Czechoslovakian fortrification system - Heavy forts

Heavy forts - blockhouses

Heavy forts were built near the border with Germany and in some places in Slovakia near the border with Hungary. They were intended to stop enemy's main tank and infantry attacks. They were built in chains (space between forts is about 300-600 m). In some places artillery fortresses were built to provide the chain of independent forts with artillery support In Czechoslovakia there were built about 250 blockhouses between the years 1935 and 1938. Every fort was individually designed, so there are as many modifications as forts built, but we can divide them by their functions, shapes or by calasses of resistance. Shapes of early the types of the heavy forts were influenced by French types, but later there was a new type better suited for the Czech concept of defencence.

all numbers are in cm of reinforced concrete exept "bell / cupola" which is in cm of steel and "resistance up to caliber" Thickness of walls of heavy forts
resistance classceilingfront wallwall with main weaponsside of napebell / cupolaresistance up to caliber
1 12012080801515.5
215017580 or 100801518

Variations of types of heavy forts:

photo of infantry blockhouse MO-4
Infantry blockhouse MO-4 "U šedé vily" ("U sede vily")

Names of forts
Coordinating work on building huge numbers of heavy forts was quite dificult for ŘOP (ROP), so the line was divided to smaller independent sectors. Under these sectors were the fortification works command and also the building site guards. Initial letters of names of that sector was also given to name of fort, so every heavy fort has its uniqe number and usualy a name as well, e.g.N-S-85 "Montace", "N" means, that this fort is in sector Náchod (Nachod), "S" is for czech word "srub" - "blockhouse" in english - ("S" is not normaly written, most common is N-85 "Montace"), "Montace" is codename of fort.

Bells were cemented on the roof of forts. They were made of steel and were a place for observation, close defence of the fort and for signalling. Every bell was to be equipped with a periscope for observation. Bells have up to 6 embrasures for light MG vz.26 or MG vz.37. Bells were also used to control the fire of main weapons in bad weather conditions or in night. It was planned to use a 5 cm mortar in bells, but this weapon wasen't ready for use by 1938.
Another version of bells are observation bells, which were made especialy for observation for a fortress's artillery. They were made of the strongest steel and they have special additional internal armor to protect the observer from pieces of steel in case of hits. These bells should have had special periscopes, but they weren't mounted to the bells. They have one or three small openings for observations.

Sometimes the main weapons couldn't be used in embrasures "under concrete" (in normal embrasures on the upper floor), e.g. in hilly areas, so the mounting for weapon M (2x MG vz.37) or D (MG vz.37) was a special bell called a cupola. Cupolas weren't planned for observation or the defence of the fort like bells, but were planned for main fire upon enemy. Cupola is real consideration of weapon M or D "under concrete".

No turrets were mounted in forts, because only prototypes were under construction. There were three main types - artillery, mortar, and MG. All of them would have revolved 360 degrees and the artillery turret would also elevated up to a height of about 70 cm above the roof of the fort before firing and then retract after firing. The machinery that operated the turret would have been below the firing chamber. The turret would have been controlled either electrically or manually in case of emergency.
Artillery turrets (codename F3V or 2YRO) consisted of two parts - a fixed steel collar that surrounded the turret and provided further protection (175 - 450 mm thick) and a revolving steel dome (350 mm thick) that mounted two 10 cm howitzers and their gunners. Forts for these turrets were already built, but awaited their turrets. Forts for this turret are always part of fortresses, they weren't independent.
Mortar turrets (codename B12) also consisted of two parts like artillery turret, but this turret couldn't elevate. It would have been equipped with two 12 cm mortars. In 1938 there were only plans of this turret and weapon, so even forts for this turret were only in the planning stage. These forts were also always planned as part of fortresses.
MG turrets (codename OR) like the other turrets also consisted of two parts - one static and one revolving. This turret would have been used in forts that had a good field of fire towards the enemy. They would have been equipped with weapon M (2x MG vz.37). Forts for these turrets were already built, but in 1938 there was only one prototype of the turret. Forts intended for this turret are infantry blockhouses in resistance class III or infantry blockhouses of fortresses (all blockhouses of fortresses are resistance class IV).

Weapons used or planned for use in heavy forts
weaponcodenamecaliber (mm)range(m)rounds per minutecomments
light MG vz.26N 7.92200-1500600 vz. = Mk. (in English)
heavy MG vz.37D7.92300-2500550  
2x MG vz.37 M7.92300-2500 2x 550  
4 cm gun +
MG vz.37
max. 5800
-for 4 cm gun
-for MG
4 cm gun Q47max. 5800 35after cane of L1 production ended
10 cm howitzerY100max. 1195015-20 never entered production
5 cm mortarU50.9 60-80020never entered production
9 cm mortarG90300-440025-30never entered production
12 cm mortar 120250-750012never entered production

photo of weapon L1 - 4.7 cm gun with MG
Weapon L1 (4.7 cm gun with MG vz.37) in left
casemate of N-82 "Brezinka"
Main weapons of each infantry blockhouse were in embrasures "under concrete" (for flanking fire at enemy) or in steel cupolas (for direct fire at enemy). Weapons in casemates were L1, M, D, G (G only in lower floor). There were many combinations of weapons in each casemate and it depended on the location and tactical function of each blockhouse, but there were at least one embrasure for M and three embrasures at most - two in upper floor (eg. L1 and M or M and D) and one embrasure for G in lower floor. Each casemate of a blockhouse could have various combinations of weapons. Weapons in cupolas were M or D. Weapons (three Y) of artillery blockhouse were in one big casemate that comprised the whole upper floor. There is one exception, K-45 has two embrasures in upper floor and one in lower, because it was built on the side of a peak. Weapons for forts for artillery and mortar turrets were, of course, in turrets. Observation forts and entry blockhouses had no main weapons and used their weapons only for self-defence. Nearly every fort had some light MGs for close defence of embrasures and the entrance.

Infantry Blockhouses

They are the most common in comparison with the other heavy forts; in fact one can say that all independent forts are blockhouses for infantry (there are only few exceptions - observation forts). The most common one is double-sided, with two bells, L1 (4.7cm gun + MG vz.37) and M (2x MG vz.37) weapons in casemates on each side and it has two floors. Embrasures with main weapons (L1, M) was always protected by light MG vz.26. These MGs were also in bells. A deep ditch in front of the embrasures of the main weapons protected them against attacks of enemy soldiers and assured that debris from any shelling did not obstruct the field of fire. These ditches are 2.1 m (resistance classes 1 and 2) or 3.1 m (I to IV) deep.

Design of typical infantry blockhouse
Upper floor (so called battle floor) is on the picture bellow.

  • Plan of typical infantry blockhouse R-74 "Na holem" - upper floor
plan of typical infantry blockhouse - R-74

  1. embrasure for one 47mm gun with MG vz. 37 so called "L1" weapon
  2. embrasure for two MGs vz. 37
  3. embrasure for one MG vz. 26
  4. bell for observation and for close defence with three embrasures for one MG vz. 26
  5. machine gun ammunition storage
  6. telephonist's room
  7. commander's room
  8. stairs to lower floor
  9. water tank and machine gun ammunition
  10. room of artillery officer
  11. embrasure for defence of entrance
  12. ditch

he lower floor usually consisted of quarters for soldiers, diesel generator, gas protection system, storage for ammunition, petrol and food, ground telegraph and latrine. There are some modifications in each fort, e.g. some forts near rivers don't have a lower floor, so everything is situated on the upper floor and these forts are larger. Upper and lower floor are connected by stairs in Class I, II, III, and IV forts. Floors in Class 1 and 2 forts are connected by ladder.


plan of fortress Dobrosov Fortresses were built usually on dominant peaks or hills and the distance between two fortresses is about 10 km, or even closer in the most vulnerable areas. The range of the 10 cm howitzer was about 11 km, so neighbouring fortresses could get artillery support from the others. There were plans to build 13 fortresses but in 1938 only five were built completely (Smolkov, Hurka, Bouda, Adam, Hanicka) and four were in progress (Dobrosov, Skutina, Stachelberg, Sibenice - in order of progress). Fortress consist of serval infantry blockhouses, one entry blockhouse, at least one fort for artillery turret, usually one artillery casemate (max.2) and in some cases a fort with a mortar turret (max.2) was planned. All blockhouses which belong to the fortress are connected by underground corridors and built in the highest resistance class - IV. Underground are large munition stores, barracks, hospital, latrines, diesel generators, large gas protection system, kitchen, food storage, water tank, fortress HQ etc. Main corridors and corridors to artillery blockhouses had a small railroad. Other corridors had a normal road.
In 1938 the military value of fortresses was very low, because neither the artillery turrets nor the howitzers in artillery casemates were mounted. Lifts, generators and much other equipment also weren't installed.

On the picture is fortress Dobrosov:
Entry blockhouse (N-S-77a never built)
Artillery casemates (N-S-75 and N-S-76, only N-S-75 was built)
Infantry blockhouses (N-S-72 and N-S-73)
Fort for artillery turret (N-S-74 never built)
Fort for mortar turret (N-S-77 never built)


antitank obstacles
Obstacles (with rozsochac) in front of MO-S-19 "Alej"

Space between both light and heavy forts was filled with obstacles against infantry or antitank obstacles. Infantry obstacles were at least in two lines, but were in serveral lines in vulnerable locations. Anti-tank obstacles were always mixed with obstacles against infantry and they were mainly deployed between blockhouses. Only in some places were antitank obstacles built between light forts .
Infantry obstacles (light) - were made of barbed wire mounted to cemented steel poles (up to 115 cm) and they had up to six lines. They were used between light forts and with antitank obstacles.
Anti-tank obstacles (heavy) - There were serval types of them. They were used sometimes between light forts, but mainly between blockhouses. The most common was type "A" which was constructed (in order towards enemy) of one strand of barbed wire mounted to cemented steel poles, one line of cemented posts (130 cm), then line of normal pins and one line of a special steel obstacle called "rozsocháč - rozsochac" (this obstacle was designed by Czech engineers and was widely used in WW2 by germans and even now it is in use, e.g. by Austria, to quickly block important roads in case of enemy attack). Other types of anti-tank obstacels were another combinations of various lines (eg. 2 lines of posts with 2 lines of poles, 2 lines of posts with two lines of "rozsocháč" etc.) A special obstacle was an anti-tank ditch which was 2 m deep and about 5m wide. The side facing the enemy of ditch was made of reinforced concrete which was 20 to 40 cm thick. This obstacle was built mainly in front of casemates to secure good fields of fire which could be compromised by wrecks of destroyed enemy tanks.

Czechoslovakian forts after 1939

damaged bell
Bell damaged by geman tests

After Germany occupied the Czech republic (Slovakia became "independent"),the German army tested the resistance of the forts. Many blockhouses were damaged by firing trials. There had been tests on some blockhouse's bells of special weapons which were used in attack at Eben Emael. Some steel components were removed from blockhouses and they were used in the Atlantic Wall (weapon L1 and its embrasures). All light forts in the Protectorate of Bohemia-Moravia were destroyed by the Germans. Some blockhouses near Ostrava and Opava were used at the end of WW2 by German units against the approaching Red Army. In '50s the Czech company "n.p. Kovošrot" ripped out remaining steel bells, cupolas and embrasures. Only a few of undammaged blockhouses remain - mainly near civilian houses which could have been damaged by explosion.
All fortresses became military stores or bases (exept "Bouda"). Many blockhouses became storage place for waste. Nowdays there are a few museums, but majority of blockhouses and light forts are in very bad condition and sometimes it is quite difficult to find even a blockhouse in impenetrable woods.