Friday, June 29, 2012

German microwave communications of WWII

During WWII the Germans used microwave communications in areas where it was not possible to have landlines. This was either due to geography or for military reasons (partisan interference etc).

There were several types of microwave equipment. The main types were:

1.     Michael - DMG 4,5 (one speech plus 3 teletype channels)

2.     Rudolf -DMG 3aG  (9 channels)

3.     Stuttgart I and II - Fu G 03 (10 channels)

These types could be used together with carrier frequency equipment which allowed for several teletype links to be passed on each channel.

A good source on the German comm equipment is

The microwave equipment was used in all theaters. After the German forces in Stalingrad were surrounded it was this type of equipment that allowed for voice communications with the outside world.

The equipment used had a max range of 40km so in order to extend this to 110km it was necessary to find the highest possible location. The Germans built a tower on a hill near Nizhnyaya Chirskaya and during the night they raised the microwave tower and communicated with the encircled forces. During the day however they dismantled the tower because the Soviet airforce would destroy it.

This link was used by general Paulus to communicate with general von Manstein and other high level personnel.

Voice communications were not available after 22 December ’42 due to the withdrawal of the German front. [Source: FMS D-271The Battle of Stalingrad. Signal Communications in the Pocket of Stalingrad and Communications with the Outside’]

Other examples are available from FMS P-132Signal Communications in the East. By General der Nachrichtentruppen Albert Praun’, (available through






Monday, June 25, 2012


I added information from ‘Hitler’s Spies’ and 'Historical dictionary of German intelligence' in German intelligence on operation Overlord.

Specifically in these paragraphs:

1.     Luftwaffe reconnaissance

2.     Polish resistance movement code London-Warsaw

3.     Uncontrolled spies

4.     SIS-SOE codes

Sunday, June 24, 2012

Insecurity of Greek codes - Part 2

In a previous piece I looked into the lack of security of Greek codes during WWII. The systems used by the Greeks were solved cryptanalytically by the Germans.

It seems that post war both the Soviet Union and Britain were able to gain access to our secret diplomatic communications. This time however it was thanks to ‘bugs’ and spies rather than cryptanalysis.

One step forward, two steps back…

Let’s take a look at the relevant information:

From ‘The Mitrokhin Archive-The KGB in Europe and the West’, p458

Despite the Sixteenth Directorate's reluctance to share most SIGINT secrets with its intelligence allies, it depended on their assistance. With the growing complexity of computer-generated cipher systems, Soviet cryptanalysts were increasingly dependent on the penetration of foreign embassies to steal cipher materials and, when possible, bug cipher machines and teleprinters. During 1974 alone joint operations by the FCD Sixteenth Department and its Soviet Bloc allies succeeded is abstracting cipher material from at least seven embassies in Prague, five in Sofia, two in Budapest and two in Warsaw. Soviet Bloc intelligence services also shared some of their agents in Western embassies and foreign ministries with the KGB. Among those who were particularly highly rated by the KGB Sixteenth Directorate was a Bulgarian agent codenamed EPIR, a security official in the Greek foreign ministry recruited by Bulgarian intelligence in 1966. Over the next ten years he assisted in the removal of over 12,000 classified pages of documents from the ministry.

From ‘Spycatcher: the candid autobiography of a senior intelligence officer’, p113

After STOCKADE, plans were laid to attack most European ciphers, starting with the Germans. But after much effort, we aborted the operation, because their machines were too well screened. But we successfully placed a probe microphone behind the cipher machine in the Greek Embassy in London. This was a particularly valuable target, since the Greeks were giving considerable support to Colonel Grivas, the Cypriot guerrilla leader, during the Cyprus Emergency.

From 'SOVIET COMINT IN THE COLD WAR' by David Kahn in Cryptologia (Volume 22, Issue 1, January 1998, pages 1-24), p8-9

Kahn’s information comes from an interview with Victor Makarov a translator of Greek intercepts at the KGB’s 16th Directorate. Makarov gives several examples from the messages he translated:

During the Israeli siege of Beirut in August 1982 the Greek ambassador had a meeting with Yasser Arafat who asked for the Greek prime minister Andreas Papandreou to intervene diplomatically.

In 1981 a message from the Washington embassy had details of a meeting between the Greek ambassador and American officials which concerned events in Eastern Europe and especially the Solidarity movement in Poland. The Russians found the information very interesting.


Greek communications security was poor during WWII. It seems that post war this problem was corrected by using cipher teleprinters with OTP tape.

However during the Cold war interested parties were able to sidestep the unbreakable OTP code by using ‘bugs’ and spies.

Small countries should make every effort to protect their communications. Are Greek communications secure today? Probably not.

Friday, June 22, 2012

German intelligence on operation Overlord

In the summer of 1944 the German army suffered two horrific defeats that sealed the fate of the NS regime. In the West the Anglo-Americans were able to invade France and after hard fighting in Normandy they routed the German forces in the West and liberated France.

In the East a huge Soviet offensive against Army Group Centre in Belorussia resulted in a crushing defeat for the Germans and the liberation of the last part of occupied Soviet territory.
Operation Overlord was the Anglo-Americans plan to invade and liberate France. It had been planned thoroughly and huge military forces were assigned for it.

One of the most interesting questions of WWII history is whether the Germans could have taken measures that would lead to a defeat of the Allies in the West. Many authors and historians claim that the Germans had huge forces in the West but were prevented from moving them to Normandy because of a deception plan. I have criticized this belief here and here. The problem is that the positioning of German divisions in the West does not correspond with that theory.

Sunday, June 17, 2012

The Irish Government Telegraph Code

In the course of WWII the diplomatic communications of the neutral countries became a target for the codebreakers of the Allied and Axis powers. Although Ireland was a small country the Irish diplomatic codes attracted the attention of the German Foreign Ministry’s Pers Z and Goering’s Forschungsamt. These two organizations were able to read the Irish codes during WWII.

The Republic of Ireland used for its secret diplomatic communications the British Government Telegraph Code, a five-letter, one-part, 84,000 group system. This was used unenciphered for low level messages and enciphered for more important traffic. The Germans had managed to capture a copy of the Government Telegraph Code from the British consulate in Bergen, Norway in 1940.
The section of Pers Z that was responsible for Irish codes was Dr Ursula Hagen’s group. This covered England, Ireland, Spain, Portugal and Latin American countries. Technical Assistant (Wissenschaftliche Hilfsarbeiterin) Dr.  Ursula Hagen was born March 23, 1901. She entered Pers Z S on October 1, 1922 and by 1939 (and through 1945) she was head of the group which was responsible for work on England, Ireland, Spain, Portugal, and Latin American countries. In 1942 her group had 12 people assigned to it (1). 
Irish codes were also worked on by Goering’s Forchungsamt. The Forschungsamt’s Abteilung 7 had considerable success (‘ziemlich laufend’) with Irish codes up to the end of the war (2). Abt. 7 covered: USA, England, Ireland, South America, Spain, Portugal, Turkey, Egypt and Far East. Personnel were roughly 60-70.
More details on the Irish codes are given in TICOM I-172 Interrogations of Hagen and Paschke of Pers Z S’, p3-4

11. Eire
HAGEN described the work done by Pers Z S on Irish Diplomatic substitution recoding tables for use with G.T.C. There were 26 hatted alphabets, each group being taken from one alphabet. The alphabets were not necessarily used in order but always systematically. The last group of a telegram indicated the system to be used in the next message, e.g, if the last group was recyphered with alphabet 5, then this alphabet would also be used for the first group of the next message. The tables changed at irregular intervals - only about four times during the war. Different keys were used for various posts, e.g. Berne, Rome, Berlin, Paris, Madrid. The traffic became more difficult to read in 1942-43, when there was insufficient material and not enough staff. Then the Forschungsamt started work on it and solved the Berlin and Madrid links. Pers Z S took over the keys from the Forschungsamt in 1944. The first three figures of the message gave the page number, the fourth figure the number of the block, and the fifth and sixth figures the line-numbers. This new system used a 300-figure subtractor; each end of the link was allotted 25 such keys, e.g. 25 Dublin-Berlin and 25 Berlin-Dublin, etc. If the length of the message exceeded 300 figures, the key was repeated, but a new key was used for each new message, always in the order 1 to 25.
Messages consisted of reports from the Irish minister on the state of affairs in Germany. The Staatssekretär was interested in diplomatic reports on the trend of events, air-raids; etc. The traffic was regarded as valuable by Ribbentrop and some messages were shown to Hitler. HAGEN said that with any luck six fairly long messages were sufficient to break a new substitution recoding table, and this work took less than a week.
Irish messages in plain G.T.C. did not provide information of any value.

Translated Pers Z reports from 1941 and 1942 confirm these statements (3). The 1941 report says that ‘all the Irish telegrams can be read completely’ and 223 decoded telegrams were published. In 1942 126 decoded telegrams were published.

Some decrypted Irish telegrams from 1944 can be found in the TICOM collection of the German Foreign Ministry’s Political Archive (4), for example:


(2). TICOM report I-54 ‘Second interrogation of five members of the RLM/Forschungsamt’, p2-3

(3). British national archives HW 40/180 ‘PERS Z-S, the Diplomatic Decryption Bureau of the German Ministry of Foreign Affairs: reports and POW interrogations’ (Annual report of section dealing with British empire, Eire, Thailand, Portugal, Spain and Latin America).

(4). German Foreign Ministry’s Political Archive - TICOM collection – File Nr. 795 Irland 1944 Entschl. Verkehr (übersetzt) zw. d. versch. Irischen Botschaften

Thursday, June 14, 2012

The Soviet K-37 ‘Crystal’ cipher machine

The Soviet Union used during WWII a large number of 2,3,4 and 5-figure codes of various types. These were all hand systems. When it came to machine ciphers they had in 1941 three different machines in service, the K-37 ‘Crystal’ off-line machine and the M-100 and B-4 cipher teleprinters.

The K-37 was a copy of the Hagelin B-211 with Cyrillic characters on the keyboard. According to before the outbreak of WWII, Boris Hagelin was forced (by the Swedish authorities) to sell two B-211 units to the Russian Embassy. The Russians took the design and copied the machine. At the same time they converted the 5 x 5 matrix into a 5 x 6 one, in order to accommodate more characters. It allowed 30 letters of the Cyrillic alphabet to be used.

According to a very interesting article in production started at Leningrad plant No 209 in 1940 and by the summer of ’41 roughly 150 K-37 machines were in use.

The Germans were able to capture one K-37 machine in 1941 and they evaluated its security. They found that it had low security and could be solved on a 10-letter crib.
The war diary of Inspectorate 7/VI shows that in August ’41 a captured Soviet cipher machine was examined by the cryptanalysts Pietsch, Denffer and Hilburg and a report was prepared.

In September the analysis of the device was complete:

A detailed evaluation of the K-37 is available from TICOM report DF-217 ‘Russian cipher device K-37’, written by dr Grimmsen.

The device was ‘well built from the view of construction’ but the cryptographic security was ‘only conditionally sufficient’. According to a captured report from September 1941 it had not been put into use at that time but the goal was for it to replace all other cipher systems. 

From the TICOM reports it seems that the Germans never had the chance to try their theoretical solutions on actual traffic, as the machine was not used by the Soviet forces in the West.
This is confirmed by the war diary of Inspectorate 7/VI, since no further references to the K-37 can be found, apart from a study in October 1942 on intercepted messages that reached the conclusion that they were not enciphered on the K-37.

Information from TICOM reports:

From TICOM I-2 ‘Interrogation of Dr. Huettenhain and Dr. Fricke at Flenshurg,21 May 1945’, p1-2



From TICOM I-64 ‘Answers by Wm. Buggisch of OKH/Chi to Questions sent by TICOM’, p4

This was an electrical machine, almost exactly similar to the French B 211 but without the "Ueberschluesseler"(added E. wheel at one point) of the B211. It was considerably less secure than the B211 and a theoretical solution was worked out which did not need much text. B. had forgotten the details on this. The K37 had been captured, but never really used by the Russians.
From TICOM I-58 ‘Interrogation of Dr. Otto Buggisch of OKW/Chi’, p5

K-37 - A Russian machine, same principle as B211, but more primitive model was captured in 1941, and a theoretical solution worked out by HILBURG and Dr. V. DENFFER. They found it could be solved on a 10 letter crib. The work remained purely theoretical as no traffic in the machine was ever received.
From TICOM I-92 ‘Final Interrogation  of Wachtmeister Otto Buggisch (OKH/In 7/VI and OKW/Chi)’, p4

10. K-37 differed from B211 in lacking the "Surchiffreur", or ‘’Ueberschluesseler’’, a sort of Enigma wheel by which the path of the current was turned to another channel at one point, crossing  over and exchanging positions with another path instead of continuing parallel. Buggisch called this an X effect, and said it greatly complicated analysis, as it was hard to tell when it was being employed in place of the parallels.

Perhaps the K-37 was not used in the Western areas of the Soviet Union because its low security had been discovered by Soviet cryptologists or they learned that one of their machines had been captured and suspected that the Germans had found a solution.
However the German assertion that the Russians never used the K-37 is not correct. It was definitely used in the Soviet Far East in 1945. The Americans intercepted this traffic. It seems reasonable to assume that the K-37 was also used prior to ‘45 in the Soviet Far East.

Postwar history
The captured German K-37 was apparently handed over to the Western Allies at the end of WWII. The Americans built an analog model of the K-37 which they called Sauterne Mark I.

This machine was attacked after the war by the Anglo-American codebreakers. It was used on Red army circuits in the Far East.
In February 1946 US cryptanalysts managed to reconstruct its internal settings, in March the first message was decoded and by April a regular supply of decrypts was being produced.

The US success was short-lived as K-37 traffic dried up by 1947.
Sources:The Secret Sentry’,, various TICOM reports, Intelligence and National security article: ‘Behind Venona: American signals intelligence in the early cold war’, ‘The Russian Target’ by Matthew M. Aid, cryptomuseum

Tuesday, June 12, 2012


Time for some new TICOM reports:

I-90 ‘Interrogation of Herr Reinhard Wagner (OKW/Chi) on Japanese systems’ - 1945

I-109  ‘Translation of a Report by Lt. Ludwig of Chi Stelle OB.d.L, based on questions set for him at ADI(K)’ - 1945

I-119  ‘Further Interrogation of R.R. Voegele and Major Feichtner on GAF Sigint’ - 1945

I-154 ‘Interrogatlon of Uffz. Rudolph Schneider of In 7/VI’ - 1945

I-155  ‘Report by Ostuf SCHUEDDEKOPF on the Forschungsstelle Der Deutschen Reichspost at Langenveld near Eindhoven’ - 1945

I-186 'Interrogation of Oberpostrat Kurt VETTERLEIN on Attempted Tapping of Transatlantic Cables’ - 1946

I-202 ‘Interrogation of Min Rat Viktor Wendland of OKW/Chi’ - 1946

I-204 ‘Preliminary interrogation report of  former Regierungsbaurat  Johannes Anton Marquart of OKH/Gen.d.NA’ - 1947

Report of interrogation of Kurt Friedrichsohn - 1947
CSDIC/CMF/Y 40 - 'First Detailed Interrogation Report on Barthel Thomas’ - 1945

Available both from my Google Docs and Scribd accounts.

Also added professor Hoheisel in German mathematicians in the cryptologic service and made a change in  The US TELWA code regarding the SIGRIM code. This was the US War Department Telegraph code 1919 edition and not 1938 as i had written.

Sunday, June 10, 2012

The US TELWA code

In a previous piece on the M-209 cipher machine there was mention of the US TELWA code. Reinold Weber a member of NAAS 5 in France described the solution of this code in his interview by Klaus Schmeh.

The TELWA code was the US War Department Telegraph Code 1942 edition (SIGARM). The previous version was WDTC 1919 edition (SIGRIM). Both codebooks were used without additional encipherment, mainly for administrative traffic. Information on these cryptologic systems is available from the US National Archives and Records Administration - collection RG 457 - Entry 9032 - boxes 797 and 961. According to documents found in these boxes the WDTC 1919 edition was used till 1943/44 and the WDTC 1942 edition was introduced in 1943 but had a shorter life than its predecessor since it did not survive the war.


Thursday, June 7, 2012

The codebreakers of the Hungarian General Staff


Hungary, despite being a small landlocked country had an effective cryptologic service during WWII. The crypto service belonged to department X of the 2nd Division of the General Staff. It was located in the building of the Ministry of Defense in Budapest.

The department was headed during the 1920’s and mid 30’s by colonel Kabina. Then colonel Pokorny took over and finally colonel von Petrikovic.

Strength was about 35-50 people. Emphasis was given on the codes of Yugoslavia, Bulgaria, Turkey, Rumania and Italy. Their top cryptanalyst was Titus Vass and he was assigned to Turkish codes. Their successes were based not only on cryptanalysis but also on physical compromise.

According to German reports the Hungarians intercepted mostly diplomatic traffic from the Balkans and had good results on Turkish and Bulgarian codes. They cooperated with OKW/Chi from the 1920’s on Italian traffic but later extended this deal to cover other countries too. During WWII they also shared their work with the German security service SD. The Luftwaffe established an undercover monitoring station in Budapest in 1938 but cooperation with the Hungarians was poor.

The Hungarians also exchanged results with the Italians, the Japanese and the Finns.

At the end of the war the whole department was moved around. First to Steinamanger/Szombathely in Hungary and later into Germany .One report says they hid their archives ‘somewhere in Eastern Bavaria’. These would be the documents recovered by a TICOM team at Eggenfeld, Germany. According to EASI vol8 90 books were recovered at that location, indicating that the Hungarians had success with the codes of Belgium, Bulgaria, Denmark, France, Greece, Italy, Netherlands, Portugal, Rumania, Croatia, Sweden and the Vatican.

Relationship with foreign agencies:

Connection with OKW/Chi

The Hungarians had a long connection with the deciphering department of the Wehrmacht High Command.

In 1923 the Hungarians sent Colonel Kabina accompanied by colonel Pokorny to Berlin and they quickly reached an agreement with their German counterparts on the exchange of Italian material.

This cooperation was later extended to cover other countries and there was a constant courier between OKW/Chi and Budapest.

For the Germans the Hungarians were important because they provided them with radio intercepts, especially from the Balkan area. Fenner, director of cryptanalysis at OKW/Chi did not hold their codebreaking skills in high regard.

The Hungarians were also important due to their success in photographing the enciphering tables used with the US Military Intelligence Code No11. This code was used by US attaches around the world, including a mr Fellers in Cairo…

Connection with the Forschungsamt

OKW/Chi employee Victor Wendand mentions in TICOM I-202 that when he was returning from a visit to the Hungarian crypto service he met Seiffert, an employee of the FA who was visiting the Hungarian Abwehr (intelligence service). No other details are given.

Connection with the Sicherheitsdienst

The SD was the intelligence service of the SS. The Hungarian codebreaking department shared its results with the SD for a price.

This connection is described by SS Obersturmbahnfuhrer Urban, Liaison officer of RHSA/VI (foreign intelligence) with the codebreakers of the Hungarian General Staff.

According to Urban he was given decoded messages by the Hungarians and he translated them into German and sent them to SD headquarters. Work was heavy for Urban and his small group as they received 40-100 messages daily.

Wilhelm Höttl, head of SD foreign intelligence for Southeastern Europe, also mentions the decodes he got from the Hungarians in his book ‘The secret front: the story of Nazi political espionage’.

Connection with the Luftwaffe Chi Stelle

In 1938 the Luftwaffe signal intelligence service established a ‘Weather Station’ in Budapest. This station intercepted and decoded Yugoslav and Rumanian traffic. Cooperation with the Hungarians was not good as they were considered to be poor codebreakers.

Connection with the Italians

According to EASI vol8 ‘liaison with the Italians on cryptanalytic matters appears to have been very good. The Hungarians maintained liaison officers in Rome and made the results of their work available to the Italians’.

Connection with the Japanese

The Japanese military attaché in Budapest Lieutenant Colonel Shinta Sakurai certainly cooperated with the Hungarians, especially on solving Soviet codes. Unfortunately not many details are known.

Connection with the Finns

The Hungarians supplied the Finnish cryptologic service with intercepts. They also gave the Brazilian codes to the Finns. [Source: David Kahn in ’Finland's Codebreaking in World War II’ in ‘In the Name of Intelligence: Essays in Honor of Walter Pforzheimer’]

Organization of the cryptologic service

There were ten departments:

1.     Turkish

2.     English and American (England, USA, South America, Egypt)

3.     French (France, Switzerland, Greece, Belgium , Holland)

4.     Russian (Russia, Bulgaria, Yugoslavia, Slovakia)

5.     Rumanian

6.     Swedish (Sweden, Norway)

7.     Italian (Italy, Vatican)

8.     Spanish (Spain, Portugal)

9.     ?

10.  Japanese (Japan,China)

Urban and Fenner give some details on the people employed in the Hungarian service:

Chief: von Petrikovic

Deputy: Szabo

Turkish - Head: Klaar, Cryptanalyst: Titus Vaas, Translator: Sesevits

English and American - Andreanszky, Szabo

French - Bonami, Baron Zech

Colonel Harmony- Serbia, Bulgaria and Croatia,

Colonel Radda- Denmark, Czechoslovakia

General  Pawlas - Rumania

Lieutenant Colonel Szallay - France,

Lieutenant Colonel Brcic, Edler Herr von Stary Gory - special field not known

Majors Erdoes (brothers) - Italy

Colonel Pogany - Poland.

Lieutenant Colonel von Andreanszky, Poland (?)

Ministerial Government Councillor Dr. von Ujfalussy - England and America

Intercept service – Major Bibo

Sources: European Axis Signal Intelligence vol 8,  I-193 ‘Interrogation of SS Obersturmbahnfuhrer Urban, Liaison officer of RHSA/VI with the crypto bureau of Hungarian General Staff’, I-202 Interrogation of Min Rat of Viktor Wendland of OKW/Chi’, DF-187 ‘The career of Wilhelm Fenner with special regards to his activity in the field of cryptography and cryptanalysis’, DF-187D ‘Relations of OKW/Chi with foreign cryptologic bureaus’, The secret front: the story of Nazi political espionage, ‘Japanese Intelligence in World War II’ by Ken Kotani, ‘In the Name of Intelligence: Essays in Honor of Walter Pforzheimer’, Wikipedia (for the flag)

Tuesday, June 5, 2012

RAF Bomber Command strength 1939-45

The British Royal Air Force was organized in specialized commands. Bomber Command’s role was to engage in a strategic bombing campaign against the enemy’s population centers and industrial areas.

Let’s have a look at the Bomber Command strength from AIR 22 - 'Air Ministry: Periodical Returns, Intelligence Summaries and Bulletins':

Est.: Establishment strength in operational units.

Op.: Aircraft in operational units.

Serv.: Serviceable aircraft in operational units.

Crews.: Aircraft in operational units with crews.

Some comments:

For the first half of the war the StrategicTM RAF has no strategic (4-engine) bombers.

Bomber Command strength goes up in the period 1939-42 but then there is a slight decrease in numbers during ’42 as the new 4-engine bombers are introduced and the old tactical bombers are withdrawn from service. From ’43 numbers go up again. 

The rise in numbers is not rapid. This is due to two main factors:

1.     The inability of British industry to provide for a massive surge in 4-engine bomber production.

2.     The heavy losses inflicted on BC by the Luftwaffe’s Night-fighters (Nachtjagd) and the Flak forces.

Compared to the Luftwaffe’s Bomber force the RAF’s BC is numerically inferior in the period 1939-43.

Regarding the types of aircraft, it is interesting to note that many different types are used concurrently. For example in May ’41 there are: Blenheim, Wellington, Whitley, Hampden, Stirling, Manchester, Halifax.

Standardization wins out in the end. In May ’44 there are only four types in use: the Mosquito, the Lancaster, the Stirling and the Halifax.

The effects of Lend Lease are minimal when it comes to BC aircraft. Only a few Boston bombers are used in the period 1942-43 and the B-17 Fortress for a short time in 1941-42.

Further reading: An excellent study of the costs of BC for the British economy can be found here.

Friday, June 1, 2012

The American M-209 cipher machine

At the start of WWII the US armed forces used various means for enciphering their confidential traffic. At the lowest level were hand ciphers. Above that were the M-94 and M-138 strip ciphers and at the top level a small number of highly advanced SIGABA cipher machines.

The Americans used the strip ciphers extensively however these were not only vulnerable to cryptanalysis but also difficult to use.  Obviously a more modern and efficient means of enciphering was needed.
At that time Swedish inventor Boris Hagelin was trying to sell his cipher machines to foreign governments. He had already sold versions of his C-36, C-38 and B-211 cipher machines to European countries.

In 1940 he brought to the US a copy of his C-38 device. This was tested by American cryptologists and it was adopted by the US armed forces for their low/mid level traffic. Overall more than 140.000 M-209’s were built for the US forces.
The American version of the C-38 was called M-209 and had a few modifications compared to the original version. The M-209 had 27 bars on the drum while the C-38 had 29. Another difference was that the letter slide was fixed. During operation the text was printed automatically.