Rosenstein volunteered for military service, joining the
Imperial German Army's 95th Infantry Regiment. He quickly transferred to the
Die Fliegertruppen, and was forwarded to aviation training at
Gotha on 24 August 1914. While training at
Fliegerersatz-Abteilung (Replacement Detachment) 5, he was promoted twice; the latter promotion, to
Vizefeldwebel came on 24 November 1914. From there, he was posted to
Flieger-Abteilung (Flier Detachment) 19 on 6 March 1915. On 29 March, he was awarded the
Iron Cross Second Class. His native
Kingdom of Württemberg awarded him its Silver Military Service Medal on 21 August 1915. On 17 February 1916, Rosenstein was
commissioned as a
Leutnant. On 28 April 1916, he was
wounded in action over the
Battle of Verdun. He was then awarded the Iron Cross First Class, having flown 180 combat
sorties to date. Upon recovery, he reported to
3rd Army as a Fokker pilot. He became one of the founding members of one of Germany's brand-new
fighter squadrons,
Jagdstaffel 9, founded 23 September 1916. He moved on to
Jagdstaffel 27 on 15 February 1917. While there, he frequently flew
wingman to
Hermann Göring. However, it would not be until 21 September that he scored his first aerial victory, when he shot down an
Airco DH.4 over
Zonnebeke while on a morning patrol. Five days later, his victim was a
Sopwith Camel. Then, in an unusual twist, he was sent for
aerial observer's training. On 8 January 1918, he was posted to
Kampfeinsitzerstaffel (Combat Single-seater Squadron) 1a. He was passed on to serve in
Kampfeinsitzerstaffel (Combat Single-seater Squadron) 1b on 4 April 1918. Flying with them, he scored his third aerial victory on 26 June, when he downed another DH.4. On 2 July 1918, he received his final war posting, to
Jagdstaffel 40. He promptly shot down a
Royal Aircraft Factory SE.5a on 14 July. On 28 September, he received his native kingdom's award of the Knight's Cross 2nd Class with Swords of the
Order of the Zahringer Lion. The following day, he began a run of five victories that took him through 27 October 1918. At about this time, Rosenstein was nominated for the
House Order of Hohenzollern. The war ended without Rosenstein scoring a ninth victory or receiving the Hohenzollern. ==Later life==