The Department of Defense relies on hundreds, if not thousands, of weapons and products such as uniforms, batteries, and microelectronics that contain PFAS, a family of chemicals linked to serious health conditions. Now, as regulators propose restrictions on their use or manufacturing, Pentagon officials have told Congress that eliminating the chemicals would undermine military readiness. PFAS, known as "forever chemicals" because they don't break down in the environment and can build up in the human body, have been associated with such health problems as cancer. In July, a new federal study showed a direct link between testicular cancer and PFOS, a PFAS chemical that has been found in the blood of thousands of military personnel. In a report delivered to Congress in August, Defense Department officials pushed back against health concerns raised by environmental groups and regulators. According to the report, most major weapons systems, their components, microelectronic chips, lithium-ion batteries, and other products contain PFAS chemicals. These include helicopters, airplanes, submarines, missiles, torpedoes, tanks, and assault vehicles; munitions; semiconductors and microelectronics; and metalworking, cooling, and fire suppression systems. Beyond cancer, some types of PFAS have been linked to low birth weight, developmental delays in children, thyroid dysfunction, and reduced response to immunizations.