Monday 30 May 2016

Tanks at the Mannerheim Line

"Technical Meeting Minutes

Factory #185
May 9th, 1940
Chairman: comrade Barykov

Report by comrade Koloyev about the anti-tank defenses in the Summa region on the Karelian Isthmus.

The Mannerheim Line was built with the forces of four large capitalist nations. The Karelian Isthmus is bounded on two side by Lake Ladoga and the Bay of Finland, or to be more exact the Vyborg Bay. The isthmus, like all of Finland, is scarred by lakes, rivers, heights, and becomes one large foothold covered by a system of anti-tank fortifications. Let us examine one small region of the front line near Summa.

Summa is located 12 km from Boboshin and 20 km from Vyborg. Here is where the Mannerheim line begins. More then ten large one and two storey reinforced concrete bunkers can be found here over a mere 2-3 km of front line, well hidden and connected by underground tunnels, covered with trenches protected with metal shields, granite and reinforced concrete tank traps, ditches, minefields, barbed wire, and other obstacles. The latter extend from the bunkers and cross several times along the front.

The region is split up into sectors which are easily covered by fire from the bunkers, trenches, and other strongholds. The radial direction of the barbed wire is done to prevent rapid expansion from one penetration of the front. Figure #2 shows a sketch one bunker, to the left of the highway. It is difficult to find the bunker at a first glance, even though the sketch is not precise. We see a hill and nothing more. In reality, this is one enormous two storey concrete fortification. Figure #3 shows a photo this bunker from a distance, taken from the Vyborg highway (left side) and figure #4 is taken from close up. You can barely see small rocks 1.5-2 meters tall on the hill. These are firing ports. There is also a hidden armoured turret. A line of trenches is before the bunker, covered by 15 mm thick armoured shields. Each shield has three small slits that you can fire through. Trenches are protected by barbed wire, tank traps, an anti-tank trench, all of which are crossed by the radial extensions of barbed wire. Figure #5 shows a diagram of the top floor of the bunker from figure #4. The external walls are reinforced concrete, 1-1.5 meters thick. The reinforcing steel rebar is 10-30 mm thick.

Photo #6 shows the lower floor, deep underground. Here is where the maintenance and auxiliary rooms are: barracks, kitchens, ammunition and food warehouses, a well with water. Fresh air is delivered to the structure with a hand-cranked mechanism. The hand crank is considered more reliable, as an electric mechanism can be destroyed during combat. The lighting is electric.

Figure #7 shows a diagram of the armoured observation turret, which is built into the 1.5 meter thick ceiling. The turret extends 0.5 meters above the roof. There are 6 50 mm by 150 mm observation ports in it. A 20 mm thick armoured ring with two vision slits, one 3 mm by 150 mm, the other 15 mm by 150 mm rotates inside the turret on ball bearings. The observer, sitting on a special seat, has two vision slits in front of him, and rotates the ring with his elbows. He can observe by aligning the slits with one of the observation ports. The other ports are covered by the ring. The narrow 3 mm wide slit is used when the enemy is near or when there is danger of the slit being hit. The observer enters the turret via a ladder made from 35-40 mm thick steel pipes. Figure #8 shows the blown up turret and the thickness of the armour. Figure #9 shows remnants of the turret after the explosion. An enormous pressure built up inside the bunker when it was blown up, throwing chunks weighing tens of tons 30, 50, and even 100 meters. Sometimes, entire sections of the roof were blown away.

Figure #10 shows a firing port from the same bunker, a slit 20 mm by 740 mm. In case of danger, the crew can cover the slit with a sliding panel from the inside. Figure #11 shows the firing ports and vision slits. This is one type of bunker.

The second type has no lower floor and is significantly smaller (figs. 12, 13), and is typically located in depth of the defenses. After some experience, the Finns understood that the Red Army will penetrate the main line of defenses and hurriedly built new bunkers to deepen their defenses. Photo #13 shows an uncamouflaged part of a bunker and rebar, which indicates that the bunker was built hurriedly and not finished. Figure #25 shows the entrance to the bunker, the exit is in figure #36.

All approaches to the bunkers are carefully protected by all possible anti-tank obstacles: trenches, traps, wolf pits, walls, and other obstacles. Routes convenient for tanks are blocked by granite Dragon's Teeth and boulders (figs. 27, 28, 29). Figs. 32-41 show what remains after battle. Figure #41 shows a 12 meter wide and 6-7 meter deep crater formed by "Voroshilov's kilograms" [anti-tank grenades] by Heikkaniemi railroad station. Figure #42 shows a knocked out British Vickers tank. The rest of the report deals with fighting bunkers, tank traps, mines, trenches, etc. After the report ended, there were questions for the speaker. Let us focus on the questions dealing with tanks.

Q: What countries built the bunkers?
A: Britain, France, Germany, Sweden.

Q: What could tanks do if they could be shot through?
A: The bunkers were defeated by combined arms action from all types of forces, from tanks to aircraft, artillery, sappers, and infantry. A brief but powerful artillery barrage started the offensive. Then tanks and infantry attacked. Tanks and towed sleds brought in sappers, infantry, and explosives. Sappers blew up the bunkers, in some cases sealing or burying the firing ports. This is how the line was penetrated.

Q: What was the maximum gun caliber in the bunkers?
A: The main caliber was 37 mm with a muzzle velocity of 900 m/s, mostly Swedish. In addition, there were British and Italian guns. There were also some 45 mm guns, but few, most of them were at Vyborg.

Q: What are the most vulnerable parts of the tank?
A: All parts are vulnerable.

Q: Is there any point in armouring the suspension?
A: No point. You need to armour the ball bearings, there's no point in armouring anything else.

We were often cautious of wide tracks, thinking that they are easier to hit and disable the tank. In reality, it is harder to disable a wide track than a narrow track. It is enough to hit a narrow track with one shell or high caliber bullet to tear it, but one penetration of a wide track does not break the link. It is unlikely that two shells will hit in one place, I never saw it happen.

Q: Can we assume that there were civilian settlements in the fortified region?
A: The settlements were strongholds. Each house had guns, machineguns. The walls of the houses were no thinner than the walls of the bunkers. It's safe to assume that there were no civilians.

Q: Do you have any information about the units deployed by Finland?
A: No information, but it is known that the Finns had a powerful army numbering 500,000.

A series of other questions was asked.

The speaker was senior engineer from factory #185, Koloyev."

V. Lehn Collection


  1. ...I think comrade Koloyev may have been exposed to a little too much of that "Maginot of the North" bullshit the war correspondents liked to cook up...

  2. It is a shame there are no photos with the article. However, I own a copy of Bair Irincheev's book Talvisodan (Winter War: Forgotton Images) and I have walked the remaining fortifications near Summa. Impressive engineering, although the tank defenses were designed for much lighter T-26 tanks than anything heavier. Some of the "boulder" tank obstacles were ridiculously small when compared to the tanks that operated against them.