The advent of terrorist threats has heightened local, regional, and national governments' interest in emergency response and disaster preparedness. The threat of natural disasters also challenges emergency responders to act swiftly and in a coordinated fashion. When a disaster occurs, an ad hoc coalition of pre-planned groups usually forms to respond to the incident. History has shown that these "system of systems" do not interoperate very well. Communications between fire, police and rescue components either do not work or are inefficient. Recent disasters, such as Hurricane Katrina and the tsunami in Indonesia, have illuminated the weaknesses in emergency response. This paper discusses the need for defining requirements for components of ad hoc coalitions which are formed to respond to disasters.