Kammala wannan jumla: Stjernfelt ya kammala karatu daga Royal Swedish Naval Academy a 1940 kuma an ba shi izini a matsayin jami'in kuma an ba shi izini ga Vaxholm Coastal Artillery Regiment a ranar 9 ga Afrilu, a baya da aka tsara 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 babban sha'awar tarihin soja. Ba da daɗewa ba bayan ƙarshen Yaƙin Duniya na II, ya hau keke tare da sabon matarsa Borghild tare da bakin tekun mamayewa na Normandy, suna 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.