Michaelis was a 1936 graduate of the United States Military Academy. In World War II, Michaelis was executive officer of the 502nd Parachute Infantry Regiment, but took command of the unit after the commanding officer, George Van Horn Moseley Jr., broke his leg in the drop into Normandy. Later, Michaelis was severely wounded in the Netherlands. He served as chief of staff of the 101st Airborne Division during the Battle of Bastogne and ended the war as a colonel. He served as aide-de-camp to General of the Army Dwight Eisenhower from 1947 to 1948. During the Korean War, Michaelis commanded the 27th Infantry Regiment at the Pusan perimeter, for which he received a Distinguished Service Cross. Early in the war, most American units were prone to breaking down and retreating. However his unit fared much better, General Matthew Ridgway believed, because of the fact that Colonel Michaelis had been an airborne commander and therefore did not panic whenever his unit was in danger of being surrounded. For as long as his unit preserved unit integrity with interlocking fields of fire, then it could handle being surrounded and cut off as they could be resupplied from the air. It was to become an important template used by Ridgway in his conduct of the Korean War once he assumed command from General of the Army Douglas MacArthur. Ridgeway's policy was to become one of "No more retreat" and he sought to acquire many more commanders like Michaelis as the war continued. In fact, shortly after Ridgeway took command, he began to improve the Army's morale by sending the units north, starting with Michaelis's unit, under an offensive named Operation Wolfhound in their honor. Michaelis's unit began a new phase of the war that started a complete turnaround for U.N. troops. He was promoted to brigadier general in 1951. Michaelis described the Turkish Brigade's combat readiness in unflattering terms, according to American historian Clay Blair. Blair wrote that war correspondents were misled into thinking that the Turks were "tough" fighters by their "flowing mustaches, swarthy complexions, and fierce demeanors", while in fact Blair declared them "ill trained, ill led, and green to combat." Blair quoted Michaelis as stating: In 1952, Michaelis returned to the United States and became commandant of cadets at the United States Military Academy. Later he commanded the Fifth Army. He was promoted to full general upon his retirement in 1972.
