After successful study colonel Engelhard was assigned as "Chief of the Reconnaissance Reconnaissance Department" of the "Ground Forces Command". On this position he served until 1987. In March, 1st 1988 he was designed to major general and became the "Deputy Chief of Staff for Operative", and little after "Deputy Commander in Chief and Chief of Staff in the Ground Forces Command". On September, 15th 1990 he was designed to the "Commander in Chief" of the National People's Army in the new East German "Ministry of Disarmament and Defense". With the disbandment of the National People's Army major general Engelhardt retired with effect of October, 2nd 1990. Upon the reunification of Germany on October 3, 1990, Engelhardt was selected to serve as a civilian advisor with the commanded by Lieutenant General Jörg Schönbohm. He was appointed advisor to the Bundeswehr liaison group headed by major general Hartmut Foertsch to the Group of Soviet Forces in Germany (Army General ; replaced by Colonel General on December 13, 1990). Additionally, Engelhardt was responsible for all general questions relating to the former National People's Army. Among numerous orders and decorations major general Lothar Engelhardt was awarded with: