High quality reprint of this recently declassified 1969 study. Combine adverse effects of darkness and weather conditions on air operations in a combat situation, and a very hazardous operational environment is likely to prevail. This CHECO report investigates problems and limitations of the impact which darkness and weather have on air operations in Southeast Asia. Throughout this report, special emphasis is placed on tactics, techniques, and innovations developed to counteract unfavorable effects of night and weather on mission accomplishment.