World War II in Europe began on Friday 1 September 1939 when German forces
invaded Poland. Herrmann flew 18 combat missions on the He 111 over Poland, including missions against Polish forces fighting in the
Battle of Kutno, and received the
Iron Cross 2nd Class () in October. On 31 May 1940 during the
Battle of Dunkirk, he was shot down by
Royal Air Force (RAF) fighters, resulting in a
crash landing of his
Junkers Ju 88 A-1 on the German held beaches near
Dunkirk. On 20 June 1940, he was appointed
Staffelkapitän (squadron leader) of 7.
Staffel of KG 4 and took part in the
Battle of Britain. He sank 70,000 tons of Allied shipping as a bomber pilot, and was instrumental in the attack upon
Convoy PQ 17. In February 1941 his group was transferred to
Sicily, from where it attacked
Malta then fought in the
Battle of Greece. In one attack Herrmann sank the ammunition ship in the
Port of Piraeus. The explosion sank 11 ships and made the Greek port unusable for many months. In July 1942 he was assigned to the general staff in Germany, where he became a confidant of Luftwaffe commander
Hermann Göring. In 1942 Herrmann was appointed to the
Oberkommando der Luftwaffe (OKL—High Command of the Air Force) staff.
The night air war 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. However, the
Himmelbett system had its deficiencies, a dense "
bomber stream", crossing the Luftwaffe aerial defenses in narrow area would saturate the
Himmelbett boxes. On the night of 30/31 May 1942, RAF
Bomber Command for the first time had used the "bomber stream" tactic in
Operation Millennium, the thousand-bomber raid on
Cologne. Herrmann, who red Kammhuber's reports, became increasingly concerned with the lack of preparation of OKL. He realized that the Luftwaffe would have to fight under conditions of numerical inferiority. Additionally, Herrmann knew that the
Himmelbett was costly and susceptible to counter measures. Although not a new idea, he proposed to operate single-seat day fighters in addition to the
night fighter force. In November 1942, Herrmann presented his ideas at a meeting of the night fighter staff. Initially, his views were rejected. By March 1943, Herrmann had managed to secure a
Focke-Wulf Fw 190 fighter at Berlin-
Staaken airfield and flew several training missions in
mock combat against a
Heinkel He 111 bomber. Encouraged by his experiments, Herrmann approached
Generaloberst Hubert Weise, the commander of
Luftwaffen-Befehlshaber Mitte (Luftwaffe Commander Central), asking support for a real intercept mission. Specifically, he asked if the
anti-aircraft artillery could be restricted to firing to a height of . Weise rejected the ask but had no objections if Herrmann was willing to risk flying into a barrage of shell bursts. In April, Herrmann put his ideas to the test when
Himmelbett detection reported a
De Havilland Mosquito bomber heading for Berlin. He managed to intercept the illuminated Mosquito near
Brandenburg an der Havel but failed to shoot it down. On 22 April, Herrmann was authorized to setup the
Nachtjagdversuchskommando (NJVK—Night Fighter Test Detachment) at Brandenburg-
Briest which became operational in early May. On 4 May, NJVK was equipped with fourteen aircraft at Brandenburg-Briest, twelve Fw 190As and two
Messerschmitt Bf 109G fighters, and two further Fw 190A fighters based at Staaken. He played a role in the creation of
night fighter wing
Jagdgeschwader 300 Wilde Sau (Wild Boar) using day fighters at night in response to the night raids of RAF
Bomber Command on Germany in mid-1943. As a single seat night fighter he scored 9 victories. On 5 September, Herrmann was injured in a flight accident when his
Fieseler Fi 156 Storch C-3 (
Werknummer 1297—factory number) suffered engine failure during takeoff at
Hennef. On 12 October, Herrmann was again injured when technical malfunction of his
Messerschmitt Me 210 A-1 (
Werknummer 6019) forced him to make a
gear-up landing at
Le Bourget Airfield. In December 1943, Herrmann was appointed Inspector of Night Fighters. By 1944 he was Inspector General of night fighters and received the Knight's Cross with Oak Leaves and Swords. At the end of 1944 he led the
9th Air Division. Herrmann was a leading exponent of the tactical deployment of
Rammjäger Sonderkommando Elbe (ram fighters), sent into action in April 1945. Suicide pilot volunteers, often aged 18 to 20, were to be trained only to be competent enough to control specially lightened and unarmoured
Bf 109 fighters and bring down Allied bombers by ramming the tail or control surfaces with the propellers of their aircraft and bailing out if possible. Herrmann's intention was to gather a large number of these fighters for a one-off attack on the
USAAF bomber formations in the hope of causing enough losses to curtail the bombing offensive for a few months. Fuel shortages prevented employment of the large numbers necessary, although from one mission of this type, on 7 April 1945, of the 120 fighters thus committed only 15 returned. On 11 May 1945, Herrmann was captured by Soviet forces and held
prisoner of war for 10 years and returned to Germany in October 1955. ==Law career and Nazi activism==