In March and April 1943, General Josef Kammhuber ordered IV./NJG 5 to Rennes, France to protect the German U-boat bases.

On the night of 27/28 April, Wilhelm Johnen in a Messerschmitt Bf 110 G-4 performed an emergency landing at the Swiss airfield at Zürich-Dubendorf.

Johnen and his crew were interned, and the Luftwaffe employed extensive political manoeuvring to ensure the Bf 110, equipped with the still secret SN-2 radar, was kept from close Allied examination and returned intact.

Then deployed to Jesau near Königsberg in East Prussia, present day Yushny, Bagrationovsky District, night operations against Soviet bombers followed for the remainder of 1944.

Flying Junkers Ju 88 G-6 "C9+GA" (Werknummer 622 319—factory number) his air gunner parachuted to safety while his radio operator was also killed.