Sapper army A Sapper Army ( ) was a multi - brigade military construction engineer formation organized by the Soviet Union ' s Red Army during World War II . Formed to construct large - scale defensive works , Sapper armies were used from late 1941 until mid - 1942 when the Red Army opted to organize smaller and more flexible construction engineer formations . Although the organization of military construction engineers into an army - level echelon was unusual , the use of dedicated troops for military construction was common to many armies of World War II . History . Reeling from the German invasion of 1941 , the Soviets decided to organize large military construction engineer formations to construct defensive works on a massive scale . The Soviets hoped such works would strengthen Red Army defensive operations and buy enough time to rebuild their forces for a counter - offensive . Consequently , the high command ordered the formation of the first sapper armies on October 13 , 1941 . Originally , six sapper armies were formed , but by December 1941 this was expanded to ten sapper armies , numbered First through Tenth . The sapper armies were not only composed of military personnel ; " women , old men , schoolchildren and teenagers under the draft age " were also mobilized to serve in the construction units . The sapper armies worked to construct defensive lines that were made up of battalion and company strong points in the Moscow , Stalingrad , North Caucasus , and Volga military districts . Sapper armies also trained troops for the Red Army ' s engineers and consequently suffered a steady loss of qualified personnel . Dissatisfied with the relative lack of flexibility of the sapper armies , the high command disbanded five of them in February 1942 and used the released personnel for the formation of new rifle ( infantry ) units . Confronted with the German summer offensive of 1942 , the remaining sapper armies built defensive works around Moscow and Stalingrad , and in the Caucasus . On July 26 , 1942 , the high command directed the reorganization of the sapper armies , and by October 1942 , the remaining five sapper armies had been converted into defensive construction directorates . The troops released by this measure were used to form new rifle and smaller engineer units . Historian David Glantz assessed the effectiveness of the sapper armies as having " . . . contributed significantly to the Red Army ' s victories at Leningrad , Moscow , and Stalingrad by preparing defensive lines , providing vital engineering support to the Red Army ' s operating fronts , and serving as a base for the formation of other more specialized engineer forces assigned to operating fronts . " Organization . Sapper armies were made up of two to four sapper brigades . A sapper brigade controlled 19 sapper battalions , each with three companies of four platoons . Sapper battalions had an authorized strength of 497 men , and included woodcutting units , road - and bridge - building units , units dedicated to the construction of defensive positions , and motorized tractor units . Fully manned , each sapper army was authorized some 45 , 000 to 50 , 000 men . Sources . < br >