Rubuta ci gaba don wannan sakin layi - Stjernfelt ya kammala karatunsa daga Kwalejin Kwalejin Royal Swedish Naval a 1940 kuma an ba shi izini a matsayin jami'in kuma an sanya shi zuwa Vaxholm Coastal Artillery Regiment a ranar 9 ga Afrilu, da farko an shirya saboda harin Jamus a kan Denmark da Norway. A wannan rana, dole ne ya tattara wani shiri a cikin bakin teku zuwa Stockholm. Tuni a matsayin matashi laftanan, ya zama kwamandan baturi na batirin bindiga a tsibirin Roten a arewacin Tekun Åland, batirin da ya ci gaba da kasancewa cikin shirin yaƙi a duk lokacin Yaƙin Duniya na II. Tun yana ƙarami ya sami sha'awar tarihi na soja. Ba da daɗewa ba bayan ƙarshen Yaƙin Duniya na II
, ya yi tafiya tare da sabon matarsa Borghild tare da bakin tekun Normandy, yana tattara bayanai a cikin ƙasa da kuma daga kwamandojin Jamus waɗanda suka jagoranci tsaro a can. Wannan ya haifar da littafin "Alarm i Atlantvallen" ("Alarm a cikin Atlantic Wall"). Littafin nan a Faransanci ya sa Janar Charles de Gaulle ya rubuta wasiƙa na godiya.