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During the four years of World War I, the Secret Service Bureau was in the front lines of the fight against German espionage. However, when the UK entered the war in August 1914, the entire Bureau consisted of only fifteen members of staff.
It was mobilised as a branch of the War Office under the Directorate of Military Operations (which still exists within today's Ministry of Defence, the successor to the War Office). It came under the branch known as MO5, which was subdivided into eight sub-sections. Its chief, Major Vernon Kell, was given responsibility for MO5(g).
MO5(g) was renamed as MI5 in January 1916 and was incorporated into a new Directorate of Military Intelligence. (See What's in a Name? for a summary of these changes of name.)
Wartime legislation increased the responsibilities of MI5 to include the co-ordination of government policy concerning aliens, vetting and security measures at munitions factories. MI5 also began to oversee counter-espionage measures throughout the British Empire.
Image of a propaganda poster "Once a German, always a German!" Anti-German views led to thousands of innocent people being falsely accused of spying.
As is still the case today, MI5's role was advisory rather than executive, and its officers could not detain suspects. The police, acting on information from MI5, performed the task of arresting enemy agents. Many suspects were personally interrogated by Sir Basil Thomson, Assistant Commissioner of the Metropolitan Police, in his room at Scotland Yard. MI5 officers were present but the police appear to have held the responsibility for the proceedings.
The task of identifying genuine German agents was complicated by an intense atmosphere of anti-German hysteria across Britain. The Germans were reviled publicly as "Huns" and were accused - with much exaggeration -of having committed widespread atrocities in the territories that they occupied. Serious anti-German riots broke out in several British towns and cities. Shops owned by Germans and Austrians were attacked and looted by angry mobs that sometimes numbered thousands of people.
In this climate, many innocent people were falsely denounced as spies. Their bona fides had to be investigated and confirmed by the police and MI5. This was an extremely time-consuming task, requiring a massive increase in MI5's manpower, which stood at nearly 850 by the end of the war.
The vast majority of those investigated turned out to be entirely innocent. Assistant Commissioner Sir Basil Thomson later recalled that "at least nine out of every 10 persons who might otherwise have been detained under suspicion for an indefinite period were cleared of all suspicion."
Even so, there were some genuine German spies in the country. MI5 was highly successful in identifying them and preventing the Germans from making significant intelligence gains against UK targets. 35 enemy agents were captured during the course of the war and eleven were executed by firing squads at the Tower of London. The cases of Carl Hans Lody and Carl Friedrick Muller were particularly noteworthy and caused much comment at the time. See below for more information on these cases.
By the war's end in November 1918, MI5's chief Vernon Kell had been promoted to the rank of Colonel. He was knighted in 1920 in recognition of his services to the country.
Photograph of Carl Hans LodyCarl Hans Lody
In October 1914, a German by the name of Carl Hans Lody was arrested in Killarney, Ireland, on suspicion of espionage.
He was charged with "war treason" and was imprisoned in the Tower of London. He was the first person to be incarcerated there for nearly a century.
A few weeks later, he was brought before a British military tribunal in London which was described at the time as "a Court-martial unique in the modern history of this country."
The court heard that Lody was in fact a senior lieutenant in the German Imperial Navy. He had falsely acquired a United States passport on the outbreak of war, using the alias of Charles A. Inglis. He had subsequently toured England, Scotland and Ireland to gather militarily useful information. He admitted that he had acted out of "patriotic German motives" in coming to the UK.
Lody was convicted and on 6 November 1914 he was shot at the Tower's rifle range by an eight-man firing squad drawn from the 3rd Battalion The Grenadier Guards. He was the first foreign spy to be executed in Britain, and the first person to be executed at the Tower for over 150 years.
After the Nazis took power in Germany in 1933, Lody was adopted as a German national hero. The German Navy commemorated him by naming the destroyer Hans Lody after him in 1935 (ironically, the ship was surrendered to the United Kingdom following the Second World War). A memorial to Lody can still be seen in the German city of Lübeck, on the Burgtor gate.
Photograph of Carl MullerCarl Muller
Carl Friedrick Muller was among a number of German agents arrested during 1915. Muller was recruited into the German Secret Service some time in late 1914. Sailing from Rotterdam in the neutral Netherlands, he entered Britain via Hull in January 1915.
He subsequently travelled to London, where he wrote a number of letters (in English) to various parties, some sent via a British-born man of German descent called John Hahn.
The British authorities intercepted all of the letters. They appeared innocuous at first, but it was discovered that they contained messages in German written in invisible ink - made from formalin (formaldehyde) and lemon juice - between the lines of the English text.
Muller and Hahn were arrested in February 1915 and brought to trial in June. Hahn pleaded guilty to charges of espionage and was sentenced to seven years' imprisonment. Muller pleaded not guilty, but was convicted and sentenced to death. On 23 June 1915, he was taken to the firing range at the Tower of London and shot.