In February 1945, a transport with approximately 200 Jewish women reached Porta Westfalica. The women had arrived from the Horneburg satellite camp of the Neuengamme concentration camp. In Horneburg, they had been working as forced labourers for Valvo, a subsidiary of Philips, manufacturing radio valves for the Wehrmacht’s measurement and communications technology. From autumn 1944, there were plans for relocating Philips’ radio valve manufacturing facilities underground to the upper tunnel system of the Jakobsberg.
In the weeks that followed, more female concentration camp prisoners arrived at Porta Westfalica on transports. Most of the Jewish women on these transports had been imprisoned in Auschwitz in 1944. In the late summer and autumn of 1944, the SS had then transferred them from Auschwitz to the satellite camps of the Neuengamme and Groß-Rosen concentration camps. After the evacuation of these camps, they arrived in the region of Porta Westfalica right in the middle of winter after having to march and travel by train in open wagons for weeks.
By the end of March 1945, a total of 967 women were imprisoned on the grounds of the camp located on Frettholzweg in Hausberge. The route which led from the camp to the underground factory known as the Hammerwerke was at least several kilometres long. Numerous women who were on the first transport reported that they had to work and sleep in the mine for weeks on end and therefore did not have access to daylight during this time.