The German overrunning of their country in 1939 did not crush the Polish spirit. Many escaped to the West to carry on the fight. Polish fighter pilots played a major role in the Battle of Britain, while Polish ground forces helped to liberate Western Europe. Another Polish force, held captive by the Russians in Siberia, made an epic trek to the Middle East to fought in Italy, where their courage brought a victorious end to the bitter battle for Monte Cassino.