Flying with this wing, Seifert claimed his first aerial victory on 10 May 1940 on the Western Front during the Battle of France fighter aircraft.

He was killed in action in mid-air collision with a Lockheed P-38 Lightning on 25 November 1943 near Béthune, France.

Jagdgeschwader 26 "Schlageter" (JG 26—26th Fighter Wing) was created on 1 May 1939 in Düsseldorf by renaming Jagdgeschwader 132 (JG 132—132nd Fighter Wing) and was commanded by Oberst Eduard Ritter von Schleich, a flying ace of World War I.

[2][Note 1] While Mathews and Foreman claim that Seifert first served in another unit flying the Messerschmitt Bf 110 heavy fighter during the Invasion of Poland before transferring to JG 26.

[5] World War II in Europe began on Friday 1 September 1939 when German forces invaded Poland.

This squadron was subordinated to I. Gruppe (1st group) under the command of Major Gotthard Handrick.

The claim was made over a Royal Netherlands Air Force Fokker D.XXI fighter shot down near Rotterdam.

[10] On 10 July 1941, the Gruppenkommandeur (group commander) of I. Gruppe, Hauptmann Rolf Pingel, was shot down over England and became a prisoner of war.

Gruppe of Lehrgeschwader 2 (LG 2—2nd Demonstration Wing) flew a fighter bomber attack on London.

[12] In 1941 Fighter Command began the Circus offensive over Belgium and France, beginning on 10 January.

485 (NZ) Squadron lost one Spitfire each, one pilot killed, the other captured, badly wounded.

54 and 55 on 21 July, claiming a 15 Squadron Blenheim that had lost an engine to ground-fire and accounted for a Spitfire in the afternoon to inflate his tally to 15.

[16] Pilot Officer Johnnie Johnson, future Wing Leader, remarked that the "Circus" was "badly bounced [jumped]" and his formation did not see the enemy until they had opened fire.

95, on the morning of 17 September, cost Fighter Command six killed, two captured and three wounded and nine Spitfires.

Authors Prien, Stemmer, Rodeike and Bock consider this claim unconfirmed, creating a one aerial victory discrepancy between the two sources as of this date.

Twelve Douglas A-20 Havoc bombers supported by the North Weald Wing had already bombed the airfield before they were intercepted over the Somme Estuary.

Leading I. Gruppe, Seifert encountered the attack force west of Somme Estuary and shot down a No.

[32] On 31 January, I. Gruppe moved to Riga and two days later to an airfield named Rielbitzi at Lake Ilmen.

[33] Seifert claimed his first aerial victory on the Eastern Front during the Battle of Demyansk on 16 February when he shot down an Ilyushin Il-2 ground-attack aircraft.

[34] On 23 February, Soviet forces attempted to cross Lake Ilmen by boat which were attacked by Fw 190s of the Stabsschwarm (headquarters flight).

[35] Five days later, he claimed two aerial victories, shooting down a Bell P-39 Airacobra and Lavochkin-Gorbunov-Gudkov LaGG-3, two fighter aircraft.

[38] On 14 March, I. Gruppe moved to an airfield at Dno, southwest of Rielbitzi and west of Staraya Russa.

The next day, he claimed his 53rd and last aerial victory on the Eastern Front when he shot down a Mikoyan-Gurevich MiG-3 fighter aircraft.

[41] On 20 May 1943, Seifert had to leave his command of I. Gruppe when transferred to a staff position with the Luftwaffe detachment of the Reichsluftfahrtministerium (RLM—Ministry of Aviation) in Bulgaria.

Unknown to Seifert, his mother had invoked the 'last surviving son' ruling as his younger brother, Gerhard, had been killed in action, and was thus allowed to be removed from active combat duties.

In consequence, his tour with the RLM ended and he returned to France in September 1943 and was appointed Gruppenkommandeur II.

[48] Four days later, during the second Schweinfurt raid, Seifert shot down a B-17 bomber from the 305th Bombardment Group, which lost 13 of its 16 aircraft, near Maastricht.

During combat, Seifert's Fw 190 A-6 (Werknummer 470006—factory number) collided with a P-38, and crashed near La Couture, 5 km (3.1 mi) south of Estaires, killing both pilots.

[50] The American pilot, Lieutenant Manuel Aldecoa bailed out but his parachute had failed to deploy properly and he fell to his death.

The Luftwaffe grid map (Jägermeldenetz) 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 360 square miles (930 km2).