After the invasion of Poland of 1939, the ZHP, many of whom joined defense militias, were branded partisans and criminals by Nazi Germany, who had executed many Scouts and Guides, along with other possible resistance leaders (for example during the Katowice massacre). Nonetheless, the ZHP carried on as a clandestine organization. In 1940, the Soviet Union executed most of the Boy Scouts held at Ostashkov prison.