1944 to increase the cipher security of the Enigma machine. Manufactured by the Berlin firm Konski und Kruger, the Enigma Uhr replaced the patch cables on the Enigma machine's plugboard (Steckerbrett). Unlike the box housing the Enigma machine itself, the wood used for the construction of the box for the Enigma Uhr is of a much poorer quality - reflective of the state of German manufacturing late into the War. There is some damage to the box and the metal hinges have been replaced with strips of leather, likely evidence of a field repair. As explained by the label on the box "Bei drohender Feindgefahr Verdrahtung der Rasterscheibe zerstören!", meaning "When there is an imminent danger from the enemy, destroy the wiring of the grid disk!", the Enigma Uhr was also easily disabled before being overrun with the enemy. The quality of the Uhr's spring-loaded contacts and the way the cables were soldered onto the Uhr made it easy for the device to be destroyed quickly. Likely all that was needed was for the operator to pull the cables with one hand.

Four Kriegsmarine "Würfelschlüsselzettel" message forms accompanied in a book of grid paper with "Kriegsmarine" printed on the front cover. These message forms were purchased from the grandson of Wilhelm Gotthardt, a Kriegsmarine Minesweeper Commander. His service record is written on the document, which was likely used as spare paper in the early 1950s in his application to the post-war German Bundeswehr. He was involved in clearing mines until November 1947. He refers to the German Mine Sweeping Administration (GMSA) which moved its headquarters to Hamburg in December 1947, but was then quickly disbanded in January 1948.

A photograph of an Enigma I machine operated by Luftwaffe personnel. Both the location of the photograph, as well as the year. are unfortunately unknown. The Enigma machine is operated on a folding table of the type issued for communications use. The Enigma operator (of the rank of Gefreiter) is photographed keying letters into the machine, with a man on his left looking over him and a man on his right writing down the message (both of the rank of Flieger). The photograph has scalloped edges, typical of photographs of the period.

A photograph of three Enigma I machines operated by Wehrmacht personnel. Both the location of the photograph and the year it was taken are unfortunately unknown. The Enigma machines are shown in a space which appears to have been set up as a communications room. In the photograph there is an operator for each of the three machines and two other personnel to write down the messages, as can be seen clearly in the right of the frame. A print on this photograph appears in Tom Perera's book 'Inside Enigma: The Secrets of the Enigma and other Historic Cipher Machines'.

A British First World War instruction document titled "Instructions for the use of cipher in messages transmitted by O. W. Wireless conveying information from O.P.s". The notice, which was to be posted in every observation post (O.P), details what information needed to be transmitted in cipher and what could be sent in clear. It states that information as to the movement and positions of troops, names of units and formations needed to be sent in cipher.

A collection of photographs depicting Bombe operators from the Women's Royal Naval Service (WRNS). Included is a rare photograph inscribed as showing the Bombe outstation at Stanmore in 1943 as well as a seated group photograph of six Wrens which was also likely taken there. It is believed that 'Knight' identified below the latter photograph is Norah Boswell (née Knight) (1925-2018) who was a Bombe operator at Stanmore from 1943-45. Another of the photographs was taken at Somerton Manor in Somerset according to its inscription, which was occupied by the WRNS during the Second World War. The other photographs are at unidentified locations and there is also a portrait of the owner, Jane Peters. The photographs have been removed from an album at some stage, so some of the photographs mounted on board have unrelated photographs on the other side.

An Enigma Eintrittzwalze (or entry wheel) found among some spare Enigma I machine parts (see C0017 — C0019). As such, it is not installed in an Enigma machine, so does not have any wires soldered to the rear of its flat brass contacts.

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A cable for the plugboard (or steckerbrett) of a German Enigma I machine. Found among some other Enigma I machine parts (see C0016, C0017 and C0019) probably from the same machine.

A pair of sockets for the plugboard of an Enigma I machine, found among some spare Enigma I machine parts (see C0016 — C0018). One has a thicker diameter for the top plugboard pin and the other a thinner diameter for the bottom plugboard pin. Each plugboard was fitted with 54 of these sockets (two for each letter and one on each side for testing).

A group of personal and official papers relating to E.J.G. Hoare, an officer serving in the 302 Indian Special Wireless Section in India and elsewhere in the Far East, dating between 1945 and 1947. The Special Wireless Section was part of the so-called ‘Y Service’ signals intelligence collection organisation, which listened in to enemy radio transmissions. One document, a message from South East Asian Land Forces (SEALF) to Burma Command calls for Hoare to bring "certain TOPSEC and SECRET equipment and documents" to the headquarters of the SEALF in Singapore. This equipment and documents, another document elaborates, are CCBP OI22-6 and OI22-7 combined authentication systems, Slidex cipher devices and keys, as well as War Office Column sequence charts. The writing on the back of the message is an exercise in Boolean algebra.

A post-war wooden transport box for an Enigma I machine, probably made during the Cold War when Enigma machines were re-issued and original boxes were too far gone. This box, whilst visually similar to the wartime Enigma machine box, exhibits a number of subtle differences. The hinges and spare bulb holder are of a different style, the lock has a rounded pull tab, the spare plugboard cable holders are oak rather than bakelite, the metal alignment tabs are missing form the front flap, 'Klappe Schließen' is imprinted (not stamped) and the 'Zur Beachtung' instruction plate is a photocopy pasted to the inside of the lid.

A photograph of an Enigma I machine operated by Waffen-SS personnel. The photograph was taken in Russia, dating it to post-1941 (the German invasion of the Soviet Union). The collar tab of the soldier in the middle shows the distinctive 'SS' runes, making this photograph the only known photograph of the Enigma machine in use by SS personnel. The soldiers are seated on a fallen tree, with the Enigma operator balancing the Enigma machine on his lap. The operator appears to be changing the rotor settings of the machine and there are soldiers either side of him to assist in writing down enciphered or deciphered messages. The photograph has scalloped edges, typical of photographs of the period.

A very rare and unusual set of Enigma rotors (serial number K590D, rotors II, IV and VI). Discovered among communications equipment disposed of in Germany at the end of the War, it has a complex history. According to production records it was issued to the German Condor Legion during the Spanish Civil War. Afterwards, the machine were returned to Germany and rewired on 7 March 1944 for use by the Axis-aligned Croatian Home Guard (Kroatischen Landwehr — Hrvatsko Domobranstvo). Two of the rotors (V and VI) were produced separately to rotor II as extra rotors. Whilst records make no mention of the existence of rotor VI, these extra rotors were supposed to have been destroyed in 1944, but for unknown reasons were not. These are the only known surviving Enigma rotors issued to the Croatian Home Guard. The existence of spaces for nine turnover notches and the existence of rotor VI suggest that the rotors may have never reached Croatia, and may have been rewired yet again as Enigma KD rotors. However, this theory has not been confirmed.

A pair of German Baumuster T1 morse code keys. The keys have a bakelite socket, a lid with the notice 'vor den Öffnen Stecker herausziehen' (before opening pull plug out), with a high-voltage arrow and a circle above. They also have a cable outlet on the right side with a bend relief spiral. The keys are mounted on a black metal base with rubber feet to prevent slipping when on a desk.

A transit case for a KL-7 cipher machine. The case has a metal plate on the lid that reads: 'National Security Agency Carrying Case CE 80754'. The serial number that follows is illegible. In the lid, there are sections to stow a power cable, work light and a spare ink ribbon. There is red paint over the original green paint which may have been added to repurpose the case for a civilian use, possibly as a tool box.

A collection of three ciphered telex messages (on Mainenachrichtendienst and Deutsche Reichspost message forms), as well as documents and letters dated between 1937 and 1942. The ciphered messages were sent by a radio operator (with the surname 'Dabis') on the German battleship the SMS Schleswig-Holstein, and much of the other correspondence was sent from Germany, Venezuela, Cuba, England and Haiti. A four leaf clover has been preserved between the pages of one letter.

A photograph of two Enigma I machines operated by Luftwaffe personnel in a communications room. Both the location of the photograph and the year it was taken are unfortunately unknown. One Enigma operator (of the rank of Gefreiter) is keying in a message and another (of the rank of Flieger) is writing down the enciphered or deciphered text. Another Enigma operator (also of the rank of Flieger) is shown listening to a radio receiver via a headset. The photograph has scalloped edges, typical of photographs of the period.

A Second World War British Slidex cipher device marked 'Camp Staff Clancy'. The cipher device, a paper-based manual cipher system, includes two OPS/SIGS cards. It also has two sets of rulers — black (for divisional headquarters) and green (for battalion and other units). The Slidex is supposed to have three sets of rulers, the third being red (for army headquarters). The device folds in two, with the right side being the cipher device itself and the left half being a pocket for storage of spare cards, rulers and an operating instructions booklet. The booklet is not present in this example.

A German translation of William F. Friedman's 'The Index of Coincidence and its Applications in Cryptanalysis' made by Austrian codebreaker Andreas Figl in 1938. Titled: 'Die Anzeichen Der Zusammentreffen und Ihre Anwendung In Der Entraetselungskunt', it was based on a French translation of Friedman's text. According to correspondence between Figl and Friedman held by the United States National Security Agency (NSA), this translation was made by Figl upon the request of a 'friend'. Indeed, this can be seen in the handwritten inscription in this manuscript that states: "Meinem lieben Berufenen unseres geheimen Dienstes zur Förderung seiner Studien gewidmet. Wien, am 8. März 1938" (Dedicated to my dear recruit into our Secret Service, to expand his studies. Vienna, 8 March 1938). It is signed twice by Figl. A copy was later given to Friedman in the 1950s and is now in the Friedman Collection of the George C. Marshall Foundation, the only other copy of this text known to exist.

A manuscript containing notes on early cipher machine patents, with a focus in the latter section on the function of the Kryha and Enigma machines. Each record in the manuscript includes the Austrian patent number, date of registration, the inventor(s) and a description of its function. The earliest is a patent issued in 1909 to Serge Kanschine and Emil Jellinek-Mercédès for a cipher typewriter. Designed by Kanschine upon the request of Jellinek, who was a wealthy automobile entrepreneur, the cipher typewriter functioned via two series of disks, of which one series carries the normal type and the second series the cipher type. In the Enigma section of the manuscript, the function of Enigma machine A793, the first of 31 commercial Enigma machines purchased by the Austrian Government in the interwar period, is examined in detail. There are a number of previously unknown terms used in this section, including "Enigma Resultate" and "Enigma Kontra Maschine". This will require further research and translation. There are also a number of hand-drawn notes and fold-out diagrams showing Enigma rotor wiring.

A manuscript comprising of two parts. Part I: Begriffe (concept). Containing subsections: A. Bezeichnungen (description), B. Das eineindeutige Buchstaben-Quadrat-System (the unique letter-square system), C. Sonderformen des eineindeutigen Buchstaben-Quadrates (special forms of the unique letter square), and D. Bestimmung der Anzahl der verschiedenen Möglichkeiten der eineindeutigen Buchstaben-Quadrate, eineindeutigen Vokal-Quadrate und eineindeutigen Ziffern-Quadrate (determining the number of different possibilities of the unique letter squares, the unique vowel squares and the unique digit squares). Part II: Geheimschriften-Methoden, die sich auf das eineindeutige Buchstaben-Quadrat zurückführen lassen (Secret writing methods that can be traced back to the unique square of letters). Containing subsections: A. Das einzweideutige Buchstaben-Quadrat-System (the unambiguous letter-square system), B. Das einschtdeutige Buchstaben-Quadrat-System (the unique letter-square system), and C. Das einschtdeutige Buchstaben-Quadrat-System mit Monogrammen (the unique letter-square system with monograms).

A manuscript concerning the Bazeries and Schneider cipher systems, comprising of two parts. Part 1: Geheimschriften-Methoden System Bazeries (Cipher Methods System Bazeries). Part II: Geheimschriften-Methode System Schneider (Cipher Methods System Schneider). Both parts containing subsections: 1. Typisierung (typing) and 2. Verwandlung der Klarschrift in Geheimschrift (conversion of plain text into cipher text).

A manuscript comprising of two parts. Part I: Begriffe (concept). Containing subsections: A. Alphabet, B. Zyklen (cycles), C. Belegung (assignment), D. Zirkularscheibe (circular disk), E. Drehung (rotation), F. Pausen (breaks) and G. Allgemeinster Fall bei Arbeiten mit der Zirkularscheibe (most general case when working with the circular disk). Part II: Entraetselung (deciphering). Containing subsections: A. Die Geheimschrift (the cipher), B. Ermittlung der Periodizität (determination of the periodicity), C. Enträtselung im besonderen (deciphering in particular), and D. Rekonstruktion der zyklischen Komplexion des Klar-Alphabetes auf der Klarscheibe (reconstruction of the cyclic complexion of the clear alphabet on the clear disk).

A manuscript comprising of two parts. Part I. Einleitung (introduction). Containing subsections: 1. Allgemeines (general) and 2. Begriffe (concept). Part II. Teilungsregeln (division rules). Containing subsections: 1. Schlüsselvorschrift (key regulation), 2. Anzahl der verschiedenen möglichen eineindeutigen ziffernpaarigen Zuordnungen bei einem Normalalphabet von 26 Buchstaben (Number of different possible one-to-one digit-pair assignments in a normal alphabet of 26 letters) and 3. Teilungsregeln (division rules). The same subsections are repeated under 'Eineindeutige unregelmässige teils ziffernpaarige, teils ziffernupaarige Zuordnungen (Unregelmässigrer Zahlencaesar)' (One-to-one, irregular assignments, some of which have pairs of digits and some of which have only a few digits (irregular numbers Caesar).

A manuscript discussing offset systems (versatzsysteme). On the first page, the author states: 'Der Begriff des Versetzens kann folgendermassen festgesetzt werden: Die Klarbuchstaben der Klarschrift werden erhalten, die Klarstellen - das sind also diejenigen Stellen, die ein Klaruchstabe im Klaralphabet hat - werden nach einer estimmten Regel verwürfelt'. This roughly translates to: 'The concept of offsets can be defined as follows: the plain letters of the plain text are preserved, the clear places - these are the places that a plain language letter has in the plain alphabet - are scrambled according to a specific rule'. The author then proceeds to explore two types of offset (linear offset and areal offset), providing examples.

A manuscript containing codebreaking training exercises. Exercises include: 'Einsechsdeutige, periodische monogrammatische-monogrammatische Zuordnung' (Unique, periodic monogrammatic-monogrammatic mapping), 'Rekonstruktion des Klaralphabetes und des Geheimalphabetes bei einer Zirkularscheibe' (Reconstruction of the plain alphabet and the secret alphabet on a circular disc) and 'Lösung einer Transposition, vertauschung von zwei Ziffern' (Solution of a transposition, exchange of two digits). On an exercise dated 13th November 1936, the name 'Karl Jomansky' is written in the top-right corner.

A manuscript containing codebreaking training material, divided into 'Schulbeispiele' (schoolwork) and 'Hausaufgaben' (homework), as well as additional sheets with explanatory notes and diagrams. The content includes 'Chiffrierte Zeitangaben' (enciphered times), 'Eineindeutige monogrammatische-binumerale Zuordnungen mit Worttrennung' (unique monogrammatic-binumeral assignments with word separation) and 'Schlüssel regelmässige periodischer Systeme' (key of regular periodic systems).

A manuscript containing codebreaking training material, divided into 'Schulbeispiele' (schoolwork) and 'Aufgaben' (assignments), numbered 56-77. Many handwritten notes and annotations, as well as fold-out pages. Similar content to object C0037 'Schulbeispiele' (manuscript 1) and C0039 'Schulbeispiele' (manuscript 3).

A manuscript containing codebreaking training material, divided into 'Schulbeispiele' (schoolwork) and 'Aufgaben' (assignments), numbered 78-137. Similar content to object C0037 'Schulbeispiele' (manuscript 1) and C0038 'Schulbeispiele' (manuscript 2).

Three manuscripts bound together. The first is a manuscript concerning the deciphering of ancient inscriptions. Examples of inscriptions provided in the text include the Darius Naqsh-e Rostam inscription (a famous Achaemenid-era inscription located in Naqsh-e Rostam, Iran) and an inscription by the Persian King Xerxes. The second manuscript concerns encrypted telegrams and outlines and reproduces information from the various treaties and conferences in Europe regarding telegraphic communication. The third manuscript concerns 'non valeurs'.

A manuscript comprising of six parts. Part I. Begriffe (concept). Containing subsections: A. Definitionen (definitions), B. Einteilung der Codes (classification of codes), C. Anordnungen (arrangements), D. Einteilung der Codeworte (classification of code words) and E. Uebersicht über die Kapazität (capacity overview). Part II. Verschiedene Formen von Codes (various forms of codes). Part III. Code-Kennzeichen (code characteristics). Containing subsections: A. Codeworte-Anfänge (code word beginnings) and B. Codeworte-Enden (code word endings). Part IV. Morse-Verwandtschaften (morse relatives). Containing subsections: A. Zeichen (sign) and B. Zwischenräume (spaces). Part V. Condensers und ihre Kennzeichen (condensers and their characteristics). Part VI. Chiffriervorschriften (Transponiermethoden) und Entraetselungen (encryption rules (transposition methods) and deciphering). Containing subsections: A. Aenderungen am Codewort, hervorgerufen durch Aenderung an der Codezahl (changes to the code word caused by a change to the code number) and B. Aenderungen am Codewort, hervorgerufen durch Aenderungen am Codewort selbst (changes to the code word caused by changes to the code word itself).

A book issued with all naval Enigma machines to document repairs and modifications. This example has only one entry, dated the 7th of May 1945, a day before the German surrender to the Allied forces. M.N.O. is an abbreviation for 'Marine Nachrichten Offizier' (Naval Intelligence Officer). Molde is a port in the north of Norway. The serial number on this Begleitbuch indicates that it was issued to machine M10289. This puts it within the relatively rare range of machines with the manufacturer code 'gvx', which was used by Konski & Krüger's factory at Geyer, Saxony. According to Frode Weierud, 300 machines, probably between M10001 and M10300, were produced at Geyer. Fifteen of these machines, with serial numbers from M10119/gvx/44 to M10300/gvx/44, are known to have been used in Norway during the war. On the inner cover of the Begleitbuch is the warning: "Dies ist ein geheimer gegenstand. Missbrauch ist strafbar." (This is a secret item. Misuse is a punishable offense).

A book, titled 'The American', with an inscription addressed to Dorothy Gunn. The inscription, dated the 11th of December 1944, reads: "To: Dorothy Gunn An Englishwoman who understands and likes Americans, and who by her faith and genius has made a unique contribution to the success of American Air Power against Germany. Lewis F. Powell, Jr Lt. Col. A. C." Dorothy Gunn was an Air Ministry Civilian, TSAO(D) at Bletchley Park between 1941 and 1945. During her time there she worked in the Mansion, Hut 10 and Block A, (room 117) Block F(A), (room 21) Air Section - Air intelligence. Lewis F. Powell Jr. was a member of the Intelligence Staff of the United States Strategic Air Forces in Europe. Powell was assigned to Ultra, as one of the officers designated to monitor the use of intercepted Axis communications. He worked in England and in the Mediterranean Theater and ensured that the use of Ultra information was in compliance with the laws and rules of war, and that the use of such information did not reveal the source. He went on to become an Associate Justice of the US Supreme Court.

A crate with a paper inventory label on the inside of the lid describing its contents as "Chi. Maschine", likely an abbreviation of 'Chiffriermaschine' (cipher machine). The internal dimensions of the box match the dimensions of an Enigma machine (in a wooden transport case). On the label, there is a quantity column specifying that it is one of 50. According to the label, the crate was sent to field post number L31002, the 2nd Batterie Flak-Abteilung 506 (a heavy anti-aircraft battalion). On the label, there is also a round ink stamp with the German eagle in the middle that has another Dienststelle Feldpostnummer (with 'E' prefix that identifies a receiving/sorting unit) for that battalion.

A photograph of an Enigma I machine operated by Wehrmacht personnel in a tent. The stamp on the back: "Kopiert bei FotoHildenbrand Göppingen" (Copied at FotoHildenbrand Göppingen) suggests the photograph was taken in Göppingen, in southern Germany. Writing on the back reads: "Ein Funkspruch wird verschlüsselt" (A radio message being encrypted). The Enigma operator is photographed keying letters into the machine. The man on his left looking over him is possibly writing down the message. The photograph has scalloped edges, typical of photographs of the period.

An extremely rare Kriegsmarine codebook issued in 1940, containing bigram substitution tables for the Schlüssel H hand cipher used by German merchant ships (Handelsschiffe). The kennwort (code word) for this codebook is 'Hamburg'. Due to orders for this sensitive material to be destroyed after use, German codebooks from the Second World War, especially naval material, are extremely rare.