On 18 November 1943 Harris began his Berlin offensive. "Oberleutnant" Johnen achieved two victories on the night of the 3 January 1944—matching his most successful night thus far—when he accounted for two Lancasters at 02:56 03:21; both fell southwest of Berlin. On 6 January Johnen claimed a Lancaster near Tutos at 03:27. A solitary claim against a Lancaster on 20 January north northwest of Berlin at 19:36 followed. Johnen filed three claims on the 27 January 1944. A trio of Lancasters were claimed between 20:36 and 21:18 southeast and southwest of Berlin. He achieved this success again on 15 February 1944. At 20:34 southeast of Damgarten Johnen claimed a Lancaster. Another over Kummenerer See at 20:45 and at 21:20 north northwest of Berlin for his 18th victory. Johnen was appointed to the position (not rank) of "Staffelkapitän" (squadron leader) on 29 March 1944.