The high point of MO5(g)’s counter-espionage operations came in June 1915, when seven German spies were rounded up in little more than a fortnight.83 Thereafter, German intelligence operations in Britain were drastically scaled down. German archives show that the number of agents in Britain declined from twenty-two in January 1915 to only four at the end of the year.84 For the remainder of the war Germany relied largely on brief visits by bogus commercial travellers from neutral countries who carried as much information as possible in their heads rather than on paper. They had little success. Kell’s Bureau (renamed MI5 in January 1916) concluded that most had neither the aptitude nor the training required for successful espionage. The last to be executed was Ludovico Hurwitz y Zender, a Peruvian of Scandinavian descent who aroused the suspicions of the censors by sending bogus orders for large quantities of Norwegian sardines at the wrong season, and was shot in the Tower on 11 April 1916.85
Shortly after Hurwitz y Zender’s execution, MI5 recruited its most successful double agent of the war, an American in Holland codenamed COMO, described in what remains of his file as ‘working in Holland as a German Agent, but double-crossing for us’. In May 1916 COMO was sent to Britain by the Kriegsnachrichtenstelle to look up agents who had been out of contact for some time. He reported to MI5 that the first of those he contacted, Fritz Haas, was ‘harmless and probably never an agent, if so unknowingly’. In July COMO was sent on a second mission to obtain intelligence on Canadian troops in England and when they were likely to be sent to France, as well as details of British naval losses at the battle of Jutland. According to an MI5 note:
We gave ‘COMO’ information about our Canadian Divisions – their numbers and positions, etc – at places not obviously incorrect, and gave particulars of their numbers etc, as would make them plausible. Also, fictitious information of Naval, Industrial and Political situation, most convincingly written. Also sent information regarding the effects of the Zeppelin raids on London.
In September, on MI5 instructions, COMO sent further disinformation on the military situation in England and likely movements on the Western Front. He told the Germans that the British were planning an attack on the Belgian coast on the 15th. COMO continued to pass on at irregular intervals details of the intelligence missions entrusted to him by the Kriegsnachrichtenstelle, and MI5 continued to channel disinformation through him. According to a post-war summary, COMO ‘was always quite honest and trustworthy and did some v[ery] valuable work for us, at the same time holding the German’s [sic] confidence’. War Office nervousness, however, prevented the development of a full-blown Double-Cross System. On at least one occasion, the Director of Military Intelligence described the questions put to COMO by the Kriegsnachrichtenstelle as ‘extremely dangerous’, and instructed that ‘no answers could be given’.86
The final attempts by German intelligence to establish a significant agent network in Britain were based on the recruitment of Americans. On 3 June 1916 Tinsley in Rotterdam supplied MI5 with a cover address in The Hague used by German intelligence, which Kell immediately ordered to be put under censorship.87 This was reckoned by MI5 to be ‘one of “T’”s best efforts’,88 since it led to the discovery of an ‘important gang’ of spies run from New York by Karl Wünnenberg, a German naval reserve officer, and the journalist Albert Sander.89 To strengthen their cover in New York, Wünnenberg and Sander had no contact with German officials in the United States and were run by the Antwerp Kriegsnachrichtenstelle. They succeeded in recruiting six US journalists to work as agents, paying each up to $1,000 in advance and promised another $125 per week.90 The large sums offered are an indication of how short of agents in Britain the Kriegsnachrichtenstelle had become.
On 29 September 1916 the censors opened a letter written from England a week before by one of the US journalists recruited by German intelligence in New York, George Vaux Bacon, to the German intelligence address in The Hague identified by Tinsley. There was a further delay before Major Carter of MI5 examined the letter on 9 October, by which time Bacon had been in Holland for over a fortnight and realized his letter had been delayed by censorship. Bacon’s suspicions were further aroused when he was approached, ‘somewhat clumsily’ in MI5’s view, by one of Tinsley’s agents. Though MI5 believed that Bacon ‘suspected that the British authorities were on his tracks’, he none the less returned to Britain on an espionage mission early in November. MI5 noted that he had a ‘loose’ (promiscuous) lifestyle, but ‘nothing suspicious’ was found in his possession on his arrival and he managed to ‘elude his watchers’ while visiting naval bases in Ireland. On 9 December 1916 Bacon was interviewed at Scotland Yard, not with the expectation of persuading him to confess to espionage but in the hope that he could be ‘frightened out of the country’. However, this time enough incriminating material was found in his possession for him to be kept in custody. In addition to equipment for secret writing, ‘two of his socks were found to produce invisible ink when soaked in water’.91
Two days later, MI5 received what it considered ‘information of the utmost importance’ in the Bacon case from an American journalist, Roslyn Whytock, who became the second wartime German agent recruited for espionage in Britain to operate as a double agent.92 Whytock had a colourful background. Before the war he had been both a newspaper editor in St Louis, Missouri, and a captain in the Missouri National Guard, but had to resign his commission after an affair with a local fashion model, Mrs Irma Jones, whose husband cited him as co-respondent when obtaining a divorce. Whytock appears to have possessed exceptional social skills. According to an ‘exclusive’ interview in the New York Times with Mrs Whytock, who also sued for divorce, Mrs Jones’s husband came to St Louis ‘for the purpose of killing Whytock, but the Captain talked him out of it, and they became chums in a few days’.93
Early in November 1916 Whytock reported to the MI5 Military Control Office in New York that the German agent Albert Sander was trying to recruit him to work as a spy in England. At the Control Office’s request, Whytock pretended to accept Sander’s offer but revealed all he knew to MI5 once he reached England, including the codes and secret inks used by the ‘gang of American spies’ and the identity of ‘a disreputable US journalist’, Charles Hastings, with whom Sander had told him to collaborate. Whytock explained that, probably in an attempt to improve security and outwit the censors, Sander had given instructions for his journalist agents to work in pairs. One was to collect intelligence in England, then transmit it by letters in invisible ink to his partner in Holland, who would pass it on to the Kriegsnachrichtenstelle.94 There Whytock’s role seems to have ended. No attempt appears to have been made by Kell, as it would have been in the Second World War, to continue to use him as a long-term double agent. Whytock’s experience of working for MI5 was, however, later put to good use. After the United States entered the war in April 1917, he became a captain in the US Army Intelligence Service in New York.95
Influenced no doubt by Whytock’s revelations about the ‘gang of American spies’, Bacon was persuaded on 9 February 1917 to make what MI5 considered ‘a full confession’ about his recruitment by Wünnenberg and Sander. At a court martial in the Guildhall on 4 March Bacon was sentenced to be shot by a firing squad at the Tower.96 Washington, however, persuaded the British authorities to commute the sentence to one of life imprisonment and send Bacon to the United States to give evidence against his German spymasters. Late in March a New York court sentenced Wünnenberg and Sander to two years’ penal servitude in a federal penitentiary. Judge Van Vleet himself sentenced Bacon to one year’s penal servitude, but lamented that ‘he disliked it very much to send such a bright young man to the penitentiary.’97
In the early months of 1917, as part of a policy to expose the operations of German intelligence in the United States, the DNI, Blinker Hall, with the approval of the First Lord of the Admiralty, Arthur Balfour, set out to shock Americans by publicizing the ‘Zimmermann telegram’ (decrypted by British codebreakers), which expressed secr
et German support, if the United States entered the war, for the Mexican reconquest of ‘lost territory in Texas, New Mexico and Arizona’. Balfour said later that the moment when he handed over the decrypted telegram to the US ambassador in London was ‘the most dramatic in all my life’.98 President Woodrow Wilson’s celebrated speech to a joint session of Congress on 2 April calling for a declaration of war on Germany cited both its intelligence operations in the US and the Zimmermann telegram as evidence that ‘Germany’s irresponsible government . . . is running amok’:
One of the things that has served to convince us that the Prussian autocracy was not and could never be our friend is that from the very outset of the present war it has filled our unsuspecting communities and even our offices of government with spies and set criminal intrigues everywhere afoot . . .99
Though Wilson doubtless had chiefly in mind German sabotage operations (discussed below), the sentencing only a week earlier of Wünnenberg and Sander, and the evidence of their corruption of ‘such a bright young man’ as Bacon, served as a recent reminder of the German spies at work in the heart of New York.
Surviving MI5 archives contain details of sixty-five German agents who were arrested and convicted or imprisoned under the Aliens Restriction Act during the First World War.100 German archives indicate that a total of at least 120 agents were sent to Britain at some point between 1914 and 1918.101 Some (perhaps a majority) of the unarrested agents appear to have been ‘reconnaissance agents’ visiting British ports, whose access to intelligence was limited to what they could observe themselves.102 A probably significant minority also broke contact with German intelligence after arriving in Britain. MO5(g) counter-espionage successes and the execution of convicted spies persuaded an unknown number to follow the example of Walter Rimann in 1914103 and flee the country, or else to give up espionage. On at least two occasions the double agent COMO was asked by the Antwerp Kriegsnachrichtenstelle to track down German agents who had broken contact. He reported to MI5 in October 1916 that:
The Germans had lost track of about 20 of their agents whom they had sent to England, and could not understand what had happened to them. COMO said he satisfied their curiosity by saying they had gone across to America after receiving their £20 from the Germans, and said [the Germans] should not pay them until they had completed the work they had been sent to England to do.104
Though some active wartime German spies were not detected by MO5(g), no convincing evidence has yet emerged to show that any sent back significant intelligence.105
MI5’s post-war assessment of its counter-espionage operations concluded:
If there is any single standard by which to measure the success of the Bureau, it is the level attained by the wages paid to the enemy’s agents; and in the case of Great Britain, we know that, whereas at the outbreak of war £10 to £25 a month was the normal figure, it rose rapidly to £50 in 1915, to £100 about June 1916 and, by the beginning of 1918, to £150 a month. In the last year or so before the Armistice, a good spy could get practically what he chose to ask for.106
MI5 attributed much of its success in dealing with German espionage to good preventive security (later called ‘protective security’) which had turned Britain into a hard target:
It is apparently a paradox, but it is none the less true, and a most important truth, that the efficiency of a counter espionage service is not to be measured chiefly by the number of spies caught by it. For such a service, even if it catches no spies at all, may in fact perform the most admirable work by hampering the enemy’s intelligence service, and causing it to lose money, labour, and, most precious of all, time, in overcoming the obstacles placed in its way. One must bear in mind the immense and rapid success of the Prussians in a campaign like that against Austria in 1866, when the Austrians had no C.E service, and when therefore spies all over Bohemia were able to report every movement of the Austrian troops, in order to fully realise the value of organisations like those of the censorship, the port controls and the other preventive machinery put in place by the S[pecial] I[intelligence] B[ureau].107
One measure of the success of protective security was the lack of German sabotage in Britain. At the outbreak of war, it was entirely reasonable for Kell and Whitehall to take the threat of sabotage very seriously. General Staffs throughout Europe, as well as some leading military writers, had predicted that modern warfare would involve civilians acting as sabotage agents.108 Kell shared those fears. As research in German archives confirms, Kell’s fears were well founded. The German military intelligence department, run by Lieutenant Colonel Walter Nicolai, established a special department (Sektion P) to perform sabotage operations in Allied countries (Agitat-Werke) and prevent delivery to the Allies of essential supplies from the United States. Sektion P placed explosives, often disguised as coal briquettes, on several transatlantic ships in North American ports.109 None, however, was successfully placed on ships in British ports.
Sektion P’s most notorious act of sabotage was at a depot in Black Tom Pier, New Jersey, which contained over 2 million pounds of ammunition destined for a Russian offensive on the Eastern Front. On the evening of 30 July 1916 the depot was blown up, killing four people and causing $14 million worth of damage. The explosion was so powerful that the shockwaves could be felt as far as 90 miles away. An official American inquiry into the explosion after the war implicated several former members of the German intelligence services.110 Had security in Britain been as ineffective as in the United States, German sabotage would probably have been on at least the same scale.111 The fact that there seems to have been no attempted Sektion P operation in Britain remotely similar to the Black Tom attack owes at least something to the ‘physical security’ measures organized by Holt-Wilson, with central and local government authorities, which established prohibited zones around sensitive locations, such as munitions dumps, throughout Britain.112
In August 1915, one year after the outbreak of war, there was a major expansion of protective security. A new Port Control section (E Branch) was founded to control civilian passenger traffic to and from the UK, in collaboration with Military Permit Offices in London, Paris, Rome and New York.113 The Military Permit Offices abroad worked closely with British consular and MO5(g) officials in issuing entry visas and monitoring British citizens abroad. Military control officers (MCOs) from MO5(g) at designated wartime British ports of entry and frontier stations in the Empire worked with aliens officers and police, and had the power to refuse entry of those considered undesirables.114 Among those MI5 officers who questioned foreign travellers at British ports was Hinchley Cooke. The MCO at Falmouth, Major Rowland Money, reported to Kell in October 1916 that Hinchley Cooke, still only twenty-two, was ‘very keen on port work. His languages have been most useful as we have a number of German women in transit through Falmouth.’115 While questioning the German women and others Hinchley Cooke seems to have posed as a German named Wilhelm Eduard Koch, who they must have assumed had changed sides.116 His skill in interrogation led to a number of operations over the next two years in which he also posed as a German. Hinchley Cooke’s record of service contains a number of photographs of him in German army uniform as well as a 1917 Metropolitan Police Alien Enemy Certificate of Registration card in the name of Wilhelm Eduard Koch, which used the same photograph as his War Office identity document.
The main contribution of MI5 Port Control was to protective security. As the capture of the German sabotage agent Hans Boehm on landing in England in January 1917 demonstrated,117 Britain was a hard target. The most novel as well as the most sinister form of wartime sabotage attempted by Sektion P was biological warfare. At least one of its scientists in 1916 devised a scheme to start a plague epidemic in Britain, either by infecting rats or, more improbably, by dropping plague bacilli cultures from Zeppelins over ports. The Prusso-German General Staff, however, vetoed bacteriological warfare against humans as totally contrary to international law (the Hague Laws of Warfare). No such restrictions applied to a
nimals. The German General Staff considered that the contamination of horses, cattle and other livestock was an attack on ‘military supplies’, which was permissible under the Hague Laws. This was highly significant considering the important – and nowadays often underrated – role performed by horses and other livestock in the First World War. In April 1915 Sektion P sent Dr Anton Dilger, a US citizen of German parents and Heidelberg-trained physician, to the United States. At a laboratory in Washington DC, Dilger produced cultures of bacillus anthracis and pseudomonas mallei, the causative agents of anthrax and glanders. A few months after Dilger’s arrival in Washington, the cultures were administered to horses and mules awaiting export to Europe in holding pens at docks in New York, Baltimore, Newport News and Norfolk, Virginia.118 The US programme ended in the autumn of 1916, after Dilger’s return to Germany. There is some evidence to suggest that Sektion P then attempted to spread anthrax and glanders to Britain as well. On 30 March 1917 MI5 and the Special Branch circulated an intelligence warning to other government departments concerning evidence that German agents were attempting to infect horses and mules in Britain with anthrax and glanders. Four outbreaks of anthrax on the Isle of Man a month later were almost certainly the result of German biological warfare.119 But for protective security there would probably have been many more outbreaks. The last German sabotage agent to reach Britain in the course of the war was Alfred Hagn, arrested in May 1917 with the help of intelligence leads from the Norwegian security service.120 After the death sentence (later commuted) was passed on Hagn in August, there were no further trials of German agents for the remainder of the war.
A post-war report on preventive security concluded, with a degree of overstatement, that MI5 could claim to have made ‘some difference, great or small, to the life of almost every inhabitant of the United Kingdom’:
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