During the Korean War, Michaelis commanded the 27th Infantry Regiment (the "Wolfhounds") 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 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.