A fortified district or fortified region (Russian: Укреплённый район, Укрепрайон, ukreplyonny raion, ukrepraion) in the military terminology of the Soviet Union, is a territory within which a complex system of defense fortifications was engineered. ^{[1][2][3][4][5][6]}

Each fortified district consisted of a large number of concrete bunkers (pillboxes) armed with machineguns, antitank guns and artillery. The bunkers were built in groups for mutual support, each group forming a centre of resistance. The area in between was filled with various barriers and obstacles, as well as mine fields. A dedicated military unit (Fortified district troops) was permanently assigned to man each region.

The concept of ukrepraions was developed during the Russian Civil War, when large territories were to be defended by relatively sparse military force. The first military units named so appeared in 1923.^[2]

In 1928 the program for the construction of the comprehensive system of fortified districts was launched. It started with 13 fortified districts, which over time evolved into the Stalin Line.^[2]

Beginning in early 1942, long after the fortified lines in the west had fallen, the Red Army began organizing a somewhat different sort of unit, also known as a "Field" Fortified Region (District). These were brigade-sized in terms of manpower (apx. 4,500 men), with anywhere between four and eight machine gun - artillery battalions, a signal company, a medium mortar company, and other supporting units. They were not tied to any fortified line and had some, mostly horse-drawn, mobility, so are sometimes referred to as "field" units, as opposed to the pre-war units, which were static.

"Strong in artillery and machine guns and weak in riflemen, the fortified region was used as an economy of force minor formation for purely defensive tasks such as the holding of passive sectors or the flank of a penetration."^[7]

In effect, as Soviet production of heavy weapons vastly increased in the middle part of the war, while manpower was hard put to keep pace, the men of the fortified regions were almost entirely trained as heavy weapon crews, in order to hold ground by firepower rather than by manpower. This was a very practical solution, given that so much of the Soviet-German front was impracticable for offensive action by either side.

The new field fortified regions were most extensively employed during Operation Koltso. 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.^[8]

Of the 47 fortified regions in the Red Army at the end of World War II, more than 30 were used to form machine gun artillery brigades and the rest were disbanded. By the 1950s the fortified regions in the Far East had been disbanded, and only a few remained in the Transcaucasus and Karelia, using different TO&Es from the World War II units (see http://www.ww2.dk/new/army/other/ur.htm). As Sino-Soviet tensions increased during the 1960s, the Soviet Army began to create new fortified regions to provide security in the Far East.^[9]

The first two, the 97th and 114th, were formed in March 1966 to protect the Transbaikal railways. Each included three motor rifle battalions with four companies each, four tank battalions with four companies equipped with T-34-85, IS-2, IS-3, IS-4, T-54/T-55, and OT-55 tanks. The units also included a separate machine gun artillery battalion of six companies, two of which were equipped with ten OT-55 and IS-4, and separate sapper, communications, repair and recovery battalions, as well as an anti-tank battalion with 18 85 mm guns and a rocket artillery battery with 4 BM-13 Katyusha units.^[9]

By the late 1980s, ten fortified regions were located in the Primorsky and Amur regions, five in the Transbaikal, one in Kazakhstan, and four on the Turkish border. The organization of each fortified region differed according to the needs of their respective military districts. However, each fortified region generally included between three and five separate machine gun artillery battalions (with some additionally including a motor rifle battalion), a tank battalion and between one and three battalions or companies of tank turrets dug in as pillboxes, one to three artillery battalions or separate batteries (including rocket and anti-tank), an anti-aircraft rocket battalion or battery, a separate communications battalion or company, an engineer-sapper battalion, company, or platoon, and support and maintenance units.^[9]

The machine gun artillery battalions of the fortified regions differed little in their organization, usually consisting of two machine gun companies, a motor rifle company, and a mortar battery. Depending on their location, they could also consist of a company of tank turrets dug in as pillboxes, two or three artillery caponiers, and a ZPU-2 anti-aircraft gun platoon. Machine gun companies consisted of three platoons each armed with six PK and PKS 12.7 mm machine guns, the 12.7 mm NSV heavy machine gun, the AGS-17 automatic grenade launcher, and the SPG-9 anti-tank grenade launcher.^[9]

The motor rifle units of the fortified regions had a similar structure to other motor rifle units and were mostly equipped with ZIL-131 and GAZ-66 trucks. The tank battalions numbered 31 tanks, generally T-54s or T-55s and sometimes including OT-55 flamethrower tanks. Separate rocket battalions were equipped with 18 BM-21 Grad or BM-13 systems, six per battery; anti-tank batteries were equipped with six 100 mm MT-12 anti-tank guns. During the fall and winter of 1989, during the reorganization of the Soviet Army, most of the fortified regions were reorganized into machine gun artillery regiments of newly created machine gun artillery divisions.^[9]