Complex sentence: It is the leading science and technology laboratory of the Department of Defense for the development, testing, and evaluation of medical chemical warfare countermeasures including therapies and materials to treat casualties of chemical warfare agents.
Split into simpler sentences: It is the leading science and technology laboratory of the Department of Defense for the development, testing, and evaluation of medical chemical warfare countermeasures. These countermeasures being therapies and materials to treat casualties of chemical warfare agents.