[1] Dahl was born on 27 March 1916 in Lug near Bad Bergzabern, son of a Volksschule teacher who was killed in action in 1918 on the Western Front of World War I.

[2] In May 1941 Dahl was posted to Jagdgeschwader 3 (JG 3—3rd Fighter Wing) and claimed his first victory on 22 June during the first day of the invasion of the Soviet Union.

[4] On 21 May 1944, Dahl was appointed commander of Jagdgeschwader zur besonderen Verwendung (JG z.b.V.—a special purpose fighter wing).

He led the unit until taking command of Jagdgeschwader 300 (JG 300—300th Fighter Wing) on 27 June 1944.

Dahl set up his Geschwaderstab (headquarters unit) at Ansbach, planning combined operations with JG 3 "Udet".

A series of accidents at the start of the mission allowed the Luftwaffe to focus their attacks on the B-24 force.

(Sturm) Gruppe Jagdgeschwader 3 escorted by two Gruppen of Bf 109s from JG 300 led by Dahl.

Dahl drove the attack to point-blank range behind the Liberators of the 492nd Bomb Group before opening fire.

[9] The majority to the Sturmgruppe attack, IV./JG 3 lost nine fighters shot down and three more suffered damage and made crash landings; five of the unit's pilots were killed.

[13] On 26 January 1945, Hermann Göring appointed him Inspekteur der Tagjäger (Inspector of the Day Fighters).

[15] Following the war, Dahl became a member of the Deutsche Reichspartei (DRP—German Reich Party)[17] In the West German federal election of 1961 he unsuccessfully ran as a candidate for the DRP.

[19] Among others, the founding meeting was attended by Adolf von Thadden and Erich Kern, the honorary president was Hans-Ulrich Rudel.

Dahl was a spokesman for the German People's Union, a nationalist political party founded by Frey.