Following the 1939 aerial Battle of the Heligoland Bight, Royal Air Force attacks shifted to the cover of darkness, initiating the Defence of the Reich campaign. By mid-1940, GeneralmajorJosef Kammhuber had established a night air defense system dubbed the Kammhuber Line. It consisted of a series of control sectors equipped with radars and searchlights and an associated night fighter. Each sector named a Himmelbett would direct the night fighter into visual range with target bombers. In 1941, the Luftwaffe started equipping night fighters with airborne radar such as the Lichtenstein radar. This airborne radar did not come into general use until early 1942. Semrau joined the long distance night fighter service flying intruder missions as a former destroyer pilot of Kampfgeschwader 30 in July 1940. In July 1940, elements of KG 30 were trained and converted to flying night fighter missions. These elements then the II. Gruppe of the newly created Nachtjagdgeschwader 1. On 11 September, II. Gruppe of NJG 1 was reassigned and became the I. Gruppe of Nachtjagdgeschwader 2 Kammhuber had created I./NJG 2 with the idea of utilizing the Junkers Ju 88 C-2 and Dornier Do 17 Z as an offensive weapon, flying long range intruder missions into British airspace, attacking RAF airfields. Until October 1941, I. Gruppe operated from the Gilze-Rijen Air Base. He claimed his first two aerial victories on the night of 10/11 February 1941 over two Bristol Blenheim bombers shot down near Feltwell. The Blenheim bombers belonged to No. 21 Squadron, the second of which was destroyed during the laning approach, killing all but the gunner. He took command of the 3. Staffel of NJG 2 in the fall of 1940. He fought in the Battle of Britain and in the Siege of Malta. Hauptmann Semrau received the Knight's Cross of the Iron Cross after 160 missions on 7 October 1942. Promoted to Major, he took command of the 4th Gruppe of Nachtjagdgeschwader 6 in June 1943. After two months he was transferred again, taking command of the 3rd Gruppe of NJG 2.
Wing commander and death
On 1 November 1944, Semrau was appointed Geschwaderkommodore of NJG 2. He was shot down on 8 February 1945 and killed in action on factory flight with his crew, Oberfeldwebel Hantusch and Fahnenjunker-Oberfeldwebel Behrens, of Junkers Ju 88 G-6 when he was intercepted during the landing approach at Fliegerhorst Twente by F/Lt K.S. Sleep of No. 402 Squadron RCAF on 8 February 1945. The aircraft of Semrau came down between Fliegerhorst Twente and Oldenzaal. He was posthumously awarded the Knight's Cross of the Iron Cross with Oak Leaves on 17 April 1945. He was the 841st member of the German armed forces to be so honored.
Summary of career
Aerial victory claims
Foreman, Parry and Matthews, authors of Luftwaffe Night Fighter Claims 1939 – 1945, researched the German Federal Archives and found records for 40 nocturnal victory claims. Matthews and Foreman also published Luftwaffe Aces — Biographies and Victory Claims, listing Semrau with 39 claims. Two claims dated 28/29 January 1944 and 30/31 January 1944 respectively are not recorded in Luftwaffe Aces — Biographies and Victory Claims while one claim dated on 2 November 1944 is missing in Luftwaffe Night Fighter Claims 1939 – 1945. Victory claims were logged to a map-reference, for example "PQ 05 Ost AD". The Luftwaffe grid map covered all of Europe, western Russia and North Africa and was composed of rectangles measuring 15 minutes of latitude by 30 minutes of longitude, an area of about. These sectors were then subdivided into 36 smaller units to give a location area 3 × 4 km in size.
