WE HAVE heard much of the destruction caused by the steadily mounting weight of attack from the air by the bombing forces of the United Nations of hundreds of acres devastated in German cities, of essential war factories blasted out of production and of the coming air assault on Japan. Yet so far there has been no yardstick by which to assess more precisely the results achieved and achievable in comparison with the enemy's war effort as a whole and with the effort put into the offensive by the Allies. In the absence of even approximate figures of this nature many antagonists of bombing remain unconvinced of its value and continue to decry its effect. At the same time many advocates of the power of the strategic bombing force have few concrete facts on which to found their arguments.
Sufficient experience has now been gained with night bombing against industrial targets in Germany to assess results in terms of the destruction of enemy war effort. In fact, during the month of May (the last for which complete figures could be estimated at the time of writing), British and American heavy bombers reduced the German industrial war effort by at least 24 per cent in dropping some 15,000 British tons (16,700 U.S. tons) of bombs. In other words about four times the effort expended in bombing during the month of May would bid fair to shatter the German war machine completely.
American day bombing and British night bombing dovetail together in the most complete fashion to form the overall pattern of results each aiding the other to gain the maximum effect. The two cannot be strictly compared because, whereas the RAF has concentrated its technique on area bombing at night with bombers specially designed to carry heavy loads at a sacrifice in defensive armament, the United States Army Air Forces has specialized in the complementary daylight precision bombing from heavily defended bombers capable of fighting their way to and from the targets. This article is thus a study of the effect of British night bombing and is an attempt to analyze the results and present them in a logical form. Another, and different, method must be followed in assessing the results of the American day bombing which is such an important and steadily increasing contribution to the overall air assault on the Reich.
The truth is that both day and night bombing are essential and complementary to each other, for only by combined means can the enemy's defenses be stretched to the uttermost and the full results achieved. Night bombing is most effective against large industrial areas, day bombing against concentrated factory targets. And each contributes in its own way towards the smashing of the whole Nazi structure, like the combination of the sledge hammer and the cold chisel in razing a house.
The effect of bombing can be divided into two main aspects:
The calculations show in round figures the following results, based on present experience:
In precise terms, a 2,000-ton night raid on Germany by 800 British bombers causes damage, on an average, equivalent to the whole work of at least 77,000 Germans for one month and costs the work of 18,500 Allied men and women for the same period to achieve it. That was the approximate scale of night attack during May, 1943.
Each Lancaster in an operating life of 20 night sorties, deprives the enemy of the work of 960 men for two months. The Lancaster shows a net gain over effort represented by the work of 730 of the enemy for two months. These figures do not take into account the influence on enemy morale of continuous air attack. This effect is now becoming very great indeed and causes a serious drop in production in addition to the direct results. Nevertheless for cold mathematical analysis the moral effect may be ignored though not forgotten. Direct damage can compel the enemy to stop fighting. Lack of morale can only make that fighting less effective when the final test on land arrives.
So much for general conclusions. The data on which these estimates are based is fairly clear cut once it can be sorted out. The purpose of the rest of this article is to make these estimates clear and put them forward as a basis upon which calculations for the future can be founded always remembering the existence of the law of diminishing returns. These figures and calculations have been checked independently by authoritative sources and may be taken as conservative.
All warfare today comes down to a foundation of man-hours. Germany has an able-bodied working population, including slave labor of some 47 million men and women out of a total population of 78 million. They may be subdivided as follows:
Services . . . . . . . . . . . . . 9.5 million (20 per cent)
Direct war production . . . . . . . 7.0 million (15 per cent)
Agriculture . . . . . . . . . . . . 11.5 million (25 per cent)
Civil occupations, Transport, etc.. 19.0 million (40 per cent)
German manpower is in fact extended to the uttermost. Remove men from agriculture and the nation starves. Remove men from the civil occupations and transport fails, administration ceases, the general economic life breaks down. The number of youths arriving at the age for military service each year is insufficient to make good the losses. Therefore there is no margin left for emergency calls and the importation of slave labor can barely keep pace with vital necessities, quite apart from bombing.
When we examine this point in more detail we find that German manpower can be divided into two main groups in the face of air attack. In the first group are the services and the agricultural workers. This group of 21 million is not directly affected by bombing. The second group of war workers and the home front, amounting to 26 million, is directly influenced by bombing. On it falls the moral effect and the need to make good the damage.
A fundamental fact is that the manpower necessary to replace and repair the damage to vital installations governs the effect that bombing can have on a nation's war effort. German bombing of Great Britain in 1940 did not achieve decisive results because apart from being badly directed there was still plenty of free manpower available to deal with it. Not so in Germany today. The Reich is stretched to the limit and this stretching reflects itself in the fact that the 19 million workers in civil occupations are the very minimum needed to keep the national economic machine in the condition necessary to produce a sustained war effort, while the other 28 million produce the food, man the armed forces and turn out the weapons of war.
Thus when bombing is imposed on this strained war machine the German administration is faced with an unenviable predicament. Bombing must be met either by a reduction of the production of weapons or by a letting up in the maintenance of the civil machine. In other words, no margin has been left for contingencies doubtless relying on Goering's boast that "no foreign airplane would live to let fall a bomb on the Reich." Now, when these contingencies in fact arise, the German war machine has the choice of three evils. It must either:
The difference in effect of each of these measures is a difference only of time. The first choice affects war production immediately, the third choice affects it a little later. If, as appears to happen most frequently, the second choice is adopted then it can only postpone the crisis by mortgaging the future. It cannot avert the crash. When the crash does come it will be all the greater for the breakdown of the home front.
The meaning of all this is that the task of making good the bomb damage falls, in effect, on seven million German and foreign workers, either directly or by transfer of burden. In Germany today each workman normally does an average of 50 hours work per week for 50 weeks per year, including absence on account of sickness or other reasons. This average totals 2,500 hours of work per person per year, the real value of which, incidentally, is going down as war weariness and particularly bomb weariness overtakes the population. On this basis the seven million who are engaged directly on war production, work a total of 17,500 million man-hours per year that is, 1,460 million man-hours per month. Similarly the 19 million in essential civil industries work a total of 47,500 million man-hours per year or 3,960 million man-hours per month.
Obviously if the 1,460 million man-hours per month of direct war production are destroyed or disorganized the supply of munitions to the front will fail. Less obvious, but nevertheless true, is the fact that if a similar burden of extra essential work in the repair of damage is superimposed on the 3,960 million man-hours per month worked by the remaining 19 million, either it must be neglected at the cost of essential and certain disaster or else it must gradually absorb the efforts of the seven million at present engaged on direct war production.
The point of this is that we find that the neutralization of some 1,460 million man-hours of German labor per month whether by destruction of productive effort or by tying it up in repair work is the maximum which bombing has to achieve to stop Germany fighting. No one will doubt that in practice the end would come, through the cumulative effect of damage on working efficiency, long before this goal had been attained. A total of 500 million man-hours of destruction per month could not fail to cripple the Reich. That would be the target if the war were to be won by bombing alone.
This fact is not presented as an argument for winning the war by bombing alone as undoubtedly could be done with closely integrated day and night attack. But it does serve to show what would be needed to win the war by bombing. In reality, invasion and victory on land under cover of the air will bring the end more quickly once the enemy has been "softened-up" sufficiently by air bombardment to make land operations successful and relatively inexpensive. What then, on this basis, has Allied bombing achieved so far?
When we turn to detailed calculations of the destructive effect of night bombardment, for convenience we may examine the destruction caused by an average sortie; that is, one raid by one bomber.
First, we must establish the bomb load carried and then the area of damage which that bomb load causes. From that we can calculate first the loss of output to the enemy and then the increased work imposed on him in repairs.
On the subject of bomb load, we have concrete evidence on which to base the figures. In the RAF's first "1,000-bomber raid" on May 30, 1942 we know that 1,043 bombers dropped 1,500 (British) tons of bombs on Cologne. On this basis each bomber, of a very mixed lot, carried 1.44 British (1.61 U.S.) tons of bombs. Since then, with the arrival of the four-engined bomber in large numbers, bomb loads are officially stated to have doubled. We know, too, that many 8,000-pound (3.57 British ton) bombs are carried now. Hence, as a conservative figure we can estimate that the average bomb load per night sortie today is at least 2.5 British tons (5,600 pounds = 2.8 U.S. tons) making liberal allowance for the weight of flares, incendiary containers and similar equipment carried at night.
Turning to bomb damage we again have some definite facts on which to draw. At Cologne, 1,500 tons devastated 600 acres. From this we see that one sortie (2.5 British tons) would devastate one acre. The total weight of 10,000 tons of bombs dropped on Essen over a period of months is known to have devastated 4,000 acres. That gives the same figure of one acre per 2.5-ton sortie. We know also that each 4,000 pound bomb has a radius of total destruction of 35 yards; which works out at an area of destruction of 0.8 of an acre. On this basis a 2.5-ton sortie would flatten 1.12 acres. So that we may err on the conservative side in our calculations, let us take a figure of half an acre as devastated by one sortie.
Carrying the argument a stage further, industrial figures tell us that in an average factory, 150 square feet of floor space is allocated to each workman. This criterion gives us an average of 290 workmen per industrial acre. But we know that factory floor space on the average covers only one-third of the area occupied by the whole factory, including roads, canteens and non-productive areas of all sorts. That means that we should reduce the figure to 96 men per industrial acre. Let us take only 90 men per acre to be on the safe side.
Examination of target areas suggests that in night bombing, using modern precision methods, the ratio of industrial to other property destroyed is one-third industrial and two-thirds general. Therefore, for every half-acre of devastation (the result of each sortie) one-sixth of an acre of industrial property is laid waste. At an average of 90 men per industrial acre that means that each sortie affects the work of 15 men.
Thus, on these figures we can estimate that each heavy night bomber carries at least 2.5 British tons of bombs and with them devastates half an acre of the target area which will involve the knocking out of the working space of 15 men as well as causing other damage to general property. The important point to determine is what this destruction costs in manhours to the enemy.
This calculation needs some clear thinking and a good deal of research into German industrial methods. In practice, what happens is that the 15 men whose working space has been laid waste are either transferred to other factories or set to work on repairs. Meanwhile repairs to machine tools and replacement of buildings have to be undertaken. In fact we can divide the effect of the bombing into the following phases:
Study of German methods suggests that of the 15 men affected in the factory area, eight will be re-employed elsewhere immediately and the other seven put on repairs. The equivalent period of full time diversion in this manner would appear, from observed results, to be an average of three months.
Thus we find the total works out as follows:
(a) Loss of factory output by direct damage.
Therefore, the total loss of output per sortie is 10,928 man-hours for statistical purposes, in round figures, 10,000, manhours per night sortie.
When we turn to the repair aspect, observations and building reports suggest that a figure of 50,000 man-hours per acre of buildings destroyed is certainly not too high. So on this basis we arrive at the following:
(c) Cost of repairs to factories.
In other words the net repair cost per night sortie is 3472 man-hours.
One further item remains to be computed. It is the cost of essential repairs to other property naturally no unessential repairs will be undertaken. So we have:
(d) Cost of repairs to other property (non-industrial).
In other words 20,000 man-hours of destruction is caused to the enemy for every 2.5 (British) tons of bombs dropped at night; 8,000 man-hours per ton. Cross checks by other methods and from other sources confirm these estimates as conservative for the average results of night bombing at this writing. [Early in July. ED.]
What we want to know is:
First of all, then, let us set the 20,000 man-hours of damage per sortie against the cost to the Allies per heavy night bomber sortie. Even if we reckon a casualty rate of five per cent for the bombers and all the indications are that the losses are less than this amount that means that, on an average, each bomber has an operational life of 20 raids. Incidentally it does not mean that after 20 raids any particular bomber will not return. It merely means that on each raid, however many sorties that bomber has made already, the odds are 19 to 1 in favor of its return. Those odds will not vary for any individual machine so long as the casualty rate does not increase. At present [as of July ED.] the rate is going down.
Basing our estimates on a five per cent loss the cost per sortie in man-hours may be worked out as follows:
Bomb production and transport (2.5 tons) 100 man-hours
Fuel production and transport (900 gallons) 150 man-hours
Amortization of crew (1/20 of training period for eight men) 800 man-hours
Amortization of heavy bomber (40 of production time of 70,000 man-hours) 3,500 man-hours
Servicing, repairs, etc. (Work of ground crews of 50 per sortie) 450 man-hours
Total cost per heavy night bomber sortie 5,000 man-hours
The profit and loss account then reads:
Destruction caused in Germany per heavy night bomber sortie 20,000 man-hours
Cost per sortie in achieving this destruction 5,000 man-hours
The gain per sortie is thus 15,000 man-hours a ratio of four to one in favor of the night bomber. A 2,000-ton (800 bomber) raid may be estimated as causing 16 million man-hours of damage to Germany and costing four million manhours to the Allies. In an operating life of 20 sorties in, say, two months, each heavy night bomber robs the enemy of the work of 960 men.
The results of night bombing can be set out thus:
Destruction per ton (2,240 lb.)
Destruction per sortie 20,000 man-hours
Destruction per bomber life 400,000 man-hours
Net gain per sortie 15,000 man-hours
Net gain per bomber life 300,000 man-hours
Destruction in May, 1943 (12,500 tons dropped) 100,000,000 man-hours
The total quantity of work lost to the enemy by the scale of night attack in May, 1943, 100,000,000 man-hours represents 20 per cent of the target figure of 500,000,000 man-hours per month, the destruction of which would cripple the German war machine completely. In other words so long as the May scale of attack is maintained the enemy has to lay off 480,000 men permanently from war production or essential civil industries in order to fight the enormous effects of the bomber offensive. And this is achieved with a bomber force in the air of some 40,000 men and for a loss of 2,000 men during the month. We would have suffered many times that loss figure to cause half the damage by any other means.
When we add the rapidly growing results of the American daylight offensive the figure really begins to look impressive. By precision bombing on very carefully selected targets the effects of the day raids can cause widespread repercussions.
But this is not all. The bomber force, in addition to its effect on German production at large, ties down in defensive activities a great number of fighting men and workers who would otherwise be freed to assume an aggressive role. Further, the production of fighters for defense has been greatly expanded at the expense of bombers. The air and ground crews for these fighters, the observer corps, the flak and searchlight crews, the civil defense workers, the mine sweepers and the ship repair gangs all must be counted.
Add to them the labor and materials needed to maintain them and one finds that certainly not less than two million able-bodied Germans in all are taken away from serving on the Russian front or helping in the submarine campaign all of them by the indirect results of Allied bombing.
We know, too, that the big raids have caused irreplaceable loss of housing and the problem has become so great that the enemy is having to build temporary barracks at great effort to house the workers close enough to their work. These temporary buildings burn very easily when they are hit. We know that Germany fears the bomber offensive even more than the Russian armies because Germany believes that a defensive line can be maintained in the east but can see no way of warding off the bombers.
A doubling and trebling of the weight of Allied air attack by day and by night is coming inexorably and relentlessly. American production is still only at its beginning. British production of heavy bombs outstrips the losses and is increasing. Side by side, Air Chief Marshal Sir Arthur Harris and Maj Gen Ira Eaker are forging a doubled-edged weapon which is pounding down Germany's industrial war effort and is laying the vaunted "Fortress of Europe" wide open to final mopping up by Allied land forces when all the strategic bombing will be turned to support the invading armies.
There is no other way of scoring so great a success at so small a price. Germany has taken upon herself the worst of all alternatives. She has accepted the most appalling casualties by becoming engaged in vast land campaigns on the eastern front and has thereby laid herself the more open to the effects of air bombardment in which the British and the Americans receive relatively few casualties for the maximum results. Thus there are spared to us great numbers of the best lives of the two nations. This will have disastrous results upon the enemy for generations to come.
We may expect that in the not far distant future the weight of daylight attack will rise to sorties of 1,000 bombers perhaps 25,000 US tons (22,000 British tons) per month while the night attack reaches 25,000 British tons per month that means both the Eighth Air Force and RAF Bomber Command operating 10,000 heavy bomber sorties per month 10 raids per month by day and by night by 1,000 bombers each. The area raids will be in "packets" of 1,000 flying to devastate one huge industrial area at a time, the precision raids by day in smaller "packets," each just sufficient to knock out one highly concentrated target.
The result of this will be perhaps 250 million man-hours of damage in all, allowing for the law of diminishing returns. When that happens German war production will be so far unequal to the demands upon it that the internal economy must fall into chaos. For Germany the "writing is in the air."
This column was originally published in the September, 1943, issue of Flying magazine, vol 33, no 3, pp 57, 84, 87-88, 90.
The PDF of this column includes a table, "Basic Figures," that recaps much of the information in the text.