[9] Schnell claimed his first aerial victory during the Battle of Britain on 29 July when he shot down a Bristol Blenheim bomber northwest of Le Havre.

[11] The focus of the airwar shifted in the next year to the Eastern Front, however Schnell stayed with JG 2 defending the West.

That day, Schnell claimed a Supermarine Spitfire fighter shot down east of Gravelines, his first aerial victory as Staffelkapitän.

[14][15] He continued to score consistently as the Royal Air Force (RAF) mounted heavier strikes into France, and temporarily held command of III.

Gruppe from 9 December 1941 to the following 28 January while Gruppenkommandeur (group commander) Hans "Assi" Hahn was on leave.

The objective of this operation was to give the German battleships Scharnhorst and Gneisenau and the heavy cruiser Prinz Eugen fighter protection in the breakout from Brest to Germany.

In support of this, the Luftwaffe, formulated an air superiority plan dubbed Operation Donnerkeil for the protection of the three German capital ships.

[19] After that his scoring rate slowed down as he focussed more on administration and command, and he led his unit in the changeover onto the new Focke-Wulf Fw 190—a very rugged dogfighter.

In a misguided idea by High Command to rotate the fighter Gruppen between Western and Eastern Fronts, III.

Gruppe of Jagdgeschwader 54 (JG 54—54th Fighter Wing) was transferred from the Eastern Front back to Germany for Defence of the Reich.

Hauptmann Schnell, was given command of the unit on 1 May 1943 to train and lead the pilots in high-altitude interception rather than the low-level brawling they were used to on the Eastern Front.

Gruppe defended against a raid flown by the United States Army Air Forces resulting in eleven Boeing B-17 Flying Fortress bombers shot down,[22] including three by Schnell.

[24][25] As mentioned above, command transfers between fronts were rare, given the markedly different combat conditions, and unfortunately Schnell was not lucky to be able to adapt quickly enough.

After less than a month and three further aerial victories,[26] he was shot down and killed in his Messerschmitt Bf 109 G-6 (Werknummer 411675—factory number) over the Russian offensive for Narva on 25 February 1944.

[24] According to Spick and Zabecki, Schnell was credited with 93 aerial victories claimed in an unknown number combat missions.