The logistic effort in Iraq is quite large, and much of it has to do with getting material into Iraq, mostly from Kuwait. Every day, the U.S. Army runs about 170 supply convoys (containing, on average, a dozen vehicles each) to American bases in Iraq. Most of the material moved is liquid (nearly 10,000 tons of water a day, and over 2,800 tons of fuel). About half the American vehicle movements are for supply and maintenance, the rest are for combat operations. Most American troops never leave their bases, except to come to them when they enter Iraq, and when they leave to go home. In past wars, over 80 percent of casualties were suffered by combat troops. But in Iraq, combat support troops, particularly those on convoy duty, have reduced combat troops share of casualties closer to fifty percent.