The airfield at Montdidier came under heavy fighter bomber attack on 11 June followed by another attack on 12 June resulting in significant damage to the airfield. On 12 June Weissenberger filed a claim for three aerial victories. Together with his wingman, Unteroffizier (Sergeant) Alfred Tichy, he took off at 06:00 and during the course of 12 minutes shot down three P-47s.
At 07:02 Weissenberger shot down his third P-47 of the day but his Bf 109 G-5 (Werknummer 110256—factory number) was hit in the engine forcing him to bail out near Saint André. The airfield in Montdidier was rendered unserviceable and I. Gruppe was forced to relocate. It was first moved to Péronne, then to Chauny, a makeshift airfield between Noyon and Tergnier.