Summer 1937. What could be more fitting in the cool afternoon of an English country lane than a group of cycling tourists steadily pedalling their way from one historic site to another, stopping to camp overnight in fields along the way.
The only problem was, that summer, some of those groups of teenage boys were Hitler Youth.
In an era without satellite photography, when detailed ordnance survey maps could be hard to come by and when tension in Europe was rising, MI5 were worried that this innocent cyclo-tourism was a cover for spying.
MI5 had been told that Hitler Youth groups visiting abroad were asked to complete a detailed questionnaire, including questions on terrain, population, and political views of the population.
Hitler regarded his youth movement as the kernel of an Aryan 'master race'
They were asked to take photographs, especially of industry, and to get lists of names of all those taking part in anti-German movements.
In May 1937, the British "Daily Herald" paper had printed an article about "spyclists" - based on translation of the Nazi Cycling Association's advice to members travelling abroad.
It too asked travellers to try to note carefully the features of the countryside they visited:
"Get into your head all landmarks like steeples and towers and all fords and bridges and acquaint yourself with them in such a way that you will be able to recognise them by night"
And one of the senior figures in the Hitler Youth had moved to London at the start of the year, ostensibly to study. MI5 suspected that Joachim Benemann's real object however was to develop the Hitler Youth in the UK.
Local papers speculated on the real reason for the visits
On an earlier visit, undertaken in 1934 and 5, he had set up joint Anglo-German youth camps, one at Bryanston School, and he had tried to develop links between the Hitler Youth and the Boy Scouts, without much success.
So the head of MI5, Colonel Sir Vernon Kell, decided to try to track visiting Hitler Youth cycling groups. Chief Constables were asked to monitor them, to try to find out what their planned routes were, without questioning the leaders.
From the file, it appears they identified seven substantial groups, each of about twenty young men. These were generally the older members of the Hitler Youth: in their late teens or early twenties.
Their itineraries were usually built round visits to the great English historic sites - Oxford, Cambridge, London. Though one party was touring Scotland and another finished in Wales.
MI5 did not shadow the cyclists closely, so it is not recorded exactly where they stayed and who they met. There was some reporting in local papers though: the Boston and Spalding Free Press reported that the Spalding Rotary Club laid on a special dinner for one group, who thoroughly enjoyed their sausages and mash, and charmed the local people with their good manners.
The Hitler Youth who travelled to Britain had been specially selected - a number had even had been to training camps before the visit.
Some of them met or shared camps with British Boy Scout groups. The most striking was the Tamworth Scout troop - for whom this was a return visit. They had already been guests of the Hitler Youth in Hamburg earlier in the summer, thanks to their very pro-German Scoutmaster.
It was like a Roman legion
Les Fardon, former Boy Scout
They had stayed at a Hitler Youth camp and even taken part in a torchlight rally. One of the boys, Les Fardon, told Radio 4's Document Programme ten years ago: "It was like a Roman legion," he said. "You had these long banners and you were marching to tune... it was very stirring and frightening"
Another of his fellow Scouts remembered it as being a very exciting trip, and he recalled how even the British boys fell into doing the "Heil Hitler" salute. "They liked you to do it," he added. Both boys made friends with some of the Germans.
When the Hitler Youth came to visit them, it proved controversial, and prompted intense debate in the pages of the local paper, the Birmingham Post. The head of MI5 asked to see the letters. The most pro-German was R. Charles Lines who wrote about the farewell supper for the Hitler Youth:
"Many remarks passed to me by Tamworth residents showed very plainly what a wonderful impression these boys have made during their stay. There is no doubt that Tamworth has thoroughly enjoyed entertaining them and I know how splendidly local people have risen to the occasion"
Which prompted a tart response from another correspondent, "WFA", who wrote: "Is it not easily understandable that when one has first hand information of the persecution and cruelty meted out by youthful Nazis at home, one is suspicious of their perfect behaviour abroad. One is bound to ask oneself "is it a confidence trick?"
The charm offensive was being carried out at a far higher level too. In November 1937 Lord Baden Powell met the Chief of Staff of the Hitler Youth at the German Embassy. The elderly Chief Scout had long been an admirer of the Hitler Youth, and was keen to develop closer links.
Baden Powell was asked if he would visit Hitler personally, and did not demur, telling the Germans that he was "fully in favour of anything which would bring about a better understanding between our nations"
The British government stepped in to stop that though. A note on the file shows that Lord Cranbourne, Under Secretary of State for Foreign Affairs, called Lord Baden Powell's chosen successor, Lord Somers, around a fortnight later. He "strongly deprecated" close relations, runs the note.
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