Fortress Europe- European Fortifications Of World War II

by J E Kaufmann

  The exact number of bunkers and fortified positions the Finns built, remains a matter of speculation. Mannerheim's count of sixty-six strong points of two or more bunkers each does not agree with General H. Ohquist, his subordinate, who commanded the II Corps in the Karelian Isthmus. According to William Trotter (See A Frozen Hell), Ohquist's number was higher because he counted strong points that included mostly weak, older structures.

  The Western Section of the line consisted of mostly machine gun bunkers. The Eastern Section included about half a dozen artillery positions and about one fifth of the machine gun bunkers as in the other section. An important artillery strongpoint secured the right flank at Koivisto and another the flank of Lake Ladoga at Taipale.

  One of the most common positions was the korsut or wooden bunker that varied in size and shape, and was not able to withstand heavy artillery fire. The main works were concrete bunkers mounting machine guns. The newer ones could resist 152-mm weapons while the largest bunker housed a squad of men and held four machine guns. A few positions were designed for field guns up to 75-mm. Since most fighting was done in trenches outside the bunkers, the lack of heavy weapons positions did not matter much. The majority of the bunkers were vulnerable because their weapons fired forward, but there were some that used flanking fire.

  There were several types of bunkers, each designed to fit its location. Most bunkers had accommodations for the troops, but some only had a firing chamber. An unusual type of bunker, designed but not built, was to have been dug into the ground, its roof flush with the surface. It would have been outfitted with a small lift to carry a heavy machine gun to the firing position, its barrel pointing upwards. Once elevated, the weapon would fire across the roof of the bunker.

  At Muolaa at least one bunker mounted a 75-mm naval gun. Its 2.0 meter thick roof was able to withstand hits from weapons smaller than 200-mm. It consisted of a gun room, munitions storage, ready room, and protected entrance way, and measured about 7 meters on its longest sides. Another bunker at Vuoksen Lauttaniemen housed four field guns, two firing on either side. It included crew quarters and its maximum width was only about 6 meters.

  Between 1920 and 1924, 182 concrete positions were built in the Karelian Isthmus, 168 of which were erected in the main line, 144 in the vicinity of Taipale. The remaining fourteen positions occupied the Janis Line and a rearward position. Most of these positions were concrete machine gun bunkers.

  New types of bunkers were designed in the 1930s, 101 of which were built between 1936 and 1939. In addition, forty of the old bunkers were overhauled and eleven were modernized. In some cases, the exposed firing position of the older machine gun bunkers was concreted over and covered with earth. The bunkers were transformed into troop shelters. In some of the modernized bunkers underground facilities and/or additional chambers and protection were added. Among the newer constructions were more standardized machine gun bunkers, some with a cloche, an observation bunker with a cloche, shelters for an infantry squad with protected entrances, and a bunker for a battalion command post of about the same size as the troop shelter. The largest bunkers, mainly the shelters and command posts and a few types of machine gun bunkers, were usually no longer than about 10 meters.

  Two of the most famous bunkers near Summa, known as the Million Mark Bunker and the Poppius Bunker, were linked to two other bunkers by underground tunnels. The firing rooms of Poppius held a single machine gun. Million Mark Bunker, located not far from it, had two larger combat positions, one of which had two heavy and one light machine gun and a searchlight. The other position had one less heavy machine gun. It also had three cloches, one of which was in a central position on the tunnel, in an observation block. In both bunkers the accommodations for the garrison were located in the tunnel.

  In the fall of 1939, the Mannerheim Line consisted of twenty-nine sectors. Its bunkers were given an identification number consisting of a prefix derived from the abbreviation of the name of their sector, and a number designation. Each sector included fortified groups of one or more concrete bunkers or korsut, wire obstacles, and gun positions, and trenches. Of a total of 150 concrete machine gun bunkers, only 13 mounted two machine guns and 7 three machine guns. The remainder were single weapon bunkers. Slightly over 100 of these bunkers were built in the 1920s and only 7 were renovated in the 1930s. That means that slightly over 50 could be considered of sufficient strength to resist enemy fire. Only 8 gun bunkers and 9 command bunkers were built in the 1920s and none were added after that. Of a total of 41 troop shelters, only 12 were new and 3 were renovated bunkers.

  Trenches, obstacles and camouflage also played an important part in the Finnish defenses. Thus six concrete trenches no more than 100 meters long were built in the 1920s along with a large number of korsut and wood-lined trenches. In addi tion, stone obstacles in the form of boulders weighing up to 3,000 kg, were laid in two rows in an attempt to stop tanks. Barbed wire was nailed to trees and stakes driven into the ground. However, this type of obstacle was not covered by fire from the bunkers and was mostly intended to warn of an enemy approach. The Finns also took advantage of wooded areas with great skill. For instance, they built observation posts in the trees, either below tree top level or above. Wooden towers allowed a good view above the tree tops. They also expertly camouflaged the defensive positions.

  The Finns used no minefields in the Mannerheim Line even though they did manufacture their own anti-tank mines. The M-36 mine was similar to the German Teller mine and the M-39 mine was more cylindrical. In 1939, Finnish army depots produced 5,000 such mines. During the Winter War soldiers and depots produced 13,000 of the M/S-39, a wooden box mine with 8 kg of explosive, which was deployed as enemy vehicles approached, and was not placed permanently in any type of defensive mine field.

  The Finns also produced anti-personnel mines. Among these was an anti-personnel mine with 1 to 5 kg of explosive that could be ignited by pressure or trip wire. The troops in the field produced their own "tube mine" consisting of a can filled with explosive and detonated like regular land mines. Again, these were used as booby traps rather than in mine fields.

  Until 1941 only two types of cloche were used in Finland. One was small, with an inner radius of 40 cm. The other, was larger, with an inner radius of 55 cm, weighed 9 tons. It served as an observation cupola. Both cloche types were one-man positions with a maximum armor thickness of about 17 cm, able to resist shells from 8-inch guns. They had observation slits and an interior rotating ring with two slitsone for a submachine gun and the other for observation-that could be turned to any crenel or rotated so as to block all openings. These cloches were made at the Finnish Karhalan Konepaja or Karhala Machine Works.

  The Forward Position, located in front of the Mannerheim Line and adjacent to the Neutral Zone, was manned by the Border Guards and local troops. This position did not constitute a part of the Mannerheim Line, but served to delay the enemy in conjunction with the Demolitions Zone. Both the Neutral Zone and the Demolition Zone consisted mainly of field fortifications.

  The intermediate position and Back Line, on the other hand, had no permanent concrete structures. All their bunkers, built during the Winter War, were even smaller than the earlier works.

  2. The Salpa Line

  This new line included bunkers generally smaller and stronger than those of the Mannerheim Line. Most machine gun bunkers no longer fired forward, but to the flanks. They were also more skillfully adapted to the terrain than before, and many were built into the rock. Although the line was not completed, the number of works finished in the first construction phase (spring 1940 to summer 1941) and the second phase (June to October 1944) was substantial. The permanent structures included:

  This was a total of 802 positions including fire control bunkers and other types not listed. In addition to these positions the Salpa Line comprised about 350 km of trenches, 49 Russian tank turrets armed with machine guns, 1,250 covered machine gun positions, 720 troop shelters, 500 artillery positions, an
d 400 fire control (observation) positions. The line also contained boulders averaging 3,000 kg in weight, placed in four rows of 200 km instead of the more conventional concrete dragon's teeth. These stone obstacles were heavier than those used in two rows built during the Winter War.

  The machine gun bunkers varied in size. One of the larger types held twenty men and an observation cloche, and had machine gun embrasures covering the flank and the "L" shaped entrance. This type measured about 14 meters by 9 meters and had a concrete thickness of just under 2 meters. Initially, the machine guns were mounted on a makeshift wooden frame, but this was later replaced with a metal one.

  The anti-tank gun bunkers housed a 45-mm weapon and normally also included an observation cloche that was almost three times thicker than those used in the Mannerheim Line.

  The "Ball Bunker" was created by excavating a site and using a large rubber ball as a form for the concrete inner walls. When the concrete dried and the frame was removed, the roof of the shelter was spherical. It was then covered with earth and was accessed from a trench. This type of shelter held about ten men.

  Most of the bunkers in the Salpa Line had a higher resistance than those of the Mannerheim Line and their cloches were much stronger. These new bunkers were classified according to their ability to withstand bombs. Thus the first class or heaviest bunkers had a roof thick enough to withstand a 1,000 kg bomb.

  Normally, the men in the bunker communicated with those in the cloche through a voice tube. However, in the artillery control positions they used a telephone.

  In addition to the concrete bunkers, the Salpa Line contained a large number of korsu or wooden bunkers. About fifty turrets from captured Soviet tanks armed with machine guns were installed in 1943 and later.

  Like the Mannerheim Line, the Salpa Line also contained a variety of obstacles but no wood-lined anti-tank ditches. During 1943 the stone dragon's teeth were tested with captured Soviet tanks. An experimental section of concrete dragon's teeth was placed in the Karelian Isthmus in 1943. It consisted of four rows, each looking like a large concrete coffin with a ridge down the center and one end raised. However, these obstacles were not installed in the Salpa Line.

  Fields of anti-tank and anti-personnel mines were also to be included in the Salpa Line. The first mines were laid in the spring of 1941, but they were removed in the summer. In 1944 no mines were laid out because the engineer units in charge of their installation were at the front.

  After the Winter War, the majority of the new bunkers were outfitted with a steel sheet, steel netting or 2-inch wooden planks, to line their ceilings. A tube passing through the concrete next to the door carried a telephone line to the trenches. The walls and the ceilings of the machine gun firing rooms were lined with sound absorbing material. The machine gun crews were issued masks linked to hand operated fans to prevent suffocation. In 1943 the rear wall of the bunker was made thin enough to be easily broken from the inside and provide an escape route for the crew.

  The permanent bunkers were heated with wood-burning stoves that were also used for cooking. In addition, hand-cranked fans created a slight over-pressure in the event of a gas attack. The bunkers were linked to the outside by telephone or radios with their antennas placed inside concrete.

  3. Coast Defenses

  The army coastal defense force not only protected the coastline from invasion, but supported operations on the landward side. Several important coastal forts and batteries occupied key positions. Forts Makiluoto and Kuivasaari were the only two actually resembling forts.'

  In 1939 some of the key support positions for the Mannerheim Line and Finnish forces on the Karelian Isthmus were:

  Some of these coastal defenses, such as Fort Russaro, were located on islands. Others, such as Battery Tiurinsaari and three other batteries, were on the Karelian's west coast. Others still, such as Battery Konevitsa and three other batteries, guarded Lake Ladoga. Petsamo on the Arctic coast had a battery of two 87-mm guns, but these weapons were so old that they did not even have a recoil mechanism.

  During the Continuation War, new coastal defense positions were created, including twenty-five on Lake Ladoga that mounted weapons ranging from 75-mm to 152-mm guns. Additional coastal defense positions became operational by 1944. Their main weapons included 155-mm, 152-mm, 120-mm weapons, and a few larger guns.

  One interesting fact has recently come to light. The Finns had made arrangements with the Estonians so they could coordinate the actions of Fort Makiluoto with the batteries at Naissaari to effectively close the Gulf of Finland with artillery fire in 1939. When the Soviets forced Estonia into their camp, this effective barrier was eliminated.

  WEAPONS AND EQUIPMENT

  The Finns produced most of their own weapons, including foreign models of aircraft. The Tampella company at Tampere manufactured 40-mm Bofors anti-aircraft guns, the 37-mm anti-tank guns, and field guns. The Valmet Company built foreign aircraft under license. Most of the small arms, except pistols, were made in Finland. Finnish industry also produced such items as the cloches for bunkers and small warships. Some items such as tanks, naval mines, and aircraft had to be imported. Most of the heavy coastal guns were old Russian models.

  WORLD WAR II

  When the Winter War began in November 1939, the Finns quickly mobilized their few divisions and prepared to resist the Soviet invasion. The Army of Karelia, which comprised the majority of the army divisions, took up positions to defend the isthmus. Two of the coastal artillery regiments garrisoned the batteries of the Karelian isthmus: the 2nd Regiment on the west coast and the 3rd Regiment on the Lake Ladoga coast.

  Despite the fact that the Finns had only about one hundred 37-mm anti-tank guns and a similar number of 40-mm anti-aircraft guns, they managed to halt the Red Army, which was poorly prepared for this type of war. Further north, the Soviet divisions penetrated the "Wilderness" regions, only to be cut off, isolated, and destroyed later in January. Outnumbered and outgunned, the small garrison of Petsamo was forced to withdraw in the first days of the war.

  The Red Navy took part in the action early in the war when, on December 1, 1939, the heavy cruiser Kirov and two destroyers approached Fort Russaro. The Finnish artillery commenced firing at a range of 23 km, hitting one of the destroyers and forcing the Soviets to flee. On December 14, two destroyers and aircraft attacked Fort Uto, located off the southwest coast, but the fort's 152-mm guns sank one of the destroyers and drove off the other. The last Soviet naval offensive came on December 18, when the battleships October Revolution and its escort, subjected Fort Saarenpaa on Koivisto, the western flank of the Mannerheim Line, to heavy bombardment. At first the guns of the fort were unable to respond, and the warship began to inflict damage with its 12-inch guns. However, one of the fort's guns was finally returned to action and, after several near misses, forced the enemy to withdraw. The next day the battleship Marat and its escort started bombarding Saarenpaa, leveling many of the fort's surface structures. However, the Finnish gunners finally managed to score a critical hit on the battleship, forcing it to retire.

  The Finnish border units had withdrawn into the Mannerheim Line by December 6. During the following days, battle raged around the fortified positions at Taipale and Summa. The older bunkers from the 1920s generally collapsed under the weight of the Soviet artillery barrages, but the newer ones stood up reasonably well. However, since the Finns seldom fought from the bunkers, their destruction had little impact on the battle. Heavy fighting took place around the Summa area beginning on December 17. Two days later a Soviet force of 100 tanks lost 20 of its vehicles to the Finns so the battle was called off on the third. On December 25 the Soviets launched a second major attack on Taipale, but again were unable to achieve a major success.

  In January, the Soviet forces settled in to fight a trench war in the isthmus. The bunkers near Summa, particularly the Million Mark Bunker and the Poppius Bunker, resisted heroically, inflicting heavy casualties among the Soviets. As a result they became key obj
ectives for the Soviet offensive of February.

  In February and March the Finnish forces finally buckled under the Soviet steamroller. The stone dragon's teeth proved easy to drive over in the snow. In addition the coastal waters of the Gulf and Lake Ladoga had frozen, so that the Soviets were able to attack across the ice in an attempt to outflank the Mannerheim Line. However, the Finnish coastal batteries fired their large shells into the ice, literally breaking the ice under the Soviets' feet, inflicting heavy losses and, in one case, sinking tanks.

  Nonetheless, the Soviets continued their relentless advance, using heavy guns to destroy many of the remaining bunkers of the line. In those bunkers that withstood the bombardment, the crews died from the concussion.

  The Million Mark and Poppius bunkers, once more under attack, became the scene of heavy fighting and hand to hand combat. Mannerheim was forced to pull back to the intermediate line by the middle of February, and to the Back Line on February 27. The Finns sued for peace by the end of the month, but the Soviet troops continued to smash through the Back Line, near Viipuri early in March.

  The Finns, left with no more resources to continue the fight, could only stand by as the Russians tore up their front. The Finnish army took heavy casualties, losing about a third of its infantry. The Soviet guns of over 200-mm caliber proved to be the undoing of the fortifications of the Mannerheim Line.

  Now the victor, Stalin dictated the peace terms, taking what he had demanded before the war, but withholding compensation. Hanko and Fort Russaro became Soviet bases. Most of the Karelian Isthmus, including Viipuri, the second largest Finnish city, the Finnish Arctic coast, and Petsamo with its nickel mines, became Soviet territory.