Appendix¹

The German Electric Power Complex as a Target System

As stated earlier, initially the German electric power system had been adequate to its demands. There was sufficient capability to permit boilers and turbine-generators to be shut down periodically for maintenance. But, by 1939, the peacetime demands were putting great strain on the capacity of the system, and with the outbreak of war the demands rose rapidly. Power was rationed first with regard to civilian non-war use. But as the demands for munitions rose, the entire reserve capacity was absorbed, and still it was necessary to ration vital industries. By 1944 many vital industries were rationed at thirty percent below their needs.

It became impossible to allow "stand down" for maintenance and this also began to be felt. Power availability fell considerably below normal "plate" capacity.

Little effort had been made to increase the power capacity at the outset of the war, since the war was expected to be of short duration. But in 1941 an attempt was made to build ten large new plants. None of them was completed prior to the end of the war. However, existing plants were expanded on the following scale:

1942 900,000 additional KW
1943 850,000 additional KW
1944 875,000 additional KW

Since the total theoretical installed capacity came to 22,000,000 KW in 1944, of which the actual peak extraction was about 16,000,000 KW, this increase in existing plant capacity was small and was hardly felt. Of the theoretical installed capacity of 22,000,000 KW, 13,300,000 KW was incorporated in the national integrated system. The remainder was either in large factory plants, in the national railway system, or in a large number of small installations which were not included in the generally available power pool.

Of the 13,000,000 KW theoretical capacity of the integrated system,

79% was in coal burning plants.
21% was in the hydroelectric power plants.

About twenty percent of the entire generating capacity was established in the industrial area around Leipzig. Another twenty percent was established in the Ruhr. The hydroelectric plants, comprising another twenty percent, were in southwest Germany.

The distribution of the more important electrical power stations came from some ninety-five power generating stations:

Over 200,000 KW	5
100,000 to 200,000 KW	40
50,000 to 100,000 KW	50
	95

The total number of large stations was 45. Their capacity was a total of 8,000,000 KW, or nearly two-thirds of the capacity of the installed integrated systems.

This complex, vital, and over-stressed system was operated under the constant control and supervision of the National Load Dispatcher in Berlin, who in turn operated through twelve District Load Dispatchers, each having a major switching system.

Actually the maximum peak capacity that ever flowed through the system rated at 13,000,000 KW was 9,700,000 KW. Thus the 45 plants with a theoretical capacity of 8,000,000 KW constituted the

great majority of power which was in such urgent demand by industry.

The integrated "grid" which was the cause of such concern to the Committee of Operations Analysts and the air planners turned out to be far less flexible than they had believed. The report of the USSBS says "A statement by the National Load Dispatcher discloses that the capacity of the transmission system was such as to permit an exchange between adjacent districts, of approximately 10 percent of the larger district's capacity." Thus the system was much less flexible than we had thought.

The report has the following to say about transmission systems:

The ability to use electric power transmitted over a transmission line depends upon rather severe limits of receiving-end voltage. Any voltage variation beyond the band of 90 percent and 110 percent of normal leads to damage of connected utilization equipment. At some value between 80 and 85 percent of normal voltage, the whole transmission system becomes unstable and will suddenly collapse with coincident wide-spread damage to utilization equipment.

When generating facilities are lost, the transmission system capacity drops at the same time because of the loss of synchronous equipment in the generating stations (turbo-generators), which was the terminal equipment of the transmission system. Destruction of generating facilities, therefore, has a two-fold effect: the direct loss of generating capacity of the area, and the simultaneous reduction of transmission line capacity into the area.

An integrated system contains a complex array of voltage regulators and relays and circuit breakers and switches intended to prevent and arrest damage which may be caused by sudden increases of load and sudden drops in capacity and voltage. These control complexes and safety devices are limited in the degree to which they can accommodate sudden major changes in load and voltage.

The complexes are usually integral with or immediately adjacent to the powerhouses, as are the large transformers.

The Bombing Survey concluded that all evidence indicates that the destruction of power generating and switching installations would

have had a catastrophic effect on Germany's war production. The survey might have added that it would have had a catastrophic effect on Germany's civilian economy and social structure as well.

Was the destruction and disruption of the German Electric Power System within the capacity of the available strategic air forces? More specifically:

(a) Could the disruption of the German electric power system have been accomplished in addition to the other operations actually carried out before the invasion, with the forces actually made available?

(b) Could the disruption of the German electric power system have been carried out in addition to the other priority objectives of the CBO, shortly after the invasion?

(c) Would the disruption of the German electric power system in addition to the other primary objectives, have "fatally weakened" the German ability to support the war and thus have brought the German state to collapse at an earlier time? What size force was required to destroy and disrupt the German electric power system?

Computation of bomber force requirements to assure destruction and collapse of the German electric power system can now be made on the basis of actual war experience, and involves consideration of a number of steps.

 

1. What is the number of generating plants and switching stations that would have to be put out of operation?

Dr. Carl, a German electric power engineer, submitted a report to the German National Load Dispatcher describing the targets whose destruction would bring about collapse of the system. His report was dated February 23, 1944.

He considered that the U.S. and British strategic air forces would be apt to attack a few transformer points between districts, such as Braieweiler and Kelsterbach sub stations. "After putting this inter-district grid out of operation, the intra-district power supply could be paralyzed by individual attacks on 56 of the most important generating

stations whereby two-thirds of the entire German power production could be eliminated."

Another German study lists nine transformer stations and forty-one generating stations.²

For the purpose of this analysis, the target systems will be taken at fifty-six generating stations and nine transformer and switching sub stations.

2. What number of hits and size bombs would be required to knock out an electric power generating station?

The typical thermal electric power station in Germany had its most vulnerable and vital elements housed in a power house about 400 feet by 500 feet in dimensions. The entire complex, including transformers, switchgear, condensers, pumps, and other equipment occupied an area of about 25 acres, or an area about 1000 feet by 1000 feet.

All the facilities were vulnerable to heavy high explosive bombs, which should have delay fuses. Five hundred-pound bombs or larger were found to be adequate to cause irreparable damage. Since no spares for heavy equipment were available, the restoration of operation would have to await manufacture of replacement equipment.

After examining twenty-five generating stations which had been damaged by air attack, the Electric Utilities Report of the U.S. Strategic Bombing Survey had this to say:

. . . from the foregoing it can readily be seen that an electric generating station or a switching and transformer station is a highly integrated mechanism, each unit playing a vital part in the functioning of the plant as a whole.

The layout in all cases covers a large area, is easily traced by transmission lines, and is easily recognized from the air. It has been demonstrated to be exceedingly vulnerable to air attack, and even a chance hit may be so damaging as to close down a plant completely. From the standpoint of generating station engineers and operating

men, the vulnerability of a generating plant to air attack in wartime is a continued nightmare.

The recuperability of a generating station to a major failure even in normal times is slow. No two plants are alike, and often the individual pieces of equipment are specially designed to meet a given set of conditions. The possibility of maintaining adequate spares to cover contingencies in such `custom-made' plants does not exist.

As indicated earlier, examination of these plants which had received damage incidental to attack on adjacent targets led the USSBS to conclude that .2 tons of bombs per acre would put a plant out of commission for several months, and .4 tons of bombs per acre would put a plant out of commission for a period lasting from 6 to 18 months.

Since a powerhouse proper averaged about four acres in extent, this would require two hits with 1100-pound bombs to put the station out of commission for several months, and 3 hits with 1100-pound bombs to knock it out for 6 to 18 months.

The entire area of the generating complex, covering 25 acres, or an area of 1000 feet by 1000 feet, should receive 10 tons of bombs or 20 hits with 1100-pound bombs to knock it out for 6 to 18 months.

3. What size force is required to knock out a generating station, as determined by actual bombing accuracy and prevailing tactics?

In computing requirements to knock out a generating plant, the current bombing tactics employed by the Eighth Air Force, that is to say, formation pattern bombing by combat boxes of 18 aircraft at 20,000 feet and the actual bombing accuracy and distribution recorded for the Eighth Air Force in 1943 and 44 will be used:

Average radial error of the center of the bombing pattern from the aiming point: 875 feet.

Circular probable error of the center of the bombing pattern about the aiming point: 820 feet.

Average dimensions of bomb pattern: 2400 feet by 2400 feet.

One combat box of 18 bombers carrying 1100-pound bombs could deliver 108 bombs.

Considering first the powerhouse only (400 feet by 500 feet), a combat box would provide a 75 percent probability of making at least 1 hit with 108 bombs.

If one combat wing (3 combat boxes or 54 bombers) is used against one powerhouse target, the probability of at least one hit is 98.5 percent, and the probability of at least 2 hits is 84.5 percent.

If two combat wings (6 combat boxes or a total of 108 bombers) are used against 1 target, then:

The probability of at least 1 hit is 99.99%.
The probability of at least 2 hits is 96.5%.
The probability of at least 3 hits is 89%.
The probability of at least 4 hits is 77%.
The probability of at least 5 hits is 54%.
The probability of at least 6 hits is 18%.

This is a conservative method of estimating probable hits.

The probability of making at least three hits with two combat wings is thus about ninety percent.

The normal expectancy (fifty percent probability) of hits within the powerhouse itself from one combat wing is eight.

Thus, if 2 combat wings (6 combat boxes or 108 bombers) attacked each power generating station, they would have virtual assurance of at least 1 hit in the powerhouse, a 96.5 percent probability of knocking it out with 2 hits for several months and 89 percent probability of 3 hits, knocking it out for 6 to 18 months.

As for the total target area: (1000 feet by 1000 feet)

The normal expectancy (fifty percent probability) of bombs within the target if two combat wings are used is fifteen percent. This would provide a normal expectancy of ninety-seven hits within the target area. Actual experience showed that fifteen percent of all bombs dropped by all methods (visual bombing and instrument bombing) by the Eighth Air Force against the oil targets fell within the target area.

4. What is the number of successful attacks and what is the weight

of bombs required to knock out two-thirds of all German electric power?

If 65 targets were attacked (56 generating stations and 9 transformers and switching stations), it would require 65 successful missions by 2 combat wings each if it were considered desirable to seek such a high probability of destruction at each target (90 percent). Since each combat wing would utilize 54 sorties and deliver 178 tons of bombs, this would involve a total of 23,140 tons of bombs delivered in daylight precision bombing by 7,020 sorties.

But even such high probabilities of success as those chosen still leave a chance that some targets will not be completely knocked out of operation on the initial attacks.

To allow for re-attack of generating stations which continue to provide some power and to allow for vicissitudes of weather, an additional provision for attacking half the targets a second time might be called for.

Under these circumstances, the weight of attack required to provide ninety percent probability of successful destruction of each target contributing to two-thirds of Germany's electric power capaci ty, by normally successful daylight precision bombing, may be taken as:

23,140 tons	7,020 sorties
11,570 tons	3,510 sorties
34,710 tons	10,530 sorties

Another method of computing the force required is somewhat more conservative and calls for higher numbers of sorties. Attacking generating stations in missions of 4 task forces of 2 wings each (108 bombers) against groups of 4 targets gives a 95 percent probability of destroying at least 3 targets on each mission, which may be accepted as practical certainty. Sixty-five targets would take 22 missions, totaling 9,504 sorties and 31,363 tons of bombs. Allowance for weather would raise this to 14,250 sorties and 47,844 tons of bombs, to achieve 95 percent probability of success against all of the 65 targets, with a 50 percent cushion for weather.

The task of knocking out the electric power system actually was much less difficult than that of knocking out the synthetic oil production -- and keeping it out.

This tonnage (about 35,000 to 48,000 tons) is a small portion of the total effort available in March, April, and May of 1944. During the period March-May 1944, the U.S. Strategic Air Forces flew over 60,000 sorties and dropped 198,000 tons of bombs, of which only 6,080 tons were on oil targets. Thirty-five thousand tons (or 48,000 tons) is a small portion of this effort. Obviously this is not the problem. In comparison with the total sorties (over 50,000) and tonnage of bombs actually dropped (150,000) by these air forces after Big Week in the time period before May 15, these numbers of sorties (21 or 28 percent) and tonnage (23.3 or 32 percent) of bombs for electric power is small. After May 15, the entire effort of the strategic air forces should properly have been directed to close preparation for the invasion itself. The total tonnage dropped by U.S. air forces on all targets in May was 96,464 tons. Half of this would be 48,232 tons, more than enough to have paralyzed German electric power. The RAF dropped 51,000 tons in May. The combined total from both air forces in the last half of May was 74,000 tons, which should have been ample to disrupt the French railroads.

5. Were there enough days of visual bombing opportunity to have accommodated the precision attacks against electric power targets prior to the invasion?

Some guidance can be obtained by consideration of the number of days in the spring of 1943 on which the Eighth Air Force was launched against targets in which visual bombing conditions were predicted.

In the three months, March through May 1943, there were 25 such missions, 19 of them between 1 March and 15 May. In 1944 about 150,000 tons of bombs were dropped in this time period.

It might be expected that in the corresponding two and a half months of 1944 a similar number of daylight missions had been possible.

Oil targets would have absorbed 4 of those days and 6,000 tons of

bombs, leaving 15 visual bombing days and 144,000 tons for targets other than oil. However, the winter of 1944 was especially severe, there was an unusual amount of overcast, weather forecasts were unreliable, and weather distribution was seldom in the pattern desired. To take care of the vicissitudes of weather, allowance has been made for diversion of one half of the sorties away from the primary targets to secondary targets. This would require re-attack of half of the targets.

To repeat, it is most unlikely that the weather would have have been so accommodating as to arrange for clear skies at the places desired. But this allowance for inaccurate weather forecasting and for unfavorable weather distribution provides a cushion that is ultra conservative. The bombing effort could have accounted for the destruction of two-thirds of Germany's electric power capacity in two and a half months even in the face of unusually bad weather.

The rate of repeat attacks for German electric power targets is quite a different matter from that for synthetic oil plants. The latter can be repaired by men with cutting torches, reinforcing plates, and welding tools. But the boilers that have been wrecked or the large steam turbines, or the electric generators, or the high voltage transformers and switches do not lend themselves to such treatment -- and there were no spares or reserves. A power plant or switching station that is really heavily damaged is out of commission for a long time.

If rail transportation in Germany had been established as a secondary and alternate target system, a very large tonnage could still have been directed that way. The missions which found the electric power targets obscured could have been employed against transportation. Marshaling yards are sufficiently large to warrant attack in poor visibility, or even by electronic bombing techniques. To be sure, the large 1100-pound bombs with delay fuses would not have been of optimum size for marshaling yards, but they would nevertheless have been effective.

To utilize the available tonnage against electric power targets in Germany it might have been necessary to shuttle strategic operations

from the Fifteenth Air Force in Italy to bases of the Eighth Air Force in England-an operation similar to that employed earlier by the Eighth in operations in the Mediterranean.

The tonnage actually dropped exclusive of the oil targets between 1 March and 15 May was adequate to have destroyed the German electric power system before the invasion, and still have left 15 days in May for attack of transportation in France to the extent of 48,000 tons of direct attack on the railroads.

This takes no account of the bombing of RAF Bomber Command, which contributed heavily to the "transportation plan" in France.

General Eisenhower was reported to have been exceedingly pleased with the results of the 48,500 tons of bombs delivered by all the Allied air forces against French rail transportation before the invasion. This had risen to 84,000 tons by the end of June.

These analyses are based on the assumption that the grand strategy had proceeded exactly as it actually did evolve. If, however, the offensive operations in Italy had been reduced to probing actions and the capture of Sardinia and Corsica after the surrender of Sicily, there would have been no difficulty in concentrating the efforts of the strategic air forces against their primary targets in Germany.

It appears that, even with the delay in build-up of the U.S. Strategic Air Forces, it still would have been possible to wreck the German electric power system before the invasion, without lessening the air attacks which were actually carried out on the German Air Force and the German oil industry. In this case, electric power would have had to enjoy priority over transportation in France until the middle of May 1944. Even then transportation would have absorbed a very heavy tonnage as a secondary target system of U.S. daylight operations and as a target of Bomber Command. If RAF Bomber Command had also supplemented the attacks on electric power by night attack on cities containing the largest generating capacities or the most critical switching control centers, the total effect on electric power would have been truly devastating.

There were enough fighters available by this time to provide escort for these operations.

These calculations share a common error with AWPD-1 and

AWPD-42: they presume that it is necessary to destroy two thirds of the generating capacity to cause the complete collapse of the entire system. As indicated earlier, the collapse would have been self-induced long before this number of plants had been knocked out.

Whether these operations could have been authorized and carried out before the invasion in the face of Eisenhower's vehement support of the French Rail Transportation Plan, seems highly doubtful. But they could certainly have been carried out shortly after the St. Lo breakout, using less than one-fifth of the tonnage of the U.S. Strategic Air Forces which were diverted from CBO targets, primarily to the support of the ground campaigns.

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Footnotes:

1 Haywood S. Hansell, Jr., The Air Plan that Defeated Hitler (Atlanta, Ga., 1972), pp 286-297. In some instances, author has revised the figures in this appendix.

2. USSBS German Electric Utilities subcommittee report.