Complex sentence: Lahm was promoted by President Franklin D. Roosevelt to honorary major general and served as commander of the Gulf Coast Air Corps Training Center at Randolph Field, Texas, from October 21,1941, to his mandatory retirement on November 20,1941.
Split into simpler sentences: Lahm was promoted by President Franklin D. Roosevelt to honorary major general. Lahm served as its commander from October 21,1941, to his mandatory retirement on November 20,1941.