After the Warsaw Uprising of 1944 started, he reported for duty defending his homeland in the Sekcoin forests. In the aftermath of the Second World War, he helped other citizens in removing the rubble and reconstructing the destroyed city. Jan has also assisted in rebuilding the Ursus factory, where he was employed (department of mechanics) as a tracer, modeler, and caster specialised in many branches of this profession (e.g. metal casting, sand casting). After a few years he was given a master's degree in metal casting.