The article is devoted to the issues of mobilization of the USSR economy during the Second World War. The author proposes a new method for determining the GDP of the USSR in 1940–1945 based on archival materials and achievements of modern historical and economic analysis of the national economy of the USSR during the Second World War. The author also considers a theory of economic mobilization during the Second World war of Alan Milward, applying his ideas to the analysis of the Soviet military economy. The author believes that the estimates of the GDP of the USSR adopted by A. Meddison and M. Harrison for the period of the Second World war are overstated. In this regard, the author concludes, based on calculations, that the growth of the Soviet economy in 1943–1945 was not as significant as is commonly believed, and the Soviet economy did not reach the pre-war level of GDP in 1945. In this regard, the author proves that the reserves of the Soviet economy before the Second World War were very limited, which is also explained by the limited relocation of resources between the agricultural and urban economies of the USSR. The survival of the Soviet economy during the Second World War was mainly due to the relocation of capital investments to the Central and Eastern regions of the country due to the occupation of less economically efficient western regions. In this regard, the author also hypothesizes that industrial clusters arose in the Central and Eastern regions of the USSR as a result of an evacuation.