The impact of an artillery shell on various types of shelters is an extremely interesting question. We have already touched it once (see Betonka of the First World War), and now we want to delve into the topic by looking at how the shells of especially heavy calibers (420-mm, 380-mm and 305-mm, called "suitcases" during the First World War)) could overcome various types of obstacles - in this case, the fortress of Verdun. The main source of the article was the little-known work of an outstanding Russian specialist on the topic - the colonel of the Russian army and the Red Army diviner V. I. Rdultovsky.
The Verdun Fortress vaults are classified into 3 main types:
No. 1 - Stone shelters made of sandstone or limestone, generally soft, with a thickness of 1 - 1.5 meters in the castle, covered with a layer of 2 - 5 meters of earth.
# 2 - Shelters made of the same materials, reinforced with a concrete mattress about 2.5 meters thick (sometimes less), with an intermediate layer of sand 1 meter thick.
No. 3 - Shelters with retaining walls made of special concrete, with ceilings made of reinforced concrete slabs of different thickness, depending on the position of the object at the front.
All of them are built on clay soil or on fissured limestone, more or less durable.
420 mm projectile
The total weight of the projectile is 930 kg, the explosive charge is 106 kg (a new projectile weighing 795 kg with an explosive charge of 137 kg was subsequently introduced). The shells had a tube with a deceleration, produced funnels from 8 to 13 meters in diameter and from 2.5 to 6 meters deep (depending on the soil). In clayey limestones, a 420-mm projectile sometimes cut a very deep channel. On February 18, 1915, one of these shells, which fell at an angle of 60 degrees to the horizon on the glacis of the fort, made a channel from 0.6 to 0.8 meters in a limestone rock with a rocky embankment (however, fractured and of rather poor quality) in diameter and 10, 1 meters along the trajectory, or 8, 75 meters, counting vertically.
Falling behind the escarp and counter-escarp walls, 420-mm shells destroyed them 8-15 meters in length - depending on the distance of the point of impact from the inner surface of the wall and on the properties of the soil and masonry.
4 of these bombs, falling on the fort behind the escarp and counter-escarp walls, created a gap in them about 30 meters long.
Type 1 stone buildings were pierced by these shells; the vaults were pierced like a knife, and the effects of gases often destroyed the facade walls of the casemates. In the slope of the earthen embankment, the projectile pierced a cylindrical channel 8 meters long, then successively pierced 2 vaults of 2 and 1.5 meters thick, and, finally, the top of the projectile dug 0.5 meters into the cellar wall.
Having got into the vault of unreinforced concrete 4 meters thick, a 420-mm projectile pierced it, and continuing on its way, broke through a wall 1 meter thick, and then penetrated the opposite wall by 0.5 meters; there was no explosion.
Although these projectiles undergo significant resistance when passing through embankments and masonry, the loss from this of their speed was not always sufficient for the action of the bottom tube with which they were equipped; that is why many of these shells did not explode. These shells could also penetrate the second vault.
Stone buildings of type No. 2 could have been pierced by these shells - as was the case on one of the forts on February 15, 1915: the vestibule at the bakery was pierced by one shell, and the vault of the bakery itself - by two shells that fell almost simultaneously. The hole formed was 3 to 4 meters in diameter. However, it should be noted that these vaults were protected by a 1 meter sanding powder over a concrete mattress only 1.5 meters thick.
One shell that fell over the entrance to a reinforced-type powder magazine destroyed the concrete 7 meters long, 3 meters wide and about 0.6 meters deep.
Type 3 shelters were often destroyed by these shells.
Reinforced concrete slabs 1, 25 meters thick, overlapping the communication passages, were pierced.
Reinforced concrete slabs 1.5 meters thick, covering shelters under the rampart, trunks and cellars, were also pierced, and slabs 0.25 meters thick, sometimes separating floors in shelters, were destroyed, probably by the action of gases, since there was only a small number of shell fragments were found. The bomb exploded in the slab; in fact, on the upper side of the slab there was a funnel about 0.7 meters in diameter and 0.6-0.7 meters deep; then followed by an explosion chamber, the concrete in which was turned into dust, and the iron was destroyed over a distance of 1.5 - 1.8 meters. In slabs 1, 5 meters thick, the last iron rods, before being broken, were strongly bent.
In one fort, a 1.64 meter thick slab covering the cellar was not completely destroyed; the last iron rods were not broken, and only bent, and the greatest bend of the latter reached 0.5 meters in circumference, 2, 2 - 2.5 meters in diameter. And the concrete, broken into pieces of medium size, still supported these rods. There were no traces of a shell explosion inside the room.
In one of the fortifications, a 420-mm projectile hit a slab 1.75 meters thick, overlapping the intermediate caponier, near its support, which caused only an insignificant deflection on its lower surface; the last rows of reinforcement remained unharmed.
Falling into concrete collars or foreshortenings of armored towers, 420-mm shells caused cracks in the massif, carrying it to a depth of 1 - 1.65 meters. At the same time, some of the shaped stones moved apart and collided with the place. The repair of such damage, in general, was carried out quickly.
These initial observations made it possible to state that slabs or masses of reinforced concrete, in order to withstand a single hit of a 420-mm projectile, had to have a thickness of at least 1.75 meters.
In one of the forts, the iron reinforcement of concrete was often exposed. There were no traces of the concrete mass into which she was immersed. Apparently, the separation of the iron reinforcement from the concrete mass was facilitated by the fact that the vibrations caused by the powerful impact and subsequent explosion of the projectile have different velocities and stresses in the iron and in the concrete, and thus contribute to the separation of these two materials.
In general, separation of successive concrete layers was noted around the impact sites of these shells, which was revealed by the delamination of the outer surface. Destroyed reinforced concrete was broken into small pieces and often turned into powder.
The 420-mm shell could destroy retaining walls, vaults and slabs of special concrete; he most often divided them into large chunks, about 0.5 cubic meters. meters. Some of them were thrown back by the explosion of the projectile, but others often remained in balance, thus protecting the array from complete destruction.
380 mm shells
Full weight 750 kg, explosive charge 68 kg, initial speed 940 meters per second.
In the embankments, these shells created craters 3 - 11, 5 meters in diameter and depth (in clay) from 4 to 5 meters. In sandy and stony soil, the depth was less.
The 380-mm projectile is equipped with a bottom tube without deceleration, and therefore explodes at the moment of impact on a solid barrier. If the structure did not have a slab, which took over the explosion of the projectile, then the projectile could destroy type 1 shelters, forming holes in them from 3 to 4 meters in diameter.
The shell destroyed the escarp and counter-escarp walls 5-6 meters in length and about 4 meters in height.
In one case, the outer wall of the scarp gallery, 1, 3 meters thick, was breached, and the inner wall was not seriously affected.
Since the 380-mm naval gun had great power and a very long range of fire (38 kilometers), the Germans often used it to bombard cities, and in particular to bomb Verdun.
On June 4, 1915, about thirty such shells were fired at this city.
The shell fragments, accompanied by many stones, are scattered to the sides for 200 - 300 meters. The screw bottom, which is 12 cm thick and weighs 54 kg, is almost always unharmed and thrown back.
When an ordinary device hit the normal stone buildings from the side of the facade, the action of the explosive charge gases destroyed everything, emptying no less than 15-meter space, but the gas pressure quickly weakened, and already 20 meters away, ordinary walls and even partitions remained intact.
On the example of a study of a large number of Verdun houses, the following is noted:
1) If the house consisted of an attic, a lower floor and a basement, then the attic and the lower floor were destroyed by a 380-mm shell hitting the roof, and the basement usually remained intact.
2) With a similar hit in a multi-storey building, the upper floors were destroyed, while the lower ones remained intact, provided that the building materials were of sufficient quality, and the floors between the floors were strong enough.
House no. 15, rue de la Reviere, could serve as a typical example: the attic and the upper floor, which were vacated from the tenants before the bombing, were destroyed, but in the dining room, which was in the lower seniority, the suspended objects remained intact, and there was nothing in the kitchen broken. In a neighboring house, damage to the lower floor appears to have been caused by a collapse of the floor slab caused by a shell explosion and furniture falling from the upper floor and attic.
In the Beaurepaire barracks, destruction only affected the attic and the upper floor, and was stopped by the arch of the next floor. Likewise, at the Buvignier School, the upper two floors were destroyed, but the lower one remained intact.
In the absence of underground shelters, the French recommended sheltering from 380-mm shelling in the rear corridors of the lower floors of multi-storey barracks, as well as in the vaulted cellars of houses (subject to strengthening - as will be said later - from the threat from 305-mm shells). On the earthen coverings of casemates, it is necessary to make slabs that can absorb explosions.
380-mm shells were fired on buildings of type No. 2, apparently, only a superficial effect. Probably, these shells (and not 420-mm) should be attributed to relatively weak destruction of casemates, as well as a powder magazine, reinforced by type No. 2. There were craters 0.6 meters deep and 2-3 meters in diameter, and from 2 shells hit almost simultaneously - craters about 1 meter deep.
The gallery connecting the aforementioned casemates was simply covered with a slab of special concrete 2 meters thick. The concrete cracked from the impact of the shell, and large pieces of it, up to ¼ cubic meters. meters each, were repulsed from the vault and from the retaining wall. When a 380-mm bomb hit, the effect of the sand interlayer between the concrete slab and ordinary masonry turned out to be very significant, because in the casemates reinforced with a layer of sand and a concrete slab, there were no signs of damage to the concrete.
One 380-mm projectile made a funnel in a reinforced concrete vault 1.6 meters thick above the gallery located between the casemates, which caused a swelling of about 0.1 meter and 4-5 meters in diameter on the lower surface of the vault.
In similar conditions, in another fortification, a 380-mm projectile hit the arch of the gallery between the casemates, forming a crater about 1.8 meters in diameter and 1 meter deep. It was accompanied by swelling of the lower surface of the vault at a height of 0.6 meters and about 2 meters in diameter.
On February 27, 1916, one similar projectile hit a 1.5-meter-thick slab overlapping shelter No. 15 and formed a larger crater, accompanied by crushing of reinforced concrete and breaking most of the metal reinforcement.
Similar results were seen on June 21, 1916.elsewhere in the concrete corridor at the casemate.
305 mm shells
Full weight 383 kg, explosive charge - 37 kg.
In embankments, 305-mm shells produced craters from 3 to 8 meters in diameter and 2 to 5 meters deep.
Type 1 structures were penetrated by this shell; it could explode even before breaking through the vault, but it usually exploded in the vault, and sometimes even below it, and the explosion was so strong that the facade walls (or walls of similar resistance) toppled over. In the barracks of one fort, the upper floor of which was separated from the lower only by a vault of bricks 0.22 meters thick, after only 3-4 hits, the shells penetrated into the lower floor. However, it can be assumed that with a lack of deep shelters, relative safety against short-term and not very intense shelling by 305-mm shells would be represented by the rear galleries of the lower floors of storey casemates made of ordinary masonry, covered with earth, provided that the partitions in the lower part of the casemate are seriously strengthened and when placed on the upper floor (previously supported) of a layer of sand, gravel or small stones. This backfill is necessary only over the protected part and should have a thickness of 3 - 4 meters.
It is impossible to note with certainty the effect of 305-mm shells on type No. 2 and type No. 3 shelters, since these shells were fired simultaneously with 380- and 420-mm shells, and it was not possible to accurately determine the destruction caused by them.
It should be noted the effect of one 305-mm projectile hitting a 1.5-meter reinforced concrete slab overlapping the double wardrobe trunk: an entrance funnel 0.5 meters in diameter and 0.3-0.4 meters deep was formed; then the projectile exploded in the slab, crushing the concrete and cutting through the iron reinforcement, as a result of which a spall appeared on the lower surface of the slab at 0.2-0.3 meters deep with a diameter of 1.5-1.8 meters.
