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On June 22 1940, France signed an armistice with Hitler Germany causing about 1.5 million French prisoners of war (POW) being detained in German camps. During the war there were multiple breakout attempts as about 71.000 out of 300.000 French POW’s managed to escape. The local population actively and passively assisted in the escape of these prisoners of war. Among the regions where the local population assisted was the province of Limburg in the south of the Netherlands. This form of subversive activity often appeared spontaneous, however, the people involved realized that the smuggling routes they facilitated were vulnerable. This because it sometimes occurred that smug-gling routes were infiltrated, causing exposure of some of the nodes in the corresponding smuggling network. Therefore the networks were designed such that upon exposure of a node (or upon the arrest of some individuals) other escape routes were available. Hence in the province of Limburg a network of smuggling routes emerged that was designed to efficiently handle the flow of escaping downed aviators and POW’s and at the same time ensure the necessary secrecy. For instance, an escapee that more or less randomly appeared at the German-Dutch border would be assisted by a Dutch farmer (who spoke French). This farmer would guide the POW to the local Church where he would obtain further assistance. If an escapee successfully managed to escape to France he would of-ten try to inform his fellow mates still in the prison camp about the route taken. This assisted the spontaneous emergence of these smuggling networks.

It needs no elaboration that the individuals engaged in setting up and continuing the subversive activities to aid the escape of allied prisoners were doing so by improvisation.

One can argue that network formation occurred according to the evolutionary dynamics of natural selection: those routes that were not discovered and exposed persisted; those that were infiltrated and exposed perished. The structure of the resulting networks therefore is expected to be a balance of the tradeoff between secrecy and information. Therefore we investigate two of those smuggling routes. Since these smuggling networks operated for an extended period of time, the exposure of a node in the network depended on the

centrality of the respective node in the exchange of POW’s. Therefore we will analyze the interior pattern of the smuggling network by comparing the corresponding network structure to the results obtained for scenario 3 in the theoretical framework. That is, we will look at the organization of that part of the network that has to guide the escapees through a certain part of the occupied territory. We will not consider the nodes at which the escapees entered or exited the network because these are typically determined by geographical considerations (such as the existence of waterways and dense forests, etc.).

Often the POW’s were introduced into the network by local Dutch people that worked in Germany or they arrived at certain villages on their own.

Steyl smuggling route

Starting in 1941 chaplain L.A. Akkermans initiated the creation of a smuggling network to aid the escapees arriving in the region of the towns of Tegelen and Steyl [Cammaert, 1994]. He tried to structure the smuggling of POW’s arriving from Germany. Local monasteries functioned as safe-houses. The smuggle route in the region of Tegelen and Steyl consisted of five villages; escapees arrived at Venlo (vn) and were smuggled through Maasbree (ma), Baarlo (ba), Steyl (st) and Belfeld (be) and from thereon routed to Belgium. The theoretical optimal network and the actual network structure are given in the Figures 4.3 and 4.4 below, vn

ma st

ba be

Figure 4.3: The Steyl smuggling route.

vn

ma st

ba be

Figure 4.4: Theoretical optimal smuggling route.

It can be seen that the Steyl smuggling network is close to the optimal network.

Actually, removing the Steyl-Baarlo route would make it optimal. It is known that the German military conducted regular inspections (randomly) but they never disclosed any

4.2 Two empirical examples 53

actual POW being smuggled. The Germans suspected smuggling to be taking place (they arrested at least five people in the region) but were never able to expose the network. It is assumed that about 150 to 250 people were smuggled throughout this region.

Maasbree and Baarlo smuggling route

Several other smuggling routes West of the river Maas comprised of the nine villages Grubbenvorst (gr), Velden (ve), Venlo (vn), Tegelen (te), Steyl (st), Belfeld (be), Baarlo (ba), Maasbree (ma) and Sevenum (se). Again chaplain Akkermans from Tegelen con-tributed to this network. Because of the close proximity of Baarlo to the river Maas a lot of pow’s coming from Steyl crossed this town. The actual (Figure 4.5) and an approximated optimal (Figure 4.6) network structure are shown below.

gr

se ve

ma vn

ba te

be st

Figure 4.5: The Maasbree and Baarlo smuggling route.

gr

se ve

ma vn

ba te

be st

Figure 4.6: The approximate theoretical optimal smuggling route.

The optimal networks in chapter 3 are unlabeled, i.e., there are multiple ways in which such an optimal network can be ‘fitted’ on labeled vertices. Even so, one can wonder how ‘close to the optimal network’ the network in Figure 4.5 actually is. The optimal configuration can be obtained by the ‘actual’ one only by changing 3 routes:

Tegelen-Maasbree to Tegelen-Sevenum, Grubbenvorst- Baarlo to Grubbenvorst - Belfeld and changing Sevenum-Baarlo to Velden-Belfeld.

One caveat is that optimality in both our cases only considers the network structure, i.e., changing the node labels without altering the network structure does not change the degree of optimality of the corresponding network. Hence there are multiple distinct labeled networks that can be obtained by changing only a few links with respect to the optimal ones. This should be taken into account when discussing the relative optimality of a network.