From the start of the war until December 1940, Trettner served as Staff Officer, Operations (Ia) in the Staff of the 7th Paratroop Division until 14 June 1939. He was later appointed Chief Of Operations in the Staff of the XI. Paratroop Corps (15 December 1940 to 6 April 1942), taking part in the airborne operation on Crete. He was promoted to Chief of Staff of the XI. Paratroop Corps, but on 4 October 1943 was reassigned to head formation and become Commanding Officer of the 4th Parachute Division, a command he held until 3 May 1945, when he surrendered to US troops.
Cold War
Trettner was released from internment in April 1948 and worked initially for the charity Caritas. In 1949, he enrolled at the University of Bonn and studied Economics and Jurisprudence, and received his diploma in Economics in 1956. Trettner then joined the Bundeswehr and was transferred to the Supreme Headquarters Allied Powers EuropeSHAPE in Paris serving as commander of the logistics department until 15 September 1959.
Trettner's 1964 appointment as Inspector General incurred criticism from the East German DDR government. Senior Communist official Albert Norden alleged that Trettner had been involved in the bombing of Guernica, during the Spanish Civil War.[2] In 1965, former Spanish Republican Air Force commander Ignacio Hidalgo de Cisneros made a public statement criticizing Trettner's Bundeswehr appointment.[3] As Inspector General he apparently had a poor relationship with Karl Gumbel, the civilian Deputy Minister of Defence, and objected to taking orders from a civil servant, Gumbel, in the absence of the Minister. He was also opposed to a ruling by the Minister, in the face of a court order, that members of the military could join a union. These factors led to his resignation, which nearly coincided with that of Werner Panitzki, the chief of staff of the Air Force.[4]
Trettner was one of the umpires for the 1974 Sandhurst wargame on Operation Sea Lion. Heinrich Trettner was Catholic, and in 1978 he published an article, The Holy See and disarmament, in the German-language edition of the Vatican literary journal Communio, and a corresponding reply the next year.[5]
Trettner died one day before his 99th birthday. He was the last living general of the Wehrmacht.
Fellgiebel, Walther-Peer (2000) [1986]. Die Träger des Ritterkreuzes des Eisernen Kreuzes 1939–1945 — Die Inhaber der höchsten Auszeichnung des Zweiten Weltkrieges aller Wehrmachtteile [The Bearers of the Knight's Cross of the Iron Cross 1939–1945 — The Owners of the Highest Award of the Second World War of all Wehrmacht Branches] (in German). Friedberg, Germany: Podzun-Pallas. ISBN978-3-7909-0284-6.
Scherzer, Veit (2007). Die Ritterkreuzträger 1939–1945 Die Inhaber des Ritterkreuzes des Eisernen Kreuzes 1939 von Heer, Luftwaffe, Kriegsmarine, Waffen-SS, Volkssturm sowie mit Deutschland verbündeter Streitkräfte nach den Unterlagen des Bundesarchives [The Knight's Cross Bearers 1939–1945 The Holders of the Knight's Cross of the Iron Cross 1939 by Army, Air Force, Navy, Waffen-SS, Volkssturm and Allied Forces with Germany According to the Documents of the Federal Archives] (in German). Jena, Germany: Scherzers Militaer-Verlag. ISBN978-3-938845-17-2.
Thomas, Franz; Wegmann, Günter (1986). Die Ritterkreuzträger der Deutschen Wehrmacht 1939–1945 Teil II: Fallschirmjäger [The Knight's Cross Bearers of the German Wehrmacht 1939–1945 Part II: Paratroopers] (in German). Osnabrück, Germany: Biblio-Verlag. ISBN978-3-7648-1461-8.
Thomas, Franz (1998). Die Eichenlaubträger 1939–1945 Band 2: L–Z [The Oak Leaves Bearers 1939–1945 Volume 2: L–Z] (in German). Osnabrück, Germany: Biblio-Verlag. ISBN978-3-7648-2300-9.