Military career
During the early months of the First World War, he commanded Grenadierregiment "König Wilhelm I." (2. Westpreussisches) Nr. 7 in the field as its colonel. Future fighter ace Manfred von Richthofen witnessed the 22 August 1914, attack on Virton, Belgium, and wrote of Prinz Oskar's bravery and his inspirational leadership at the front of his regiment as they went into combat. For this action, Oskar earned the Iron Cross, Second Class. A month later, at Verdun, Oskar again led his men in a successful assault into heavy combat, and was awarded the Iron Cross, First Class. After this action, he also collapsed and had to be removed from the field. Awarded the wound badge for his injuries, he spent much of the autumn of 1914 recovering from what was reported to be a heart condition. He eventually returned to duty and served on the Eastern Front, where he was again awarded the wound badge.
In the early 1920s, his name was listed with other members of the general staff or the royal family accused of war crimes, and was condemned in the Press for applying for a colonel's pension from the Weimar Republic.
During the 1930s, when the Hohenzollern family attempted to test the waters for a return to power through Nationalist Socialism, Oskar appears to have played along, and eventually was commissioned at Generalmajor zur Verfügung (rank equivalent to brigadier general, "available for assignment"), circa 1 March 1940. As the family fell out of favour with Hitler (with the exception of Oskar's middle brother, August Wilhelm), it became evident that there would be no restoration of the monarchy through the Nazis.
With the early battlefield deaths of Oskar's son (also named Oskar, killed in Poland, September 1939) and his nephew (Wilhelm, son of the Crown Prince, died of wounds received in France, May 1940) the German people harboured a newfound sentiment for the royal family amidst the totalitarian regime that was Nazi Germany. As a consequence, the majority of royals serving in the German Armed Forces appear to have had their commissions canceled, including Prinz Oskar.
