Complex sentence: On 1 December 1930 Reibnitz joined the Nazi Party, becoming member number 412855, and on 15 April 1933 he also became a member of the Cavalry SS, with the SS number 66010.
Split into simpler sentences: On 1 December 1930 Reibnitz joined the Nazi Party, becoming member number 412855. On 15 April 1933 he then became a member of the Cavalry SS, with the SS number 66010.