Many military establishments, including NATO and Warsaw Pact forces, rely heavily on the mobilization of reservists to bring active duty up to strength and to man mobilized formations. Countries with highly controlled social structures and long and intensive training periods of military conscripts permit them to maintain a more significant pool of trained reserve manpower than is maintained by other countries. In cases where long distances or sea crossings have to be travelled make mobilization difficult. The rapid reinforcement of land force is a very complex operation that demands the timely availability of numerous resources, particularly transport aircraft and shipping as well as reception and prepositioned equipment storage facilities. Reinforcement of air forces involves infrastructure and logistic problems of a different but also complex nature, particularly in the areas of survivability and combat support. While a number of reinforcement air squadrons may be available to deploy to a combat zone, they would have to wait for the arrival of their ground crew and support equipment before they can become operational.