Following the 1939 aerial Battle of the Heligoland Bight, Royal Air Force (RAF) attacks shifted to the cover of darkness, initiating the Defence of the Reich campaign.
By mid-1940, Generalmajor (Brigadier General) Josef 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 (canopy bed) 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 (Fernnachtjagd) flying intruder missions as a former destroyer pilot (Zerstörer) of Kampfgeschwader 30 (KG 30—30th Bomber Wing) in July 1940.
In July 1940, elements of (Z)KG 30 were trained and converted to flying night fighter missions.
These elements then the II.
Gruppe (2nd group) of the newly created Nachtjagdgeschwader 1 (NJG 1—1st Night Fighter Wing).
On 11 September, II.
Gruppe of NJG 1 was reassigned and became the I. Gruppe of Nachtjagdgeschwader 2 (NJG 2—2nd Night Fighter Wing) 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 (Ritterkreuz des Eisernen Kreuzes) after 160 missions on 7 October 1942.
Promoted to Major, he took command of the 4th Gruppe of Nachtjagdgeschwader 6 (NJG 6—6th Night Fighter Wing) in June 1943.
After two months he was transferred again, taking command of the 3rd Gruppe of NJG 2.
Following the 1939 aerial Battle of the Heligoland Bight, Royal Air Force (RAF) attacks shifted to the cover of darkness, initiating the Defence of the Reich campaign. By mid-1940, Generalmajor (Brigadier General) Josef 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 (canopy bed) 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 (Fernnachtjagd) flying intruder missions as a former destroyer pilot (Zerstörer) of Kampfgeschwader 30 (KG 30—30th Bomber Wing) in July 1940. In July 1940, elements of (Z)KG 30 were trained and converted to flying night fighter missions. These elements then the II. Gruppe (2nd group) of the newly created Nachtjagdgeschwader 1 (NJG 1—1st Night Fighter Wing). On 11 September, II. Gruppe of NJG 1 was reassigned and became the I. Gruppe of Nachtjagdgeschwader 2 (NJG 2—2nd Night Fighter Wing) 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 (Ritterkreuz des Eisernen Kreuzes) after 160 missions on 7 October 1942. Promoted to Major, he took command of the 4th Gruppe of Nachtjagdgeschwader 6 (NJG 6—6th Night Fighter Wing) in June 1943. After two months he was transferred again, taking command of the 3rd Gruppe of NJG 2.
Paul Semrau