signals intelligence warfare

1. Introduction

There is a good deal of terminological confusion about the broad field of signals intelligence (sigint) since it was not until 1943 that efforts were made to standardize terms commonly in use in the UK and USA. Sigint was held to consist of four distinct processes: (1)the interception of all signals, known as the Y-service in the UK and the Radio Intelligence Service (RI) in the USA;(2)the monitoring of traffic patterns and networks, designated as Traffic Analysis (TA);(3)the decryption or cryptanalysis of encoded or enciphered signals (see codes and ciphers);(4)the interpretation (including translation) of decrypted signals. These processes were located in the UK in the government Code and Cypher School (GCCS), set up after the First World War under Foreign Office supervision, but drawing personnel from the armed services (see Bletchley Park). In the USA, they were organized by separate groups within the Navy's Operations Division and the Army General Staff (see USA, 6).

Even greater organizational diversity prevailed in Germany, where the leading role was taken by the army; former army personnel ran the foreign ministry's small cipher section, while the navy organization was even smaller. In 1928, military Sigint was centralized within the Secret Service, the Abwehr, but in practice each service kept trained personnel within separate signals services, though in 1938 co-ordination of the three services was established under a Wehrmacht High Command (OKW). Initially, the first two processes were known under the term Beobachtungs-Dienst (or B-Dienst) within the navy—Horchdienst in the army and air force—and the third process was called the Entzifferungs-Dienst (E-Dienst). In 1933 a new Nazi Party-dominated service, the Forschungsamt, was established and eventually became the largest German sigint agency (see also Germany, 7). But no single central agency emerged, such as GCCS in the UK or the 8th Chief Directorate of the NKVD in the USSR, as each German agency expanded and tended to compete more strongly with the others. Each retained the terminology but, in practice, the secrecy within which they operated meant that each organization tended to cover all of these processes according to the resources and areas of concentration allocated to them. Italy and Germany began to collaborate from 1933 and Italian sigint organizations developed along parallel lines thereafter. The Japanese Army was influenced by Polish advisers in the early 1920s, while the Japanese Navy had had signals instruction from the UK since the late 19th century; army and navy developed rival sigint establishments, while the foreign and home ministries organized the principal civilian agencies.

Differences emerged in the forms of centralization or co-ordination according to bureaucratic or political demands in each country, but in every country there was a tendency for party political control to prevail and a tendency for each agency to engage in frequent organizational changes to maintain secrecy. Where the internal security of the state or ruling groups might be threatened by the effects of war, the interception of cable, telephone, and voice signals tended to be primarily delegated to the internal security services of the combatant powers, such as MI5, the FBI (see USA, 6), the NKVD or the Sicherheitsdienst (see RSHA) or divided between civilian (Tokkō) and military (Kempei) police in Japan. The onset of war, however, ensured that military agencies would gain resources and influence as a result of operational requirements. All these organizations, together with others concerned with what is nowadays known as electronic warfare intelligence (elint), photographic reconnaissance, the Radio Security Service (see MI6), the monitoring of the media and mail censorship, are now seen as integral parts of a country's communications intelligence (comint), the products of which are channelled to higher policy-making and operational bodies.

Sigint in practice related primarily to radio (or wireless) traffic since radio communications became the most important method of communication for the mobile aerial and land warfare that developed during the Second World War. During the inter-war period, all belligerent states invested heavily in the creation of extensive communications networks and in the monitoring of the preparations of other states, which had a direct impact on the conduct of operations in the early stages of the Second World War (see blitzkrieg, for example). Revelations about decryption successes in the First World War and in the early 1920s, directly connected with the revolution in Russia, led to investment in more advanced code and cipher systems aimed at protecting state communications. Soviet cryptographic advances after 1926 in particular stimulated the development of one-time pad systems for codes (where letter symbols were prevalent) and of electro-mechanical and, later, electronic machine ciphers (where number symbols were prevalent). These advances contributed not only to security in communications, but also to the apprehensions of neighbouring states, such as Poland, Germany, Hungary, Sweden, and Japan, and rapidly spread to the rest of the international system in the 1930s. The crucial balance to be struck was between minimizing losses in one's own communications security and maximizing penetration of the security of one's opponents' communications.

2. Joint and combined sigint

More than ever before, the effectiveness of sigint depended on the joint efforts of all agencies at every national level and the combined efforts of the belligerent coalitions. The success of any side depended to a considerable extent on a superior advance knowledge of an opponent's intentions and movements, particularly when the operational capabilities of each side were relatively evenly matched. Close German sigint collaboration with Italy, Hungary, Finland, and the Baltic States in the 1930s proved more effective in penetrating Anglo-French systems in 1939–40, and in assisting German operational successes during the Norwegian campaign and the fall of France in June 1940, than the individual progress made separately by Poland, France, and the UK up to the outbreak of war. British penetration of Italian systems in August 1940 was of direct value in improving communications security and in laying the ground for successful operations in the battles for the Mediterranean and the Atlantic in 1940–1. In 1941–2, however, Anglo-American advances with Japanese and German systems were still insufficient, combined with inadequate military preparations in the Pacific, to outweigh their losses of signals security.

Japanese intervention possibly lengthened the Second World War by 12–18 months, as the USA and UK failed to achieve an adequate level of signals intelligence co-operation with the USSR against Japan and were unable to commit Stalin to the war against Japan before the spring of 1945. The serious underestimation of Japanese operational capabilities was matched by an overestimation of the value of the pre-war penetration of Japanese diplomatic and naval signals security. Direct Anglo-American knowledge of the plans of the Japanese Army was not obtained until April 1943, though knowledge of Japanese naval operations played a crucial part in the decisive battle of Midway in June 1942 (see ULTRA, 2). Anglo-American ignorance about Japanese preparations for war in 1941 was compounded by an inability to penetrate Soviet signals security sufficiently to recognize the Soviet–Japanese commitment to mutual neutrality, without which Japan almost certainly could not have gone to war. Japanese sigint's most successful contribution (with some Italian and German assistance) lay in the independent confirmation, from a reading of state department radio cables, of the lack of American–Soviet accord on Far Eastern policy.

Severe German underestimation of the capacity of the Soviet system to resist, coupled with an overestimate of Japan's capacity to contain the USA and with an over-readiness to take on the USA at a time when Hitler already had cause to recognize an over-extension of German resources, was compounded by a steadily worsening balance of advantage in sigint warfare. Not only were German sigint organizations unable to make more than tactical inroads into Soviet communications security, and virtually shut out of US operational traffic from 1 January 1942 (and of British from June 1943), but also Anglo-American inroads into German and Axis cipher security became so extensive that the balance swung dramatically in favour of the Allied coalition for the rest of the war.

3. Surprise and deception

Many important cryptosystems in use by all belligerents were never resolved, usually because, even if they were intercepted, there were too few signals for them to be decrypted successfully, as decryption experts needed sufficient quantities of material to break a cipher. In many instances, greater security could be attained by minimizing or eliminating radio communications and resorting to cable, telephone, and landline, or courier services. Strict radio silence increased the surprise impact of offensive operations, and jamming, changes of wavelength, changes of code or cipher table, or changes of system, could have a temporary or more permanent effect on operational sigint agencies. On the other hand, elaborate efforts were made to deceive hostile sigint agencies, usually prior to major strategic moves such as BARBAROSSA or OVERLORD by organizing large amounts of dummy radio signals planned to simulate an impending offensive in a different direction from that actually intended, or in the case of the Japanese attack on Pearl Harbor, to disguise the true location of a striking force. Given the likelihood that success in reading operational signals was bound to be subject to gaps or delays in resolution, the techniques of direction-finding and traffic analysis were often the mainstays available to interpreters of offensive moves. Even when denied any possibility of successful decryption for most of the Pacific war, Japanese listening-posts were usually alerted to impending US offensives by increases in radio traffic across the Pacific. This ensured that general preparations could be made to make capture of Japanese-held territory a more costly business, especially in the end phase of the war.

4. Physical and covert retrieval

Military operations offered more opportunities for the physical seizure of communications equipment and code materials, but, except in cases where it was difficult to replace compromised systems quickly, or there were delays in confirming compromise, as in the case of the British cabinet papers taken from the liner Automedon off Singapore in November 1940, such seizures were of smaller value than covert photography of codes and ciphers. All states engaged in this kind of activity, but it was a favourite method of some states: for example, it was successfully employed by the Italian secret services (see Italy, 6) against the French, British, and Americans, and extended to their own allies, particularly the Japanese and the Romanians. The use of telephone taps (see also Forschungsstelle and Source K) and listening devices was also a valuable supplementary method of Sigint, as these were not only voice-activated, but could also record sounds of machinery such as typewriters and cipher machines, which could then be transformed into text form.

5. Signal security and alerts

Sigint security at national level was sometimes the responsibility of each agency and sometimes this was delegated to a single body, such as the NKVD's 8th Chief Directorate in the USSR or Bletchley Park in the UK, which were responsible for both diplomatic and military ciphers, or the Amtsgruppe WNV in Germany which supervised armed forces cipher security, but also tested the security of civilian systems unofficially. Generally, the military tended to be unconvinced of the security of their own diplomatic and civilian systems (as in the USA, Germany, and Japan) and tended to instruct military personnel to minimize reliance on such systems for the transmission of operational information. But bureaucratic rivalries also could lead to silence about insecure communications because that could confer some advantage domestically for one agency over a rival.

Nor were allies in the same coalition as frank as they might be about weaknesses in their systems. The UK, for example, hesitated to draw Soviet attention to some enemy tactical systems known to be penetrated in order not to compromise knowledge of British resolution of the ENIGMA machine cipher. Equally, the German Navy passed on decrypts of Allied traffic to Japan after 9 December 1941 only in its own cipher because of suspicions about Anglo-American inroads into Japanese systems. A German warning about the insecurity of Japanese diplomatic traffic (see MAGIC) in March 1941, and an Italian warning about the compromise of the traffic of the Japanese military attaché in Lisbon in 1943, led only to checks on the physical security of the relevant diplomatic premises, but not to any serious questioning of compromise through decryption. The Italians had an extensive monitoring network in the Western Atlantic, Indian, and Pacific oceans as well as the Mediterranean area. This considerably assisted German auxiliary cruiser operations from 1939 to 1941 and gave support to the Japanese Navy from 1941 onwards, but the Italians frequently had their warnings of compromised traffic ignored or rejected by their allies (see also Axis strategy and co-operation).

German suspicions of Italian losses of cipher security to the UK in the autumn of 1940 led to the dispatch of an advisory mission to Rome. But advice that every effort be made to keep German and Italian systems completely separate was ignored and ENIGMA equipment, previously loaned during the Spanish Civil War but upgraded in 1940, was allowed to be deployed selectively in Italian communications (see Cape Matapan). Fear that this would lead to a compromise of German systems was also ignored; even when leakages in German operational communications occurred in the Mediterranean theatre, it was always attributed to poor Italian security rather than to resolutions of ENIGMA systems. A more concerted effort was made in July 1942 to tighten joint security and this was extended to the Pacific at the same time as a result of the capture of papers from the Combined Operations Intelligence Centre in New Zealand on board the Australian steamer Nankin by a German auxiliary cruiser. These seemed to indicate a degree of compromise of Japanese naval systems that was reinforced by the subsequent loss of a Japanese naval codebook on Guadalcanal. The net result was an extensive tightening of security which increased Allied difficulties in reading Axis military systems in the second half of 1942. On the Allied side, by contrast, close Anglo-American co-operation in organizing a standard system for secure distribution of ULTRA intelligence by means of Special Liaison Units to theatre commands minimized leakages and this was steadily reinforced by a tightening up of British naval systems between the winter of 1941 and the summer of 1943.

6. The strategic value of diplomatic intercepts

The penetration of merchant shipping and diplomatic systems, including those used by military attachés abroad, or of individual members of the opposing coalitions, provided valuable clues about the strategies and operational intentions of the other members of the coalitions. Anglo-Polish collaboration in helping to make the earliest inroads into ENIGMA systems is well-documented. But it is much less well-known that German reading of Polish diplomatic and attaché traffic with Scandinavia provided insights in 1941 into the system most commonly employed by British military attachés for communication with both London and command posts overseas, the Interdepartmental Cypher. Such breaks, combined with information from the Naval Cypher and Naval Code and from Yugoslav and Greek traffic, were of great value for the German Balkan campaign and on Crete, as well as in highlighting British activities in the neutral countries of Europe, the Near and Far East and the Americas up to the introduction of one-time pads at the end of 1941. Italian and German successes with the US Black code up to September 1942 provided a flow of decrypts of detailed reports about British dispositions and plans for the Western Desert campaigns that were of great value for Rommel's defensive and offensive successes during 1942. German penetration of Merchant Navy Code and Naval Cypher No. 3 compromised Allied convoy movements in the battle of the Atlantic until July 1943 and offset the advantage the Allies had of virtually complete security of US naval systems after the USA entered the war.

Similarly, the US Army's resolution of the main Japanese diplomatic system in 1940 provided access to Hitler's briefings of the Japanese ambassador in Berlin, General Ōshima, about German offensive plans between 1941 and 1943 and to Ōshima's detailed reports about the state of German defences along the Channel coast. These advantages were enhanced by US resolution of the Japanese military attaché cipher in 1943 and UK resolution of Japanese naval attaché systems in 1944, covering developments in the whole of neutral and occupied Europe to the end of the war. Although it appears that little progress was made in persuading Soviet sigint agencies to exchange Japanese code materials, it was possible for the UK and USA to utilize the resolutions of Japanese systems, as well as German foreign ministry and Abwehr traffic, to promote frictions between Japan and Germany of the kind that had already been successfully promoted between Italy and Germany. For example, Allied disinformation about Japanese collusion with the USSR to permit a massive transfer of Soviet forces from the Far East to Europe convinced the German foreign minister Ribbentrop, who confronted and angered senior Japanese Army representatives in Berlin with accusations of disloyalty to the alliance in May and October 1943. Knowledge derived from decrypts was useful in generating frictions, but was much less effective in destroying the credibility of Japan as an ally in Hitler's eyes than had previously been achieved in the case of Italy, mainly by feeding enemy agents and diplomats in neutral countries with misleading, but plausible, information.

Allied penetration of Japanese communications shed much light on the wartime efforts to employ the USSR as a potential mediator in the Pacific war and Japan as a mediator in the German–Soviet war. But, after the war, even following the seizure of Axis archives and interrogation of participants in wartime decisions, the USSR remained, in Churchill's phrase, an ‘enigma wrapped up in a mystery’. Post-war defections and Soviet revelations about wartime intelligence activity in such cases as the RAMSAY ring in Japan (see Sorge) and the Rote Kapelle in western Europe have lifted only part of the veil from Soviet sigint. The USSR was probably the most successful state in protecting strategic communications from hostile sigint and in cloaking its intentions in 1939 and 1941 in order to avoid being drawn prematurely into the European and Pacific conflicts. But at the same time, its unwillingness to co-operate with the western powers deprived it of access to knowledge that could have significantly reduced the massive manpower and material losses accompanying its entry and involvement in the Second World War. The end of the Cold War has opened up Soviet archives, which may begin to answer many hitherto unresolved questions about Soviet sigint.

7. The role of the neutral states

The territory of the neutral states provided fertile ground for the sigint activities of the warring coalitions, as well as access to economic resources and technology. States such as Italy, Japan, and Spain early in the war were benevolently neutral towards Germany, which derived useful information-gathering opportunities from a presence on their territory, much as the UK benefited from US and Swedish benevolence. Both sides sought to derive advantage from their ability to read Turkish codes and ciphers as a means of deceiving and misleading their opponents.

Spanish territory was a significant battleground in covert warfare. Permission was given to the Axis states, in spite of constant Allied complaints to the Spanish authorities, to set up radio monitoring facilities on the mainland and the Atlantic islands, along with ship-reporting and supply facilities which directly supported U-boat operations in the Central and South Atlantic. Spanish government agencies provided a good deal of information otherwise inaccessible to each of the principal Axis states which was passed on to their representatives in Madrid throughout the war. On the other hand, the USA and UK derived benefit from their control of Spain's cable and telephone utilities and Allied agencies exploited their presence on Spanish (or Portuguese) soil to obtain Axis code materials and to disseminate misleading information, derived from decrypt evidence and aimed at the creation of frictions between Germany and its allies.

Although Switzerland and Sweden were particularly vulnerable to German threats, they sought to preserve as much independence as possible by an even-handed approach to the belligerent coalitions. Covert links were maintained with both Axis and Allied intelligence services. In the Swiss case, an exchange of intelligence was conducted by Colonel Roger Masson that traded information with both sides. In August 1943, for example, Masson informed the Abwehr that a contact in the US navy department had revealed that the real reason for Allied success in the battle of the Atlantic was the existence of a British Admiralty team responsible for breaking the U-boat cipher (see ULTRA, 1). The German Navy's refusal to accept the validity of this warning helped shorten the war. But it also indicates that, if a positive response had resulted, then the role of the neutrals could have had a more significant impact on both signals intelligence warfare and the length of the war.

The Swedish contribution to sigint was also of some significance. In the 1930s, the Swedish inventor Boris Hagelin (see also SIGABA) had tried unsuccessfully to sell his cipher machines to the German armed forces, but was more successful in parallel dealings with Italy, France, and the USA. In 1942, taps on German teletype lines to Norway passing through Swedish territory facilitated Swedish decryption of part of German military communications at a time when Sweden was particularly worried about a possible German invasion or becoming embroiled in the German–Soviet war. Information was supplied to the British naval attaché in Stockholm about German compromise of the Interdepartmental Cypher in 1941 and other information of value to the UK, such as further early warning of the departure of the battleship Bismarck.

On the other hand Swedish counter-intelligence authorities passed on information about Anglo-Polish and Polish–Japanese collaboration on Swedish territory both to the Abwehr and the Sicherheitsdienst, which supplied them with listening devices which were planted in the offices and homes of Allied diplomats. The Swedish foreign ministry allowed Polish military intelligence access to its courier service to send funds to, and exchange information with, the Home Army in occupied Poland until the discovery and arrest of numerous Swedish agents by the Gestapo in September 1942. These activities were linked to increasing evidence of the growth of a Soviet threat, already manifested in 1942 through Soviet submarine activity in Swedish territorial waters and in the sinking of Swedish shipping. Swedish intelligence agencies extended collaboration in intelligence-gathering against the USSR from 1943 to 1945 with the representatives of all the Axis states, including Finland, Hungary, and Japan, and aided them by putting them in contact with exiles from the former Baltic States, just as they facilitated Allied access to Norwegian exiles and contacts. From 1941 to 1943, the Japanese Army employed Polish contacts in Stockholm to supply information about developments in both the USSR and the UK and employed former Polish officers in Manchukuo to monitor and decrypt Soviet communications in the Far East, even though Poland and Japan were officially at war. After Finland was forced to seek an armistice in 1944, permission was granted to the Japanese military attaché in Stockholm to move the decrypt section of the Finnish Army General Staff to Sweden to continue its sigint operations against the USSR. In mid- 1945, the Japanese were also involved in attempts to infiltrate Estonian agents into the USA, but the Salzburg section of the Counter Intelligence Corps attached to Seventh US Army had already been forewarned of such a move by interrogation of a former Hungarian attaché in Sweden following the German surrender. Similar Japanese recruitment of Italian and German sigint and intelligence personnel occurred in China following the Italian surrender in September 1943 and the German surrender in May 1945.

8. Theatre and tactical sigint

Even the secure delivery of strategically significant sigint by central agencies to theatre commands was no guarantee that field commanders would invariably be able to exploit it effectively. The Poles and French, for example, were unable even to continue the war despite the successes they enjoyed in the reading of some of the early ENIGMA systems. An important lesson of the campaigns in the Western Desert, too, was the need for effective inter-service co-operation and for effective corps and divisional sigint organizations which provided intelligence for the higher command, as well as for a regular supply of high-grade ULTRA decrypts which often gave a decisive advantage to those actually fighting the battles. The performance of the Afrika Korps under Rommel showed what a well-integrated field intelligence system at the disposal of a small, but well-armed and skilfully led force could achieve against superior numbers. The application of systems analysis and operational research by the Allies to determine intelligence priorities and link them to organizational, logistical, and technical problems was an essential prerequisite for decisive military victory in offence as well as defence.

9. Conclusion

The importance of being able to intercept, decrypt, and analyse signals communications is that it is a highly economical method of building up a more comprehensive picture of a complex, global framework of economic, political, technological, and military interactions than could ever be gathered by huge numbers of spies. The authoritarian states, including the USSR, devoted a larger percentage of sigint manpower to domestic security roles than the Anglo-American states. The latter, therefore, achieved a more effective concentration of resources on the Axis coalition and a more rational division of labour based on a more effective sharing of knowledge and a higher standard of communications security, especially after December 1941. But because of their ignorance of Soviet communications and Japanese military systems, serious misjudgements were made by the western Allies about Japan's relations with the USSR and Germany, and about its operational intentions in 1941. However, the ill-effects of these were offset by a combined pooling of knowledge and allocation of resources in 1942 that stabilized the global balance of power. Drawing on previous experience of successful strategic defence and on vastly superior manpower, material, and technological resources, the western powers expanded sigint capabilities at every level and shaped them to serve offensive needs, while minimizing casualties. The Axis powers contributed to their own defeat by fighting separate wars and by sticking doggedly to the belief that their communications systems were impregnable. But it was also a remarkable tribute to Anglo-American communications security that that belief was not only reinforced at the time but, in the case of ULTRA, was sustained for three decades after 1945.

John Chapman

Bibliography

Andrew, C. (ed.), Codebreaking and Signals Intelligence (London, 1986).
Drea, E. J. , MacArthur's ULTRA: Codebreaking and the War against Japan (Lawrence, Kan., 1991).
Hinsley, F. H. , et al., British Intelligence in the Second World War (London, 1979–90).
Kahn, D. , The Codebreakers (London, 1973).
Smith, M. , The Emperor's Codes (London, 2000).