 In 1943, Princen was arrested by the German occupation authorities in Maastricht, while trying to get to Spain – from where he intended to travel to Britain and enlist in an Allied army fighting the Nazis.He was convicted by the occupation authorities of "attempting to aid the enemy" and in early 1944 was sent to the notorious Vught Camp.On D-day, he was transferred to the "Kriegswehrmachtgefängnis" (Wehrmacht Military Prison) at Utrecht.