Don Front
The new field fortified regions were most extensively employed during Operation Ring. Don Front was outnumbered by the German forces of 4th Panzer and 6th Armies, but those armies were in no position to attack to break the siege due to lack of supplies. Don Front employed six field fortified regions, 54th, 115th, 156th, 77th, 118th, and 159th, to protect and cover wide swaths of the encirclement front, enabling the field armies of the Front to concentrate the bulk of their combat forces in narrow, carefully selected main attack sectors. This use of fortified regions in an economy of force role proved so successful that the Red Army routinely employed them in the same fashion, but on an even larger scale, for the remainder of the war.