The majority of his victories were claimed over the Western Front in Defence of the Reich missions against the Royal Air Force's Bomber Command.

In February 1943, Drewes was appointed Staffelkapitän (squadron leader) and transferred to Nachtjagdgeschwader 1 (NJG 1—1st Night Fighter Wing) in August 1943.

Drewes was born on 20 October 1918 in Lobmachtersen, at the time in the district of Wolfenbüttel, present day a borough of Salzgitter, Lower Saxony.

[1] Drewes passed his Abitur (School Leaving Certificate) at the Reformrealgymnasium in Wolfenbüttel and joined the military service in the Army on 2 November 1937 as a Fahnenjunker.

He initially served with Panzer-Regiment 6, a regiment of the 3rd Panzer Division, in Neuruppin and was posted to the Kriegsschule in Munich, Bavaria on 15 November 1938 as a Fähnrich.

[2] He was trained as a pilot,[Note 1] receiving his A/B-licenses in April 1940 at the Luftkriegsschule 3 (LKS 3—3rd air war school), Wildpark-West near Werder.

On 1 May, his flight training progressed at the Flugzeugführerschule (C)5 where he received his C-Certificate on 30 August followed by attending the Blindflugschule 3 (3rd Blind Flying School) at Königsberg, East Prussia.

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

Gruppe (2nd group) and was equipped with the Messerschmitt Bf 110 twin-engine heavy fighter, flying combat air patrols over the North Sea and German Bight.

Gruppe of ZG 76, also known as the "Shark Group" (Haifischgruppe) due to their distinct coloring scheme, was then transferred to Greece during the Balkans campaign.

There, German forces under the cover name Special Staff F supported the Iraqi rebels during the Anglo-Iraqi War in their attempt to gain independence from the British Empire.

[7] Drewes, and two other pilots, was then flown to Rhodes, Greece on an Italian Savoia-Marchetti SM.79 medium bomber, tasked with bringing new aircraft to Iraq.

The return flight never made it past Aleppo where the task force was ordered to retreat to Athens and then to Leeuwarden, the Netherlands.

[10] Following the 1939 aerial Battle of the Heligoland Bight, RAF attacks shifted to the cover of darkness, initiating the Defence of the Reich campaign.

Each sector named a Himmelbett (canopy bed) would direct the night fighter into visual range with target bombers.

Drewes claimed his first aerial victory as a night fighter pilot on the evening of 17 January 1943 when he shot down a Short Stirling bomber.

[10] He claimed his second nocturnal aerial victory on over a Handley Page Halifax bomber in the vicinity of Store Heddinge on 14 March 1943.

[15] His adjutant in the group at the time was Oberleutnant Walter Scheel, who later became the President of West Germany (1 July 1974 – 30 June 1979).

[17] There he built a career as an entrepreneur and married Dulce Hurpia, a Brazilian woman, who gave him a son, Klaus Drewes, a lawyer in Brazil.

[21] This and the ♠ (Ace of spades) indicates those aerial victories which made Drewes an "ace-in-a-day", a term which designates a fighter pilot who has shot down five or more airplanes in a single day.