William ya yi yaƙi da Napoleon na I na Faransa a lokacin ɓangaren Napoleonic Wars da aka sani a Jamus a matsayin Befreiungskriege ("Yaƙe-yaƙe na 'Yanci", wanda aka fi sani da War of the Sixth Coalition), kuma an bayar da rahoton cewa ya kasance jarumi ne mai jaruntaka. An sanya shi kyaftin (Hauptmann) kuma ya lashe Iron Cross don ayyukansa a Bar-sur-Aube. Yaƙin da ya yi da Faransa ya bar tasiri a kansa, kuma yana da tsananin ƙiyayya ga Faransanci.A 1815, William ya ci gaba da zama babban kwamandan kuma ya umurci wani battalion na 1. Garderegiment. Ya yi yaƙi a karkashin Gebhard von Blücherett a yakin Ligny da Ligloo.
Oktoba 1849