In last week’s column, I told of Abwehr officer (German intelligence officer) Herman Giskes, head of Abwehr Section IIIF, who set his mind to capturing British agents who were either dropped by parachute into Holland or landed by boat.

This was his plan: the Abwehr should concentrate on trying to locate any transmitters used by any existing agents using detector vans fitted with radio receivers and directional antennae. Once a transmitter was located, they should listen to and copy the messages exchanged between the agent and London-based Special Operations Executive (SOE), the organisation that trained and dispatched the agents. After a short period, arrest the agent and try to make him act as a double agent, whereby messages to SOE would continue but their content would be controlled by the Abwehr.

Giskes was enormously successful and soon a large quantity of weapons, money, radios and the like were being dropped into Holland, all intercepted by Giskes. This became known as Operation Nordpol. He gradually replaced the double agents with German operators and nobody was the wiser, except for Leo Marks, who worked for SOE. It was the task of Marks to teach the agents, before they were dropped in German-occupied countries (France, Belgium, Holland, Norway, et cetera), how to encode messages using a cipher. The ciphers were fairly simple (which upset Marks), as was the encoding.

But sometimes the agents in the field would make a mistake in their coding. The message SOE then got would be indecipherable. It would be normal practice to ask the agent to recode and retransmit the message. However, this would put the agent in danger of being detected. Thus, Marks set up a whole office of women to examine indecipherable messages and find out which mistake the agent had made and render the message understandable. The office had a fair stream of ‘indecipherables’, but none from the agents in Holland. Marks was puzzled by this and finally concluded that the only explanation was that the coding was being done by experts, that is, the German army signals staff.

He revealed his fears to the SOE staff, who ‘ran’ the Holland agents and they dismissed his thoughts – no, they said, the Holland agents are good and solid. In point of fact, the agents’ messages were often out of date or well known; for example, telling SOE that the XX Panzer division was in Amsterdam was low-grade intelligence, since this information was known from air reconnaissance anyway.

But Marks persisted. He sent an ‘indecipherable’ to an agent in Holland, expecting that SOE be asked to repeat it. This did not happen. So, Marks knew that the German signallers must have unscrambled it themselves, which an agent would not be able to do. He set a trap. He noted that German field signallers would end a message with ‘HH’ (meaning ‘Heil Hitler’) and the other operator would instinctively respond HH. So, in a communication, he had the SOE operator send an ‘HH’. Back came, ‘HH’. But still the SOE staff would not accept this – possibly, if it were true, it would be a disaster on a massive scale.

Finally, two agents escaped to London and Giskes’ game was up. He sent the SOE chiefs a message which must have given him great satisfaction: “To [the SOE section chiefs] In the last time you are trying to make business in Netherlands without our assistance stop we think this rather unfair in view of our long and successful cooperation as your sole agents stop but never mind whenever you will come to pay a visit to the Continent you may be assured that you will be received with the same care and result as all those who you sent us before stop so long.”

Operation Nordpol was over.