The U.S. military, the nation's single largest energy consumer -- at more than 1 percent of the U.S. total -- has made great strides in recognizing and reducing its reliance on fossil fuels. But experts say it also still has a long way to go. In 2006 alone, the Pentagon bought 110 million barrels of oil and 3.8 billion kilowatts of electricity. To put that in perspective, it's about what the entire world uses each day. Experts say making strides will require changing the culture of an institution accustomed to having everything it needs to get its job done.