In the last post we talked about how resisters had to rely on their gut instincts or on referrals to judge whether to trust someone. In the case of an escape line such as Dutch-Paris, they had to trust strangers to work with and to help. But it made any resistance network vulnerable.
The German occupation authorities were very aware of this vulnerability among resisters and especially in escape lines. They exploited it expertly and efficiently to infiltrate the networks.

One of the better known ploys used by German military police was to send false aviators through an escape line. The idea was that a German agent would pretend to be a downed Allied aviator all the way through the line to Spain. In Spain he would contact his superiors. (Spain was neutral with a decided partiality for the Third Reich). The German agent would have the names or at least locations of everyone in the escape line.

This is why aviator escape lines desperately needed radio contact with London so they could verify so-called aviators’ identities. Dutch-Paris did not have its own radio link with London, but the Comité in Brussels had a connection with one of the official escape lines (meaning run by SOE) and they shared their radio time. Before the Comité accepted aviators from their hiding places in the Netherlands, Belgium or Northern France, two Dutch-Paris men travelled to the hiding place and interviewed the aviators. They asked them questions like their parents’ names and cultural questions about America (if they were American). They sent the replies to London by radio and were told if the man was actually missing and was most probably who he said he was. Only after that would the Dutch-Paris men bring the aviators to the safe house in Brussels and send them down the line to Spain.

But this system had holes in it. What if the escape line didn’t have radio contact with London? What if Dutch-Paris was asked to take an aviator from a hiding place in southern France? What if the German agent spoke with a flawless American accent and knew all the rules of baseball? Resisters were volunteers, not trained interrogators.

German agents did slip through. When the British caught them, they executed them. Hopefully before the agent was able to betray the entire escape line.