On 22 June 1941, the first day of Operation Barbarossa, Schellmann was posted as missing in action, presumed killed.

Schellmann was born on 2 March 1911 in Kassel, at the time in the Prussian province of Hesse-Nassau in the German Empire.

[4] This squadron was subordinated to I. Gruppe (1st group) of JG 135 under the command of Major Max Ibel and was based at Bad Aibling.

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

[9] In October 1939, Schellmann was summoned by Generalleutnant Hubert Weise, at the time commanding general of Luftgau III in Berlin, to the Reichsluftfahrtministerium (RLM—Ministry of Aviation).

[11] Based on the order issued on 11 October, Schellmann was appointed Gruppenkommandeur (group commander) of II.

[15][Note 1] On 17 May, the Gruppe moved to Attenrode and Schellmann claimed a Westland Lysander aircraft shot down southeast of Brussels.

[15] On 3 June, Schellmann and his Gruppe moved to an airfield named Mannessecourt and participated in Operation Paula, the failed attempt to destroy the remaining units of the Armée de l'Air (ALA—French Air Force).

[14] That day, Schellmann claimed his last aerial victory of the campaign when he shot down an ALA Morane-Saulnier M.S.406 fighter near Compiègne.

Gruppe was ordered to Beaumont-le-Roger, patrolling the English Channel and participated in the occupation of Guernsey on 1 July.

[20] Schellmann claimed his first aerial victory during the Battle of Britain on 18 July when he shot down a Bristol Blenheim bomber north of Le Havre.

[22] In late August it was becoming apparent to the Oberkommando der Wehrmacht (German High Command) that the Battle of Britain was not going as planned.

The frustrated Commander-in-Chief of the Luftwaffe, Hermann Göring, relieved several Geschwaderkommodore of their commands, and appointed younger, more aggressive men in their place.

[23] In consequence, on 2 September, Schellmann was given command of JG 2 thus succeeding Oberstleutnant Harry von Bülow-Bothkamp who was transferred.

[26] Schellmann claimed his only aerial victory as Geschwaderkommodore of JG 2 on 26 September 1940 when he shot down a Spitfire fighter near the Isle of Wight.

[24] He replaced Major Bernhard Woldenga who had temporarily assumed command after Oberstleutnant Ibel had been transferred on 10 October.

[28][29][30] At the time of his transfer to JG 27, the Geschwader was based at Guînes at the English Channel and was subordinated to the II.

[33] On 30 April, JG 27 was then ordered to Eleusis where the Geschwaderstab was given a brief period of rest before being relocated to Suwałki on 4 June in preparation of Operation Barbarossa, the German invasion of the Soviet Union.

[39] According to US historian David T. Zabecki, Schellmann was credited with 25 aerial victories, 12 of which during the Spanish Civil War.