Hartmann was also a member of the young communist resistance group "Der Soldatenrat", named after the that had emerged in Germany after the previous "world war". Other members of the group included , Leopoldine Kovarik and . All of them, like Hartmann, would have been sentenced to death and executed by the time the war ended. The group had their own "underground" newspaper, dedicated to urging military conscripts and others in the army to desert the German army and cross over to join the Soviet army. It was Hartmann who composed the letter - described in some sources as a leaflet - that she addressed to members of the army She organised the large scale production of copies and co-ordinated their distribution. An early attempt to distribute the missives using the failed when they were blocked. It turned out that the key to unblocking the mail service was to be able to identify each individual soldier by his unique "military mail reference number" ("Feldpostnummer"). By this time her partner, Rudolf Masl, was in Norway, having been conscripted for military service on the frontline. He was able to obtain and pass on the necessary individual reference numbers for more than a thousand serving soldiers. These he handed over when he was briefly home on leave in Vienna in the Autumn/Fall of 1941.