He was advanced to the rank of General on November 1, 2005 and began his assignment as the 30th Assistant Commandant of the Marine Corps on November 8, 2005. On July 2, 2008, he was succeed as Assistant Commandant by General James F. Amos. Magnus retired from active service in a ceremony on July 17, 2008 after 38 years of total service. Magnus received the Navy Distinguished Service Medal for his years of superior service to the U.S. military. He officially retired on September 1, 2008; at the time of his retirement, he was the last active officer of the Corps who had served in the Vietnam War.