Commonsense tells us that resisters worked in isolation. After all, they were up against the Gestapo. All too easily, the opposite of secrecy in the resister’s world became the torture chamber.

So resisters used false names and safe houses. Many of them worked on a cell system in which they knew only the people most closely involved in their own efforts. Only one person in that cell knew only one person in the next cell. That limited the damage that could be done if someone was captured and tortured into revealing information.
This compartmentalization was so important that two young Dutch women who were friends and students together at the Sorbonne in Paris did not know that they both worked for Dutch-Paris in 1943-1944 until they met at the notorious women’s concentration camps of Ravensbrück.

Yet at the same time, there was a vibrant underground interchange between resistance groups. One reason for this apparent breach of security was that resisters sometimes needed help from other resisters. A resister without the resources to forge documents might have to get false identification papers from a different resistance group that specialized in forgery. Or that group of forgers might find themselves with a downed Allied pilot on their hands and no way to get him to Spain other than contacting an escape line such as Dutch-Paris.

other reason was that resisters were a small minority. Some resisters belonged to more than one network or had a reputation for helping others. Inevitably the work of different groups collided in such individuals.

This active interchange among resisters was particularly obvious with Dutch-Paris because it acted as an escape line and courier network across France and Belgium and into Switzerland, Spain and the Netherlands. It served, in fact, as an international communications system for several local resistance groups, carrying both information and people over borders and out of occupied territory.