The investigation into the accidental bombing of Canadian troops in Afghanistan last month has brought up again the fact that combat pilots operating on a busy schedule are authorized to use amphetamines to keep them awake and alert, as well as sedatives so they can get to sleep when their mission is over. Air force regulations call for 12 hours of rest between missions, but this is not always possible in combat. During the 1991 Gulf War, about two thirds of the combat pilots were using the air force prescribed drugs. Transport pilots on long transoceanic flights were also authorized to use the drugs. Commercial airline pilots are not allowed to use the drugs. Many airline pilots in air force reserve units were called up for the Gulf and Afghanistan wars and many of these pilots are against the use of the drugs (fearing that some pilots may get addicted.) The use of such stimulants in combat first became common during World War II.