1939 German invasion of Poland

German soldiers march past structures in foreground, which are probably tank traps, during German invasion of Poland / soldiers lift barricade gate; mounted soldiers ride through / Polish soldiers run across field / rear shot montage German soldiers fire artillery after officer gives order / rear shot three German soldiers in trench in countryside; explosions occur in background / soldiers look out of trench using field glasses and periscope / WS German artillery fires / explosion near stopped train on small rise / from Greatest Headlines of the Century series / Note: [exact dates not known]