Written by Daniele-Hadi Irandoost

The publication of F.W. Winterbotham’s The Ultra Secret claims that Ultra – the codename given to the signals intelligence gathered at Bletchley Park – shortened World War Two by some certain period. In this regard, the author of the official history of British intelligence, Sir Harry Hinsley, stated that Ultra shortened the war ‘by not less than two years and probably by four years’. Be that as it may, such a statement does not embody the variety of other factors that supported signals intelligence towards the Allied victory. As such, I aim to address the broader context comprising the most significant elements around signals intelligence in World War Two: videlicet, alternative sources of intelligence, industrial and manpower strength, along with overall leadership.

Firstly, however, it goes without saying signals intelligence (SIGINT) in military affairs is primarily used to reveal enemy intentions, movements, locations, resources, strengths and weaknesses (ie order of battle), and sometimes to confirm the success of deception operations. Indeed, for all the above purposes, signals intelligence usually delivers more reliable and more valuable information in regular and considerable quantities – thusly raising certainty by reducing the so-called ‘fog of war’ – in ways other sources of intelligence typically cannot. 

So stated, to mention two relevant campaigns, SIGINT was both crucial in the Battle of the Atlantic and the North African Campaign. In the former, the decoded U-boat (submarine) messages enciphered by the Enigma machine led to vital information about German plans, numbers, rendezvous times and locations, which allowed the British to guide convoys away from U-boats, and therefrom reduce the level of ship losses to a bearable level. Assuredly, this gave some breathing space for the development of anti-submarine warfare techniques (which turned the tide of war against U-boats in 1943), and radically lessened one of the most serious effects of the blockade on the nation’s domestic morale. 

Otherwise speaking, in the Mediterranean theatre, signals intelligence contributed to the disruption of enemy supplies by revealing the precise schedule and location of ships travelling across the sea to North Africa. As a matter of course, signals intelligence resulted in the destruction of 60 per cent of enemy ships, in one instance, which happened to take place roughly before the decisive victory at the Battle of El Alamein.

Having said that, it is noteworthy that SIGINT ultimately functioned amidst a wider intelligence apparatus, consisting of human intelligence (HUMINT), aerial reconnaissance, open-source intelligence (OSINT), along with covert action (by the Special Operations Executive). Illustratively, in this relation, the scientists in Bletchley Park were only successful in breaking the Enigma machine because of the intelligence, specifically HUMINT, provided by the Polish, whilst aerial reconnaissance proved useful in the North African Campaign by solving missing pieces or confirming information collected via signals intelligence. 

Conversely, in another example, the surprise attack at the Battle of the Bulge – when Ultra was solely relied on – signals intelligence failed to forecast a major German offensive. Similarly, before the Battle of the Kasserine Pass, signals intelligence did not indicate a surprise attack by Rommel from the southern flank, because it dominated decision-making, despite more accurate evidence from aerial reconnaissance. Such cases, put together, demonstrate that where there was coordination between SIGINT and other sources, consumers met success, and where there was exclusive reliance on one source of intelligence, one faced failure.

Although the above-mentioned sources intelligence played a joint role in relation to the final Allied victory, intelligence is ultimately a ‘tool’ that optimises the use of resources (industrial and manpower) by assisting decision-making and planning at the strategic level. In this sense, intelligence is an indirect ‘auxiliary’ element in war-making, suggestive of the fact that intelligence on its own cannot make war, and that, at the end of the day, wars and battles are won by guns, soldiers, brains and will. In other words, however accurate intelligence may be, it can neither be employed without force or be set up as a (defensive) ‘shield’. By way of illustration, it is hard to forget that despite being the first to break the Enigma machine – ie before the codebreakers in Bletchley Park – the Polish remained vulnerable to any attack as they had little military capabilities for self-defence.

Last, but no less important, the various successes should equally be attributed to coherent planning, proper organisation and coordination by the Allied leaders (eg General Eisenhower in Europe and Field Marshal Montgomery in North Africa) of the use of resources, manpower and intelligence. Put differently, the best of intelligence material could not have been used to their benefit, if the Allied leaders had not applied intelligence appropriately. Indeed, when the Allies started to put their military efforts together through proper coordination between the Eastern and the Western fronts, the result was a division of German forces between both fronts, which inevitably undermined their overall effectiveness.

All things considered, there has been a tendency amid former ‘writer-codebreakers’ from Bletchley Park (like F.W. Winterbotham) to glamorise the significance of Ultra in influencing the outcome of World War Two. Nevertheless, while SIGINT typically supplied a reliable and constant source of information, when put in context it was only central in shortening the war because of its intimate correspondence with other factors, in parallel: namely, as highlighted, supplementary sources of intelligence, manpower as well as industrial capabilities, not to mention proper decision-making (ie planning and coordination) at the strategic level. Ultimately, this noted, it must never be omitted that intelligence cannot win wars on its own. Yet, that the post-war era has seen heavy investment in SIGINT by nations, resulting in sophisticated and gigantic institutions like the National Security Agency (NSA) in America and Government Communications Headquarters (GCHQ) in the UK is not surprising, either way.


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Daniele-Hadi Irandoost is a PhD Candidate at the Department of War Studies, King’s College London, wherein he researches the effective oversight of the British security agencies by the Intelligence and Security Committee. Previously, he graduated from Aberystwyth University in BScEcon International Politics and Intelligence Studies, MA Intelligence and Strategic Studies and PGCE History, whilst holding a second master’s in Philosophy of Education from UCL Institute of Education. Upon his graduation, Daniele was awarded the Ken Robertson Prize in Intelligence Studies for achieving the highest academic mark within the course, whereas, in his spare time, he curates and organises TEDxLambeth annual events. He is an elected Fellow of the Royal Society of Arts.

Image credit: A. Carty, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

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