[Note 1] The Reservestaffel was a training squadron equipped with the Messerschmitt Bf 109 D-1, at the time based at Bad Aibling and subordinated to the I. Gruppe (1st group) of Jagdgeschwader 51 (JG 51—51st Fighter Wing).

On 26 August, during the German mobilization phase, the Reservestaffel was ordered to Fürstenfeldbruck where it was tasked with providing fighter protection over Munich.

[3] World War II in Europe had begun on Friday 1 September 1939 when German forces invaded Poland.

[2] He claimed his first victory on 14 May during the Battle of France when he shot down a Bristol Blenheim bomber 12 kilometres (7.5 miles) east of Sedan.

[5] On 23 July 1941, he claimed six Spitfires shot down in one day, an "ace-in-a-day" achievement, taking his total to 21 aerial victories.

He received the award from Feldmarschall (Field Marschal) Hugo Sperrle with fellow JG 2 "Richthofen" pilots Leutnant Egon Mayer and Oberleutnant Rudolf Pflanz on that day.

The triple award presentation was recorded by the Deutsche Wochenschau (German Weekly Review), a newsreel series released in the cinemas.

His 32nd claim was a Handley Page Halifax heavy bomber shot down on 30 December in the vicinity of Brest.

He was then shot down and wounded, bailing out of his Focke-Wulf Fw 190 A-2 (Werknummer 0326—factory number) 12 km (7.5 mi) southwest of Abbeville.

In fear of an Allied invasion on the French Mediterranean coast, I. Gruppe was ordered to Marseille-Marignane airfield on 8 November.

[17] That day, Leie's predecessor as Gruppenkommandeur, Oberleutnant Rudolf Busch, was killed in action when he collided in mid-air with Geschwaderkommodore Oberstleutnant (Lieutenant Colonel) Karl-Gottfried Nordmann.

[19] Flying from Oryol, Leie claimed a Mikoyan-Gurevich MiG-3 fighter shot down on 2 February, his first aerial victory on the Eastern Front.

The battle began on 5 July 1943 with I. Gruppe of JG 51 supporting the German 9th Army in its northern attack on the Kursk salient.

[21] On the first day of the Zitadelle, Leie claimed his 50th aerial victory, an Il-2 shot down in the vicinity of Maloarkhangelsk.

The offensive required the Luftwaffe to relocate its forces, defeated Army Group A, taking much of Poland and striking deep within the pre-war borders of Germany.

[29] As Geschwaderkommodore, Leie was ordered to Berlin on 22 January 1945 and attended the meeting with Reichsmarschall Hermann Göring which was later dubbed the Fighter Pilots' Mutiny.

The meeting was held at the Haus der Flieger in Berlin and was attended by a number of high-ranking fighter pilot leaders which included Leie, Günther Lützow, Hannes Trautloft, Hermann Graf, Gerhard Michalski, Helmut Bennemann, Kurt Bühligen and Herbert Ihlefeld, and their antagonist Göring supported by his staff Bernd von Brauchitsch and Karl Koller.

The fighter pilots, with Lützow taking the lead as spokesman, criticized Göring and made him personally responsible for the decisions taken which effectively had led to the lost air war over Europe.