On 2 September 1943, Welter was transferred to 5. "Staffel" (5th squadron) of "Jagdgeschwader" 301 (JG 301), a night fighter squadron that experimented with the use of largely radar-less single-seat Focke-Wulf Fw 190A-5 and Fw 190A-6 fighter aircraft by night, often equipped with the FuG 350 "Naxos" radar detector, used in the form of German night-fighter operations without AI radar — due to "Düppel" interference from RAF Bomber Command aircraft. These free ranging interception operations were called "Wilde Sau" (wild boar). On his first "Wilde Sau" intercept mission against Allied bombers on the night of 22 September 1943, Welter shot down two Allied four-engine bombers. He shot down a further two on his third mission on the night of 3 October 1943. By the beginning of April, he had accumulated 17 victories in only 15 missions. Subsequently, on 10 May 1944 Welter was awarded the German Cross in Gold. "Leutnant" Welter was transferred to 5. "Staffel"/Jagdgeschwader 300 (JG 300) on 7 July 1944.