From the testing of chemical and biological weapons on soldiers and some civilians during the Cold War, to the vast use of toxic herbicides such as Agent Orange in Vietnam, to the unexplained illnesses suffered by veterans of the first war in Iraq, military service has sickened generation after generation of U.S. service members. But when confronted with ill and dying veterans, the nation's military leaders have turned to a time-honored tradition: denial. For years flames lapped at the sky, sending thick black plumes of smoke into the air across Iraq and Afghanistan. Yet even as the military's own environmental health experts quietly warned that the toxic fumes from open-air burn pits, located at every major U.S. base across the war zones, might sicken troops, military health officials stood their ground. The pits, they said, were not a danger. But veterans groups, families and members of Congress pressed for a more thorough investigation as thousands of warfighters returned suffering from respiratory illnesses, skin diseases, cancers and blood diseases.