One unspoken reason for not invading Iraq during the Spring or Summer of 2002 is the heat. No, not just the obvious impact of 100 degree (F) heat on the troops, but the even greater impact of that heat on gas turbine engines (as used in M-1 tanks and helicopters.) That level of heat reduces the horsepower of those engines by close to 50 percent. Pilots and tank drivers will try to compensate by pushing the engines even harder, which results in more engine failure and more maintenance to keep the equipment going. Many vehicles are air conditioned, and this equipment gets stressed as well. You usually can't turn off the AC, mainly because it's there to cool equipment, not troops. All of this is not theoretical. When American troops began to arrive in Saudi Arabia in the Summer of 1990, they ran head first into these problems. Training in that heat was hard enough, but no one wanted to fight in it.