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Steve Anderson, a retired brigadier general who was Petraeus' chief logistician in Iraq, says that the Pentagon spends $20 billion a year just to air condition tents and temporary buildings in Iraq and Afghanistan. That's more than NASA's entire annual budget.

There's an easy fix, says Anderson: Spray tents with polyurethane foam. An existing $95 million contract to spray-insulate tents is providing $1 billion in cost-avoidance, Anderson says. But insulating tents instead of air conditioning them is still not official military policy.