German success with high level codes of the Big Three

Thanks to the Ticom files and the recently released ''European Axis Signals Intelligence'' volumes it is possible to outline the success that the German codebreakers had against high level Allied codes.

In this post I will only briefly mention the codes.Each country will be dealt with in detail later on.

USA :

Top level military communications were covered by machine ciphers.These were secure.

However the State Department’s M-138 strip cipher (30 strips chosen from 50 ) was  compromised.Even the link carrying OSS communications from Berne was read by the Germans.Eventually however the State Department took measures to upgrade the M-138 security (strip elimination) and  the SIGTOT one time pad cipher machine was introduced.These two developments plugged the leak in late 1944.

The other system was the A-3 ciphony device used between UK-US in 1941-45.This was solved by two separate German teams ,one under the German Post Office  , the other under the German army.A fine example of German interdepartmental cooperation!

Honorable mention :

The Military Intelligence Code No11 ,used by the military attaché in Cairo Col. Fellers, did provide strategic information in 1941-2 ,so I’ll add this here even though it was not in itself a high level system.

Soviet Union : 

Army 5-figure code was read from 1940 to end 1944.

Army 4-figure  OKK – General Commander Code .Read from 1938/9 to 1942.( Discontinued after March ’42)

Cipher teletype used for communications between Moscow and the Fronts was solved by the Forschungsamt in 1943.(Possibly the M-100 ? )

Air Force 5-figure was first read in 1940 and probably solved throughout the war.

NKVD 4-figure emergency code. Used at times by almost all NKVD departments.Read during 1938-43.

NKVD 4-figure  . Used by NKVD interior troops, border guard and security troops facing hostile countries.Read  during 1942-45.

NKVD 4-figure  .Used by forward units of NKVD border guard and security troops.Used during 1943-45.Broken and read.

NKVD 5-figure used for railway transportation.Used during 1943-45.Broken and read.

Northern Fleet high level codes were read in 1942-43.Possibly 4-figure.

X ciphony device (German name for the Soviet equipment) was broken ‘’at will’’ at the Army Ordnance, Development and Testing Group, Signal Branch.It was in use from 1941-44.

Honorable mention :

The internal teletype and radio facsimile network intercepted by the Germans throughout the war provided economic and military mobilization data. However reading this traffic was a matter of building the necessary intercept equipment and not code breaking in the strict sense.

Britain :

War Office Cypher : Army universal high-grade codebook, carried traffic between Whitehall, commands, armies, corps and, later, divisions .Read In Middle East from  summer 1941 to January 1942.Home forces version read in early 1943 (traffic of 1942-Jan '43).

RAF Cypher  : RAF high-grade codebook. Broken  in March 1940,traffic read :Air Ministry and Gibraltar ,Malta ,Habbaniya ,Ismailia. From early 1941 until November 1942 traffic read in Mediterranean area.According to Voegele chief cryptanalyst of the GAF from Sept ’41 to Nov ’42 the majority could be deciphered within 5-10 days.

Inter-departmental Cypher : Used by Foreign Office,Colonial,Dominions and India offices and the services. Also used by Admiralty for Naval Attaches,Consular Officers,Reporting Officers. From Spring '40 to Spring '43 Middle East traffic (military and diplomatic) compromised. Weekly intelligence summaries sent by Admiralty to Naval attaches read extensively.

Naval Cypher No1 : First read in summer 1938.By April '40 ,30-50% read without delay.

Naval Cypher No2 : First read Sept '40.Oct' 40 setback (change in enciphering procedure) .Success from March '41  until Sept '41 limited ~10% ,from then on high.

Naval Cypher No3 (convoy cipher) : From Dec '41 read.Feb '42 reconstructed - up to 15 Dec '42  ~80% read.Then setback (indicator change).From Feb '43 success (10-20 hours in advance). From Feb '42 to June'43 regular decrypts of RN's U-boat dispositions.

Naval Cypher No4 : First read March '42.By Oct '42 reconstructed.Messages relating to convoy movements in the Pacific ,Indian ocean and Red sea were read.

Honorable mention :

Although according to the information available they did not have any success with the Typex cipher machine report Ticom D-83 says : ’However , by about May ,1941, OKH were in full possession of all the theory necessary for solving the problem and there can be little doubt that ,had they been lucky enough to capture a set of drums at Dunkirk as well as the three machines the bulk of the Typex traffic up to July 1940 would have been read’’.

This small presentation is a first step in straightening the record regarding  the battle between Axis and Allied codebreakers.

Sources: European Axis Signals Intelligence ,various Ticom reports , British intelligence in the Second World War vol2 , Intelligence and strategy: selected essays ,  report ADM 1/27186 . Russian cryptology during World War II, HW 40/7