Sieckenius was in command of 16th Panzer Division in Italy from May to November 1943, defending capably against the Allied landings at Salerno, and managing the subsequent withdrawal to the Viktor Line on the Volturno River north of Naples. At the beginning of October 1943 16th Panzer was already moving to the Adriatic coast sector as a result of Allied pressure when an amphibious landing was made at Termoli. Sieckenius' performance in that battle was the reason for his sacking as commander of 16th Panzer, as it was considered he had not been sufficiently aggressive in repelling the landing, and an opportunity to hand a defeat to the Allies had been lost, along with an important defensive position.