Ka cika wannan magana: A watan Mayu na shekara ta 1940, Nazi na Jamus sun mamaye Belgium. Bayan mika wuya na Belgium da farkon mamayar Jamus, shugaban POB<unk>BWP Henri de Man ya sanar da rushewar jam'iyyar gurguzu a matsayin wani ɓangare na manufar haɗin kai. Van Acker ya yi ritaya daga rayuwar jama'a. A cikin 1941, duk da haka, ya koma cikin jam'iyyar gurguzu ta haramtacciyar jam'iyya da kuma kungiyar kwadago ta karkashin kasa a karkashin "nom de guerre" "Monsieur André" kuma ya zagaya kasar yana tuntuɓar sassan jam'iyyar. A cikin
Bayan 'Yantar da Belgium a watan Satumbar 1944, Van Acker ya fito a matsayin shugaban jam'iyyar magajin POB<unk>BWP, Jam'iyyar Socialist ta Belgium ("Belgische Socialistische Partij", PSB-BSP).