The Soviet defence industry is one of the largest in the world; according to American estimates, it is the largest of all. The Soviet Union has given high priority to the creation of military power, has established special mechanisms for extracting resources from the society and channelling them into the defence industry, and has tried to shield defence production from the shortcomings of the rest of the economy. The Soviet Union invested heavily in the defence industry, and large proportions of the output of other sectors went to meet the needs of defence. The defence sector is drawing resources from an economy that has been profoundly conditioned by the requirements of Soviet security. The development of advanced military technology requires a large research and development effort. Foreign sales now absorb a substantial part of the output of the Soviet defence industry.