Once more, the U.S. Department of Defense has found that it cannot predict, with perfect accuracy, the type and quantity of supplies necessary for the next war. This was made most obvious when the pre-positioned stockpiles of equipment and supplies were used during the 1991 and 2003 operations in the Persian Gulf. Critics contend that the Department of Defense has to show more diligence in this matter. The critics appear to be unaware to just how much effort actually goes into trying to figure out this puzzle. And a puzzle it is, with thousands of different items in the pre-positioned stocks. The most critical factor is not so much the items themselves, but how many of the expendable ones you need. That means how many batteries, spare parts, rounds of ammo and so on. What makes this a very difficult (if not impossible) calculation to make is that the expenditure rates of most of these items is not just dependent on what your troops do, but on what the enemy does. It's kind of impossible, by definition, to get it exactly right, or even close. The stock levels are based on wargaming out "most likely scenarios." Experience has shown that if you stand ready to rush, by air or sea, needed items, you are better prepared than spending a lot of effort trying to predict the unpredictable ahead of time.