Complex sentence: Lehmann-Willenbrock was relieved in March 1942 by "Oberleutnant zur See" Hans-Jürgen Hellriegel, who was relieved in turn in March 1943 by "Oblt.z.S." Wilhelm Peters.
Split into simpler sentences: Lehmann-Willenbrock was relieved in March 1942 by "Oberleutnant zur See" Hans-Jürgen Hellriegel. He was relieved in turn in March 1943 by "Oblt.z.S." Wilhelm Peters.