Pedzisa mutsara unotevera: Muna May 1940, Belgium yakapinda neNazi Germany. Zvichitevera kukundwa kweBelgium uye kutanga kwekugara kweGerman, mukuru wePOB<unk>BWP Henri de Man akazivisa kuputswa kwebato rezvematongerwo enyika sechikamu chemutemo wekubatana. Van Acker akasiya upenyu hwevoruzhinji. Muna 1941, zvisinei, akabatanazve nebato risiri pamutemo rezvematongerwe enyika uye sangano rezvematongerwe enyika risingazivikanwi pasi pe "nom de guerre" "Monsieur André" uye akafamba-famba munyika yose achiita kuonana nezvikamu zvebato. Pa
Kusunungurwa kweBelgium munaGunyana 1944, Van Acker akabuda semutungamiri webato rakatevera POB<unk>BWP, Belgian Socialist Party ("Belgische Socialistische Partij", PSB-BSP).