The Coking Industry Report on Germany

I. Forward

1. The coking industry was vital to the German war economy not only because it furnished two raw materials essential to steel production but also because it supplied an important fuel to the armaments industry as a whole. Just as blast furnaces depended on gas and coke for steel production, producers of guns, shells, panzers and trucks depended on gas for heat treating. Thus, while the coking industry was not a primary target system for air attacks, its vital position at the source of munitions production warranted an examination of its relative vulnerability to bombing. Because of the customary proximity of coking plants to steel and synthetic oil producers, the industry was sufficiently heavily hit to permit some analysis of bombing effects.

2. The Ruhr was responsible for about 70 percent of coke as well as 70 percent of steel production for Germany at the start of the war. Out of 115 German plants, 82 were located in this area. (Other districts were Aachen, the Saar, Upper Silesia and Lower Silesia.) It is important to understand, however, that although geographical concentration was great, no one plant produced more than four percent of the total output of coke. These plants were important segements; along with steel, synthetic oil, benzol and armaments producers, of the industrial complex which was constructed upon the great coal mines of the Ruhr. Because of the industrial interdependence of these segments, it is difficult to determine with exactitude their relative vulnerability to bombing as reflected in output. A disruption of inter-plant transportation or a reduction in gas or power output was often reflected in a decline of steel or armaments output. Likewise, an attack on a synthetic oil plant might by chance damage coke production more than oil production.

3. Air Attack. Air attacks prior to 1943 were not heavy and had no signficant effect on production. Attacks on the Mohne and Sarpe Dams in the Ruhr in May 1943, which caused a critical water shortage, and the heavier precision and area attacks during the first half of the year affected output moderately. The industry was not seriously hurt, however, until the final quarter of 1944 and the first quarter of 1945 when severe hits were received during the great attacks against the Ruhr industrial area.

4. Effects. The Ruhr output of coke was reduced about nine percent from the level in the three preceeding months for the two months following the May 1943 raids on the Mohne and Sarpe Dams. This effect was centered in several plants near Dortmund, which depended on resevoirs above the dams for their water supply. Production was thereafter not significantly affected until September 1944. The following table shows monthly total coke production for the Ruhr and the percent which each figure represents of average monthly production from March through August of 1944. It is clear that the decline in production, which must be in large part ascribed to the direct effects of bombing, was of highly significant proportions.

5. The following table shows the production of coke for all Germany by months during 1944 and January and February of 1945.

Although figures for gas production are not available, the evidence on hand suggests that they followed a similiar curve.

6. As was true with other industries, bombs hitting buildings containing vital equipment tended to detonate near the roof level and caused little damage to equipment. However much equipment necessary for coke production is not housed. Process piping, cooling towers, local water and power lines and coal handling conveyors proved vulnerable to air attack. Much of the production loss toward the end the war was due to damage to this equipment. Oven also were damaged by direct hits but not seriously by near misses. Direct hits by heavy bombs usually destroyed between 10 and 15 ovens. A battery consists of 60 to 80 ovens, and it was found that a portion of a battery could often be kept in operation by an ingenious management despite the destruction of a minority of the ovens. Ovens, when destroyed, generally required more time to repair than broken piping and lines.

7. Conclusions. A number of factors suggest that the hits on the coking industry in Germany were relatively effective. The industry lay at the source of almost all munitions production and its breakdown affected not only steel output but also an adquate supply of gas. The industry was concentrated in the western portion of the country and was not subject to dispersal. The actual destruction of gas production and distribution equipment which took place was frequently cited as a cause for shutdown in other industries. The fact that coke shortages were not reported is believed to have been due to decreased production in steel, which was itself in large part the result of gas shortage. In considering the effectiveness of damage to this industry, however, it should be kept in mind that coke plants were not isolated or easily segregated from other industrial enterprises and as targets were consequently better suited to area attacks than precision attacks.

II. Description of a Byproduct Coke Plant

1. Coal Preparation. Coal is usually delivered to a coke plant from the collieries by rail or conveyor. A blend of several different types of coal is usually used to improve the quality of coke for use in blast furnaces. The several coals are usually crushed 80 that 80 to 90 percent will pass through a screen an eighth of an inch thick. The crushing of coal aids in securing a homogeneous blend and eliminates the occurrence of fractures in the resulting coke which might be caused by large pieces of slate or stone inevitably found in mined coal. The crushed and blended coal mix is then usually conveyed on a rubber conveyor belt by a long steel gallery to the top of a coal bin which may serve one or more batteries.

2. Battery Operation

a. A battery of coke ovens may contain from 25 to 80 oven chambers, depending on the size of the blast furnace it serves or other production requirements. The oven coking chamber (Exhibit A) is a large rectangular slot built of silica brick. The walls of the oven chambers contain 25 to 30 vertical openings of "flues" in which gas is burned, and the heat released by combustion is carried through the flue walls to heat the coal in the adjoining oven chambers. In modern ovens, each wall heats in two directions, so that the number of walls required is one more than the number of oven chambers, since the two end walls dissipate half of their heat to the "pinion" walls. The dimensions of modern ovens chambers may vary as follows:

(1) Width - 14 to 24 inches. Average width 18 inches.
(2) Height - 10 to 14 feet. Average height 12 feet.
(3) Length - 40 to 45 feet. Average length 42 feet.

b. The air for combustion of gas in the vertical flues is preheated in "regenerators" located beneath the oven chambers. A high thermal efficiency for combustion is secured by cyclic reversal of the gas and air regenerators each half hour. the hot waste gas is then used to heat the regenerator checker brick until it can no longer absorb heat; the combustion cycle is then reversed to permit air for combustion to absorb heat from the hot checkers while the waste gas is heating regenerators from which heat has been abstracted by air in the previous cycle.

c. The brickwork in a coke oven is quite complex since 600 to 800 different shapes of silica brick are required for each oven. Replacement of damaged walls is a time-consuming process since six to eight weeks are required to manufacture the shapes, two to three months are needed to rebuild the walls and six to eight weeks are needed to heat the new repair before it can be placed in operation.

d. The roof of the oven chamber has a number of openings, three or more of which are used to feed coal to the empty oven, while one or two openings are used to permit escape of gas and byproducts. (Exhibit B) Coal is drawn from a large coal bin containing at least a 24-hour supply for the whole battery (2,000 to 3,000 tons) and deposited in a hopper larry car which is motor driven and travels on rails over the top of the entire battery. The larry car contains as many hoppers as there as there are charging holes in the oven. After the coal is dropped into the narrow oven chamber, the heat from two adjoining walls distills the volatile matter from the coal and the spongy coke is left as a residue. The rate at which coal can be distilled (coked) in an oven depends on the temperature maintained in the flues and the rate usually employed in the production of blast furnace coke is about one inch an hour. At this rate an oven 18 inches wide will complete the coking cycle in 18 hours; then the oven doors are removed and the pusher machine is used to push the incandescent cake of coke into a steel car for quenching. Since the hot coke is quenched with water, large quantities of steam are rapidly liberated and the characteristic white plume of steam from a coke plant quench can be seen for many miles.

3. Byproducts Recovery

a. The hot gases distilled when the coal is heated in the oven chamber escape through openings in the roof into tall "ascension" pipes. (Exhibit 2) The ascension pipes discharge the hot gas (1,400ƒ F) into a collecting main where it is shock-cooled to about 180ƒ F. The gas is then drawn through the suction main to the primary coolers. Large centrifugal gas pumping engines (exhausters) are used to "draw" the gas from the Ovens. through the primary coolers by "suction" and then compress the gas to provide energy to "push" the gas under pressure through the remainder of the string of byproducts equipment.

b. Tar is removed from the gas by shook-cooling in the collecting mains and by electrical precipitation. Ammonia is removed from the gas by absorption in cooling water and by reaction with sulphuric acid in the saturators. Light oil is recovered by counter-current scrubbing with absorbent wash oil in benzol washers. Ammonia absorbed in water is recovered by distillation in the ammonia stills. The light oil scrubbed from the gas in benzol washers is freed from the absorbent oil in a wash oil still to permit recyoling of absorbent oil. The final cooler is used to oool gas heated by compression in exhausters and by reaction with acid in saturators before gas goes to benzol washers. The percentage of light oil recovered from gas by washing with absorbent oil is increased by cooling the gas in final cooler. The residual coke-oven gas remaining after recovery of byproducts is then compressed for transmission to steel plant furnaces or the gas grid.

c. Exhibit C has been added to offer a more detailed flow diagram of the byproduct coke industry and to indicate the relation of coal carbonization to industry.

III. The Prewar By-product Coking Industry

1. Location

a. The byproduct coking industry of Germany is located in mining districts near the sources of the best qualities of coking coal. In contrast to the American coking industry most of the German coking plants are located at or near collieries and in close proximity to the steel mill to which coke and coke-oven gas are furnished. The individual plants in the industry are located in four main districts: the Ruhr, Aachen, the Saar and Upper and Lower Silesia. (Exhibit C) This report deals chiefly with hard coke for metallurgical and chemical uses.

b. In most cases coke is transported by rail and coke-oven gas is piped either to the neighboring steel plants or to the grid gas system. Conveyor systems are used to transport coke whenever the steel plants are close enough to the coking plant to warrant their use.

2. Principal Units. The Ruhr district was the most important coking industrial district in Germany with 82 plants (out of a total of 115) producing approximately 70 percent of the total output of coke. The nine most important plants in the Ruhr area are shown in the following table:

3. Degree of Integration

a. Because of the dependencies of the steel industry upon the coking industry for supplies of coke and gas, there was a high degree of integration between the two industries. Some individual coking plants were independently owned, but the industry as a whole was controlled by groups of coal and steel syndicates. The most important of these syndicates was the Gelsenskirchener Bergwerke A G (G B A G), which controlled a large part of the coking industry in the Ruhr and was divided into separate groups with offices in Dortmund, Gelsenkirchen and Hamborn. The central administration of this trust was in Essen. The various plants of the trust produced nearly 25 percent of the total output in the Ruhr District. More than half of the coke plants in Germany were controlled by large producers as shown in the following table:

b. Although normally the Gelsenskirchener Bergwerke AG was a private trust, its control by the Reich (and the Nazi Party) was almost complete. The same is true of the Reichswerke group, which embodies the Hermann Goering plant. Thus the government had close control of over 20 percent of the German coke industry and expanded its central coking plants (Hansa-Nordstern-Goering) somewhat at the expense of other private corporations.

4. Prewar Production. No prewar production figures were procured by the survey on coke, coke-oven gas and by-products of the coking industry in Germany. However, a report entitled "The Hard Coke Industry of Germany and German Controlled Europe" prepared by the Ministry of Economic Warfare gives the following production data:

5. Raw Material

a. Coal is the most important raw material used in the coking industry. The industry is almost entirely independent of other raw materials, since it can use blast furnace gas or coke breeze as additional sources of fuel to generate steam and power required to operate the plant. Approximately 47 percent of the coke-oven gas produced in the Ruhr in 1943 was used in the steel plants; the balance was available to the Ruhr gas grid.

b. Second in importance to coal in the coking industry is the supply of water which is used in the chemical process to produce steam and power and to cool and clean the hot coke-oven gas.

c. Lime, sulphuric acid and wash-oil are used in the chemical process but they represent only about 1.5 percent of the requirements of raw material.

d. In the recovery of byproducts, most of the coke-oven gas was purified with iron oxide, and the sulphur removed from the gas was recovered from the spent iron mass. The most important prewar source of sulphur was in Italy, and the difficulties in importing sulphur necessitated the recovery of sulphur from spent oxide. In peacetime, spent oxide is discarded. The quantity of sulphur recovered was small but important.

6. Use and Distribution of Finished Products

a. The principal function of a coke-oven plant is to supply coke to the steel and chemical industries. These are largely dependent upon byproduct coke for operations and consumed about 50 percent of the total prewar output. Since Germany has no natural gas or oil supplies, many of the larger cities in central Germany have large byproduct coke plants for the production of coke-oven "city" gas. Accordingly the overall output of coke-oven gas was well in excess of the normal requirements of the steel industry. In peacetime, industry consumed about 50 percent of the coke produced, in Germany, and the remainder was used for domestic purposes. In the 'United States industry consumes about 80 percent of the total coke production, and the remainder is used as domestic fuel. Thus we see that Germany had a very large reserve of domestic production to draw on for her wartime emergencies.

b. In the past 25 years most of the byproduct coke plants in Germany have been connected to the Ruhr gas grid, which transports the surplus gas from Ruhr plants to other industrial areas and to urban points of consumption. The Ruhr gas grid, prior to 1939, extended east from the Ruhr to Hanover; but with the construction of the Herman Goering Works at Salzgitter in the beginning of 1940, the gas grid was extended farther east to Berlin. Separate gas grids of lesser importance have been developed in the Saar basin and Upper Silesia. Satisfactory coupling of the various grids was never completed. Compressor capacity and pressure limits, combined with heavy concentration of gas production in the Ruhr, did not permit prewar hopes for flexible gas distribution to be fully realized.

c. Demands for coke-oven gas grew, even in peacetime, as the grids were extended, so that most coke plant tried to release to the grid as much surplus coke-oven gas as possible. In the operation of a battery of ovens, coke-oven gas, blast furnace gas or producer gas may be used as fuel to carbonize the coal. Where coke-oven gas is used in underfiring, approximately 40 to 50 percent of the gas produced from carbonizing coal must be recycled to keep the ovens hot. Where coking plants are located near steel mills, large quantities of blast furnace gas are available and easily piped to underfire coke ovens.

d. Since blast furnace gas, because of its heating qualities, is a less desirable fuel for most steel plant furnaces, its use for heating coke-ovens results in a marked increase of efficiency and revenue by the release of total coke-oven gas produced. Somewhat the same situation applies to producer gas made from small sizes of coke. The coke plants at which blast furnace gas is not available may generate producer gas from coke to underfire the ovens and thereby release larger quantities of coke-oven gas for other commercial and domestic consumption.

e. Every effort was made to recover the maximum of light oil, tar, ammonia, and suphur. Although byproducts other than gas represent only five to six percent of the weight of coal carbonized, their uses are extensive. Before the war continental Europe and England utilized benzol as a major source of motor fuel. The high anti-knock qualities of benzol are well known and in the United States it is an important source of cumene (used for aviation fuel), styrene (used in the manufacture of synthetic rubber and plastics), phenol (plastics and resins) and many other compounds. Toluol is also well known as an important raw material for the manufacture of trinitrotoluol (TNT).

Tar is not only used as a source of fuel, road paving, creosoting, etc., but in Germany it was an important raw material in the manufacture of synthetic gasoline. Ammonia is of course extremely valuable as a base for explosives and fertilizers. Some of the coke plants were associated with plants producing hydrogenated synthetic motor fuel by utilizing the hydrogen content of coke-oven gas. The Ruhrchemie plant at Sterkade piped coke-oven gas from the Osterfeld coke plant to their hydrogenation vessels, reacted vapors with coke-oven hydrogen and returned residual methane to Osterfeld for use as fuel. The recovery of sulphur was mentioned above and a myriad of uses for coke-oven byproducts might be mentioned, if space permitted.

7. Labor Requirements

a. The labor forces in the industry increased from about 13,000 employees in 1932, to about 24,000 employees in 1937. This was due to the fact that coke production was advanced to meet increased requirements of the steel industry and the increased demand for coke-oven gas for other commercial and domestic purposes. Thus, labor requirements of coke plants do not loom as an important factor in the overall war economy. The amount of labor required in coke plants, however, is extremely small in relation to the large tonnage of material processed by the plants.

b. The following table shows the total labor force in the industry from 1932 through 1937:

c. No figures were available on the total number of employees in 1938 and 1939 just prior to the outbreak of war in Germany.

IV. Planning for Industry in Wartime

1. Government Control and Ownership. Ostensibly there was no government ownership in the coking industry during the war. Reference is made, however, to vertical trusts mentioned earlier in this report (Gelsenkirchener Bergwerke-Reichswerk).

2. Expansion of Facilities

a. According to available information during the years 1939-1945, approximately 2,000 or more coke ovens with a total annual capacity of 10,000,000 metric tons of coke were constructed in prewar Germany. Slightly less than one-half of these ovens were built to replace existing facilities which had worn out, while the balance were used to further increase production. A small number of the facilities used to increase production was built in central and southern Germany to serve steel mills and city gas plants in those areas.

b. One of the most important wartime expansions of the German industry was the construction of the Herman Goering Works at Salzgitter, Braunschweig and Linz, Austria. Construction of the Goering Salzgitter plant began in 1940 with four batteries totalling 220 ovens, and in 1944 two more batteries (110) ovens were added. It was planned to start construction on two additional batteries totalling 110 ovens in 1945. A total of 440 ovens would have made this the largest coking plant in Germany.

3. Dispersal and Relocation

a. Except for the construction of the Herman Goering works, which is away from the coking industry area, there were no significant moves made to disperse any coking plant from the important Ruhr, Saar and Silesia areas. This type of industry does not lend itself easily to dispersal because of the impracticability of dismantling the existing facilities. In addition, the increased difficulties in transporting coal over long distances would have made large-scale dispersal of the coke industry very impractical. Despite all efforts of the German government to force dispersal of the industry, relocation never reached significant proportions during the war.

b. Data on new coke oven construction from a leading German builder indicate that expansion in the districts just mentioned, after making allowances for replacement of worn-out facilities, was approximately as follows:

* See Table 3 showing coke production for 1938
# Using data on Upper and Lower Silesia quoted in Table 3 for 1938 and Table 6 for 1944, it would appear that Silesian coke production was increased about 4,000,000 tons per year. This productive capacity must have been built by sources other than those quoted in this production table.

c. The only district in which production was disproportionally increased was the Saar-Aachen district, where the increase was about 20 percent. Since this district only produced about 10 percent of the total German coke production, the shift is not significant. Data from a source which cannot be verified indicate that productive capacity of Upper Silesia was increased during the war from about 3,400,000 metric tons per year to about 6,000,000 metric tons per year. In addition, Austrian coke capacity was increased by about 2,000,000 tons per year and Czechoslovakian capacity was increased about 1,500,000 tons per year. German coke plant construction in France, Belgium and Holland did not reach significant proportion during the war. The total expansion of coke plant facilities was greater during the war than the corresponding expansion for American facilities.

4. Stockpiling. Because most of the coke plants were located short distances from mines supplying coal, there was no necessity of stockpiling coal on a large scale. Small company-owned rail lines were used to transport coal over short distances, and the national transportation system was only relied upon for long distances. By the same token, no significant stockpiling of coke occured at the steel mills. In the Herman Goering Works at Salzgitter, coal was stockpiled in the latter part of 1944 on account of increasing transportation difficulties, and large piles of coke also accumulated at some plants during the latter part of the war.

5. Importance of Industry. Because of the importance of the steel industry in the war plans of the German General Staff, and the dependency of the steel industry upon the coking industry for supplies of coke and gas, the coking industry was an important factor in the conduct of the war. Without coke and gas the steel plants would have been unable to produce steel for the implements of war, and the whole of Germany's war effort would have been seriously threatened.

V. Performance Of The Industry During The War

1. Planned Productino and Plant Capacity. Because of the chemical process used in this type of industry, which requires a constant flow of the output, planned production was based on a day-to-day schedule set up for equal amounts to be produced each day. Until the fall of 1944, when increased air attacks in Germany began, most of the plants seldom operated at full capacity. From September 1944, however, repeated bombings on the plants, transportation facilities, gas lines and water lines began to seriously affect the output of individual coking plants so seriously that their full capacity had to be utilitized. The coking rate in most of the German plants visited was less than one inch per hour. This means that the German coke industry could regain a portion of production loss suffered from air raid damage to ovens by speeding up unharmed batteries. Damage to byproduct equipment would be recoverable, and over plant capacity would still be goverened by the quantity of gas which could be handled in the undamaged parts of the byproduct plant.

2. Actual Production. The following table shows the annual production in Germany from 1940 through the first eleven months of 1944:

Note: No direct figures showing production of coke-oven gas or byproducts were available.

3. Changes in Processes. There were no planned or actual changes in the process of producing coke and coke-oven gas. Also, no significant shortages of coal existed to necessitate any change in the process of producing coke and gas. Steps were taken, however, to insure the maximum recovery of coke-oven gas and byproducts through auxiliary installations.

4. Production Loss

a. Air attacks on the Mohne and Sorpe dams in the Ruhr area in May 1943, were the only attacks in that year which had a widespread effect on the coking industry. This effect was greatest on several individual plants in the Dortmund area, which drew their supply of water from these reservoirs, In the two months following these raids, the Ruhr output of coke was reduced by approximately nine percent per month based on the daily average for February, March and April of 1943. After repairs were made to water lines, production began to increase, and by January 1944 the pre-raid level was reached.

b. The total loss In production as a direct result of these raids in the eight months period from 1 May 1943 to 31 December 1943 was only 397,199 metric tons of coke or the equivalent of .13 months of the average pre-raid Ruhr production. (Exhibit D)

c. The combined bomber offensive, which began in midsummer of 1943, did not begin to affect the coking industry as a whole until September 1944 because:
(1) Areas where plants were located were not subjected to heavy attacks.
(2) Neither the individual plants nor the coking industry as a whole was considered a primary target for bombing.
(3) Each individual plant represented only a small part of the production of the coking industry.

d. Saturation raids on the Ruhr district, which was producing 70 percent of Germany's total coke output, during the last three months of 1944 seriously curtailed coke and coke-oven gas production in most of the plants in this area. Because of the location of the coking plants within the highly industrialized Ruhr target area, many bombs fell on coking plants, inflicting serious damage to installations and causing losses in production from which the industry was never able to recover. (Exhibit D)

a. The loss in Germany's Ruhr coke production from 1 September 1944 to 31 March 1945 was 10,308,124 metric tons, based on the monthly average production for the six month period from 1 March 1944 to 31 August 1944. This is equivalent to three and four-tenths months or about 50 percent of production at the pre-raid monthly average. (Exhibit D)

f. No direct data were available as to the losses in production of coke-oven gas and byproducts. Since the quantities of coke and gas produced, per ton of coal charged, follow a somewhat fixed relationship, it may be concluded that all air raid damage to byproduct equipment and gas lines resulted in at least a proportionate loss of as compared with losses in coke production. (See Table 6 for estimates of total German gas and byproducts production by years.) It is possible, of course, to continue to produce coke and waste the gas if the byproduct receiving equipment is sufficiently damaged to limit receiving of gas and the ovens can continue to operate. The figures in Table 6, however, indicate that this was not accomplished.

5. Air Raid Damage

a. Air raid damage to vital buildings due to high explosive bombs was generally limited to extensive destruction of roofs with little damage to vital machinery housed in the buildings. This type of damage was apparently due to fuzing which caused bombs to detonate shortly after impact on the roof. The density of buildings in a coking plant is very low compared with that of other industries. Consequently, most of the buildings suffered only superficial damage.

b. On account of operational problems, most of the piping, towers, stills, etc, at a coking plant are installed outside of buildings. Usually, only prime movers, pumps and instruments are located inside.

c. Several ovens were damaged by direct hits of high explosive bombs. Near-misses on coke-oven batteries had little effect, because heavy steel had been used to bind the battery brickwork. The effect of near-misses of heavy bombs was usually limited to the destruction of one or two oven walls or to destruction of about 10 percent of the end brickwork of five to ten ovens. Repairs on end flues were readily made, with the result that there was little loss in production. Direct hits by heavy bombs penetrating the oven roof and exploding in the oven chambers usually ruined 10 to 15 ovens. Since oven walls are not tightly bonded by the refractory mortar used in laying brick, the oven brick cushioned the effect of bomb concussions somewhat in the manner of dry brick walls. The weight of brickwork In a coke-oven battery will run from 10,000 to 15,000 tons; therefore a heavy weight of bombs is required to ruin such a structure. Despite the loss of 10 to 15 ovens through air raid damage, most plants continued to operate undamaged ovens in the battery hit by a bomb.

d. Except where direct hits were scored, very little damage to exhauster machines, the nerve center of a coke plant, was observed. This was largely due to the weight and thickness of metal used in the construction of .the machines as well as the protection of dry brick walls. In most cases of heavy bomb hits on exhauster buildings, the bombs exploded shortly after penetrating the roof and even when the roof members fell on the protecting walls, the machines were not seriously damaged.

e. The most marked effect of high explosive bombs was observed in process piping and cooling towers. The piping and towers usually are made of plate a quarter of an inch to five-sixteenths of an inch thick, which is readily damaged by concussion and bomb fragments. Gas cooling and absorption towers are usually slender, quite tall and lightly braced, so that blast effects are quite conspicuous. The wood hurdles or slats, in benzol washers, also contain absorbent oil and combustible gas; fires are therefore easily started and difficult to control. Air raid damage to byproduct piping and towers was widespread, but loss in production was limited because the towers were operated in groups of two to six towers with bypass piping provided to isolate any one tower. Provision of spare towers and bypass piping is normal for coke-oven construction in all countries.

f. Damage to coke wharfs was very limited and repairs were easily made.

h. Incendiaries caused some fires in byproducts areas, but their maximum effect was obtained when high explosive bombs ruptured vessels containing inflammable liquids and caused fires to spread.

i. The damage to raw material was never significant since only light damage was inflicted on coal stocks in some plants where these stocks were maintained. The supply of coke available to chemical industries in Germany, after requirements of the steel plants were filled, was adequate for war needs.

j. There were very few casualties in the whole industry, either killed or wounded, because of the small number of persons employed in each plant and tbe excellent air raid shelters that were provided.

6. Absenteeism and Efficiency of Labor

a. No serious labor shortages or absenteeism existed in the coking industry on account of the abundant supply of foreign slave labor. Large slave labor camps were usually located in most of the large industrial areas, and the various plants could draw on these camps for their labor supply. In 1944, as many as 75 percent of the workers in some plants were foreign slave laborers.

b. In order to maintain the efficiency of the plant and prevent sabotage or serious damage to installations, it was considered by plant officials that a minimum of 25 percent of the labor force must be German workers.

a. During air raid alarms the slave laborers immediately went to shelters, while the German supervisory force was required to remain at or near their stations. A coke plant can be very effectively damaged by internal gas explosions in case of steam or power failure if operators forget to close the correct valves in a complicated sequence of operations. The necessity of maintaining a minimum force of German workers is quite obvious.

d. Plant officials stated that losses of coke plant workers due to Army drafts amounted to less than five percent of the total labor force.

7. Transportation. Generally speaking, the transportation of coal from collieries to coke plants and of coke from coke plants to steel mills was not seriously affected by bombing until early in 1945. The existence of a complex Ruhr railroad network, owned and operated by the steel and coke syndicate, facilitated movement of coal and coke.

8. Intelligence Estimates of Production Losses. In most cases Intelligence underestimated loss of production by 10 to 20 percent.

9. Air Raid Protection

a. Workers had the advantage of excellent air raid shelters and protection in most of the plants. In many plants air raid shelters were set up under the coal bins. These bins were about 100 feet high and were usually filled with coal, which provided additional overhead protection. First aid stations were provided in nearly every plant. Portable and fixed fire fighting equipment was available in nearly every plant. Secondary damage due to explosives in gas lines was negligible because of the well-trained ARP supervisory force.

b. Blast walls of dry-laid brick were particularly effective in absorbing the effect of high explosive concussions and shielding vital machinery from bomb fragments and concussion. The walls were usually 12 inches thick, built of loose brick to a height slightly higher than the machine. In cases where roof trusses were blown down, the walls would suspend the trusses above the machine. During early raids (1942-1943) small concrete huts were located above ground near important valves or machinery, and watchers were paid bonuses to extinguish incendiary and other types of fire. The impression was given that deeper shelters were built in 1944, and that workmen did not wish to be above ground in huts when very heavy bombs were being dropped.

10. Diversion of haw Material There was no evidence to indicate that raw materials were diverted from the coking industry to other industries with a high priority for coal. The supply was always adequate in the coking industry.

VI. Summary Of Bombing Attacks On The Industry

Left - Boesch-Kaiserstuhl Coke Plant. Wooden timbers at top of photograph used to bridge ovens and permit operation of remaining ovens.

1. Attacks. Although the steel industry could not operate without the coke and coke-oven gas supplied by the coking plants, few instances were found in which the plants in the coking industry were considered as a primary target for attacks. Because of the integration of coke and steel plants and the proximity of coke plants to synthetic oil plants and large cities, the coke plants were, in most cases, hit by bombs from raids directed towards the abovementioned targets.

2. Vulnerability

a. The most far-reaching and permanent damage that can be inflicted on a coke plant is the complete destruction of the coke oven batteries. A coke oven contains anywhere from 25 to 80 ovens, depending on required capacity. A different opinion on the extent of bomb damage required to effect total shutdown of an oven battery was expressed by a previous survey team which examined two Belgian coke plants in January 1945, one in Montigny and the other at Liege. The Montigny plant was found to be at a standstill for four entirely separate reasons, env one of which might have been sufficient to render the entire battery inoperative:

(1) Direct hit on coke oven battery.
(2) Destruction of water supply areas.
(3) Destruction of coke handling apparatus.
(4) Destruction of coke wharf and coke car track.

In Report 13 of the Weapons Effectiveness Section of the U S Strategic Bombing Survey, under the heading of "Comments on Bomb Damage," the following statement appears: "It can therefore be accepted that any bomb of this size and fuzing (500-lb GP bomb, fuzed .025 seconds delay), detonating within an oven chamber, can be relied on to effectively destroy the battery to which this oven belongs".

Right - Hoerder Coke Plant. Details of brick columns supporting larry car rails to permit operation of remaining ovens.

b. An opposite conclusion reached by members of the Munitions Division of the Survey after visiting representative German coke plants was that a direct hit by a heavy high explosive bomb will destroy only 10 to 15 ovens if the bomb penetrates the oven roof end and explodes in the center of the brickwork. The remaining ovens in batteries struck in this manner were usually back in operation in a short time. Photographs taken at the Kaiserstuhl and Hoerder plants show construction of shoring in damaged ovens to support larry car rails so that coal could be charged to remaining ovens. It was further found in Germany that it took as many as three direct hits, properly spaced, to ruin an entire battery of 60 to 80 ovens.

c. Another example of steps taken in Germany to keep a battery in operation, although the battery had suffered a direct hit, was the temporary filling of the oven walls with brick to provide support for the larry car track. In short, it seems that where there is a will to continue to operate a battery, temporary repairs and improvisations will permit the remainder of a battery to operate, although as many as 10 to 15 ovens have been seriously damaged.

d. In general, it has been found that serious damage to water, steam and power lines is effective in stopping plant operations. Unless the primary source of such utilities is completely destroyed, repairs can usually be made in time to permit resumption of operation in one to three weeks.

e. Coal handling conveyors were found to be vulnerable to air attacks, and damage to them at several of the plants visited played an important role in curtailing production.

f. Gas piping and cooling towers were found to be the most vulnerable part of a coke plant; damage at these points resulted in prolonged production losses.

g. A coke plant needs coal as badly as it needs utilities, and a very vulnerable point is the coal gallery carrying coal from mixing bunkers to the oven bin. The conveyors are usually supported by tall structural steel work in order to reach the top of the coal bin. High explosive bombs, in several instances, collapsed the coal carrying gallery and put the batteries affected out of operation for at least two or three months.

h. It was noted that HE bombs had a very marked effect upon the process piping and cooling towers because piping and towers are easily damaged by concussion and bomb fragments. Gas cooling and absorption towers are usually slender, quite tall, and lightly braced; effects of blast on the towers are quite marked. In addition, most of the towers are filled with wood hurdles or slats. In the case of benzol washers, the wood-filled towers also contain absorbent oil and combustible gas; fires started here are very difficult to control.

i. A serious break in the train of byproduct gas piping or the collapse of one or more towers will interrupt the entire gas cycle and seriously affect both coke and gas production. The towers are operated in groups of two to six, with bypass piping provided to isolate each tower. If the damage inflicted is widespread enough to destroy the bypass and main lines, none of the towers can be bypassed, and the flow of gas will be cut off and the production of coke and gas greatly reduced. In several plants investigated this damage was widespread and production was curtailed.

j. Towers and piping of the benzol plants for the recovery and refining of light oil are subject to damage. In addition, benzol plants are distinctly vulnerable to air attack, on account of the presence of highly inflammable liquids and vapors. In quite a few instances, hits by high explosive bombs did not secure maximum effectiveness because fires did not break out when oil lines were broken. Incendiaries accompanying high explosive bombs tend to increase the effectiveness of air raids on benzol plants, whereas elsewhere in the coke plant incendiaries had little, if any, effect.

k. At one plant (Hoerder) complete destruction of the coke screening station seriously hampered the flow of coke from the batteries to the blast furnaces and railroad cars. In this case, production was seriously retarded until temporary coke handling equipment could be provided.

Above - Carolinen Gluck Coke Plant. Photographs hsow destruction of gallery conveying coal to two batteries of coke ovens.

l. On the whole, the individual coke plants were scattered over a widespread area in Germany. However, since 82 plants out of an estimated total of 115 in the industry were located in the Ruhr district (which is about 40 miles long and 20 miles wide) and produced 70 percent of Germany's coke, it would seem that the Industry was extremely vulner able to air attack.

VII. Conclusions

1. During 1943 and 1944, the coking industry in Germany was never a primary target or a part of a primary target system for bombing attacks. The majority of the raids in which bombs hit coking plants were directed against the nearby steel mills, synthetic oil plants and industrial centers in the areas, and coking plants were hit by spillover bombs from these raids. Saturation raids, which began in September 1944 in the Ruhr area, where 70 percent of the German coke production is located, resulted in a decrease in production from 35,541,000 metric tons in 1943 to 31,687,000 metric tons in 1944. Prior to 1943, there were no raids there and no loss in production of coke. In the coke industry as a whole, there was no loss of production in the first part of 1944. The following table shows the amount of coke produced per month and the percentage of the pre-raid average for the first six months of 1944 represented by the monthly production from 1 September 1944 to 31 March 1945:

2. After the saturation raids began in 1944, production of the entire Ruhr coking industry decreased steadily from month to month until the occupation of the area by the Allied armies.

3. Production of coke and coke-oven gas was never seriously affected by attacks on other industries, except for the attacks on the Mohne and Sorpe Dams in May 1943. While there was a temporary loss in production in some individual plants, the industry as a whole quickly recovered these losses.

a. The total loss in production of Ruhr coke, as a result of bombing, from 1 May 1943 to 31 December 1943 amounted to 387,188 metric tons, or .13 months of the pre-raid monthly average. Water lines were repaired and production in the industry began to increase until the pre-raid level of production was reached in January 1944.

b. Since individual plants were located near the mines from which coal was secured, the industry can be considered self-sufficient; it was not dependent on any other industry for supplies of raw material. Sulphuric acid was used in the chemical process, but it represents only about one and a half percent of the total requirements of raw material for the industry.

4. Pre-raid Intelligence was in possession of all of the important information with respect to the coke industry, The reasons for this are: (1) Substantial information on the prewar position of the coke industry was available to Allied Intelligence, (2) Coke is produced by the same processes throughout the world. (3) It is easy to estimate the output of a plant from photographs by counting the number of coke ovens. (4) Coke plants cannot be dispersed, camouflaged, or effectively used for any other purpose.

a. Pre-raid Intelligence was accurate in its estimates of production for individual plants as well as for the entire industry. Photo interpretation was generally accurate in judging plant layouts, but erred in details in the byproduct sections. Since coke plants were never attacked as primary targets, they were not studied so carefully as in other industries.

b. Post-raid Intelligence based on aerial cover was not so accurate as pre-raid Intelligence. For instance, some immediate interpretation reports claimed that coke ovens had been set on fire. This is impossible because they are of 100 percent fireproof construction. Estimates of physical damage were a bit too conservative in most cases, assessments of losses of production, both in particular plants and in the industry as a whole, were 10 to 20 percent below actuality.

5. Even though there was a loss in production, there was no reduction in the quality of the product resulting from the use of substitute materials because no substitutes can be used in an industry of this type. The quality of coke, coke-oven gas and by-products does not vary greatly, but the quantity of coke-oven gas varies with the quality of coal (volatile matter) used in production. The coal mixture used in Germany, however, was nearly always of the same type; therefore there was little variation, due to raw materials, in the quantity of coke-oven gas produced.

6. Gas piping towers and facilities in the benzol plant appear to be most susceptible to air attacks because of the amount of gas piping used and the presence of highly explosive liquids and vapors. In order to reduce production of coke for six months or more, however, it is necessary to destroy the coke-oven batteries.

7. Bypassing of damaged units in the byproducts recovery system frequently permits coke production to be maintained at a normal level with only slight loss of gas and other byproducts. This is an important factor in recuperating losses in production.

8. Light raids with incendiary bombs generally had little effect on coke plant operations, while incendiaries accompanying high explosive bombs had a tendency to increase considerably the damage to benzol plants. Equipment in benzol plants is not combustible, but the product is.

9. Destruction of coal conveyor galleries seriously reduced production at some plants out of proportion to damage the to the remainder of the plant.

10. Two of the plants visited which depend on rail transportation of coal were not hit by heavy raids until late in 1944. Correlation of production data for the first part of 1944 with data for September and October 1944 shows loss in production due to lack of transportation of 16 percent at Hansa and 13 percent at Thyssen.

11. Coke plants depend on steam, water and power for their operation, but most steel plants and collieries have both steam and power facilities. Most coke plant equipment is provided with spare prime movers actuated both by steam and electricity; thus they are particularly vulnerable with respect to all utilities except water.

12. It is difficult to evaluate the effect of reduction of the supply of coke upon other industries because the reduction was very small until the last three or four months of the war. At that time the requirements of the steel industry had decreased proportionately because these plants had also been affected by bombing and were not operating at anywhere near pre-raid capacity. Stock piling of steel ingots evidently did not make it necessary to accelerate coke production to any appreciable extent. On the other hand, gas consumption by the various gas grids is a direct barometer of war material production, and decreases in coke-oven gas production did affect war production of many other industries.

13. Because of the nature of the industry, no effective dispersal of facilities could be made. In order to disperse a coke plant, the oven would have to be dismantled; such an operation would be impractical both from the standpoint of time and expense.

14. In the Saar area, investigation of the steel plants revealed that no serious loss in steel production occured until late 1944. This was also true of the proximity of the Saar plant to the fighting front and also beause of the general breakdown of the whole German war economy at that time.

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