Osterkamp was born in Aschersleben, modern day Saxony-Anhalt. When the First World War started he was studying forestry but decided to enlist in the German Army. He was rejected for service due to his "slight build" and he instead enlisted in the Marinefliegerkorps in August 1914. He then flew with the 2. Marine-Fliegerabteilung in Flanders. During 1915–1916, he served as an air observer, and became the first German pilot to fly a land-based aircraft to England on a reconnaissance-mission. Osterkamp claimed his first kill on 6 September 1916 as an observer to pilot Leutnant zur See Wilhelm Mattheus in a LVG C.II two-seater aircraft. In March 1917, he joined the Kampffliegerschule in Putzig and then joined Marine Feld Jagdstaffel 1 on the 14th of April 1917 On 21 March 1917, Leutnant Osterkamp took command of Marine Feld Jagdstaffel 2 He scored a total of 32 victories during the war, and was awarded the Prussian military orderPour le Mérite on 2 September 1918, and was one of the last individuals to receive it. .
Interwar years
Osterkamp joined the new Luftwaffe on August 1, 1933 with the rank of Hauptmann. He also participated in the second, third and fourth FAI International Tourist Plane Contest Challenge 1930, Challenge 1932 and Challenge 1934. By the time the war broke out in September 1939 he was a Oberstleutnant in command of the Jagdfliegerschule 1.
World War II
On 19 September 1939, Oberst Osterkamp was appointed Geschwaderkommodore of Jagdgeschwader 51. During the Battle of France, he claimed four victories. During the Kanalkampf period of the Battle of Britain in July 1940, he claimed a further two victories, bringing his total to six. He was replaced as commander of JG 51 by Werner Mölders on 23 July with the latter formally taking command on the 27th of July. Promoted to Generalmajor, Osterkamp was awarded his Knight's Cross of the Iron Cross on 22 August 1940. Following his replacement in JG 51, Osterkamp was appointed Jagdfliegerführer 2, the commander of fighter aircraft in Luftflotte 2. On 1 August 1942, he was transferred to Luftgaustab z.b.V. Afrika. On 5 April 1943, he was appointed Jagdfliegerführer Sizilien and served until replaced on 15 June by Adolf Galland. He then served in a number of staff positions until being appointed Inspekteur der Luftwaffen-Bodenorganisation in 1944. After criticism from High Command, he was dismissed from the service on 21 December 1944.
Post-war career
In 1960, he was appointed honorary chairman of the Gemeinschaft der Jagdflieger, the Association of Fighter Pilots.
