AMERICAN COMMITTEE OF ENGINEERS IN LONDON
CONCERNING THE COMMITTEE REPORT ON “GERMANY’S IRON INDUSTRY AND THE WAR” DEALING WITH THE PROBLEM OF AN AIR OFFENSIVE.
F.W. Lanchester, M. Inst. C.E.
In the main Report and Dossier prepared by Mr. H.A. Titcomb, which has been submitted to me, the enemy resources in coal and iron have been subjected to careful analysis; a list of iron mines is given with output of ore, so far as known, and the location and relative importance of his iron works from which he derives almost the whole of his material for munition manufacture have been analysed as to years output, relative importance, etc., and the position of every iron works of importance has been located and marked on a number of maps; in many cases photographs and large scale plans are given.
The object of the present Memorandum is to deal with the problem of dislocating his supplies by the employment to bombing aeroplanes. This Memorandum is to be regarded as a preliminary attack on the problem – an endeavour, in the first place, Part I, to lay down the objective which can be most economically made the subject of attack, that is to say, economically from the point of view of obtaining the greatest crippling effect on the enemy with bombs, etc., and, in the second place, Part II, to find a basis for the assessment of the force of aeroplanes and establishment necessary.
As the present Memorandum is intended to be in no degree final or exhaustive, arguments are put in their briefest possible form for the consideration of the Committee, and the estimate of numbers of aeroplanes, etc., may be taken as purely tentative and not based on the fullest information which may be available when actual dispositions come to be taken. The further data which will be required in order to prepare a final Report I am of opinion exist, but on such points as probable losses involved in raiding enemy country, and such further questions as the efficiency factor representing the number of machines necessary for each machine maintained in daily commission, are matters on which the Military Authorities alone can give reliable opinion, since much of the existing data is in their hands and is confidential.
The first point I will discuss is the best objective. Firstly, I agree with Mr. H.A. Titcomb that to attack the sources of the enemy’s coal supply would be far less effective than to attack the sources of his iron supply.
Since pig iron is the basis of all steel manufacture the problem, therefore, is to destroy his capacity for producing pig iron by whatever means promises the most rapid and complete success.
The two main weak points in the manufacture of pig iron, as vulnerable to the bombing aeroplane, are unquestionably:-
- Mine head works, pumping plant etc.
- Iron smelting works.
Firstly, I will say that the weight of effort should be directed against the one or the other and not against both, for if we could smash half of his iron smelting works to the extent of putting out of action half of his blast furnaces, his production of iron ore would be a matter of indifference to us – his output of pig would be reduced to one half. If, on the other hand, our effort were divided between mines and iron works, diminishing, say, the capacity of each by 25% then his capacity for producing pig iron would only be reduced in about the same ratio. In other words, once a “bottle-neck” can be made at any point in his production it pays to exert every effort of strangulation at the “bottle-neck” to restrict production still further and not to act in some other place.
Now if we attack his mines and diminish the output of ore, he can replace his loss of ore to some extent by importations from Sweden. But even if the resources of Sweden are already taxed to their limit, he has considerable stocks of ore which doubtless would enable his blast furnaces to continue for some time before our action becomes effective as diminishing his supply of pig. Beyond this the raising of ore hinges on the question of labour supply, and it is reasonable to believe that his present limit is quite as much due to labour shortage as to the number and ultimate capacity of the pits, consequently, a great many pits would have to be put out of action before his supplies would even begin to show a falling off.
On the other hand, to bomb the iron works in any vital part might, and probably would, result in the blast furnaces “freezing” and in spite of any efforts he might make there would be a stoppage for at least three or four months; also the cessation of output would be immediate.
Beyond the above, an iron works is vulnerable in so many different parts, namely – the power house, the blowing engines, the hot blast stoves or regenerators, the gas washing plant, the water cooling systems and the blast furnaces themselves, besides quantities of piping, railway track, etc. The working of an iron works is as dependent one part on another as the parts of a geared mechanism, and a bomb dropping into any of the vital parts would be as fatal as a bullet through the mechanism of an eight-day-clock.
From the point of view of difficulty or distance there is very little to choose between the main shaft works and the iron works, except that the latter are, if anything, more conspicuous and less numerous, i.e., individually more important and of a larger vulnerable area.
I conclude, therefore, that the iron works should be made the subject of the attack.
From the main Report it appears that there are four districts within raiding distance from the Western Front, the complete output of which represents 83% of the total pig iron smelted in Germany;
The approximate particulars tabulated from the Report (see Dossier p.p. 2, 38 and 40) are as follows:-
|District||Nearest Point||No. of iron works||Approx. radius in miles||Percentage of Germany’s output for 1916|
|1. Annexed Lorraine||Nancy or Verdun||22||50||30|
|4. Westphalia||Nancy or Belgium||18||200||43|
Inspections of the various plans given in the main Report reveals the fact that a large iron works commonly covers a compact site of 150 acres or thereabouts, of which the more vulnerable or dangerous portion constitutes about 10 per cent, say 15 acres. This 15 acre area can be regarded as the target and its position can be located without difficulty from the fact that it includes blast furnaces (commonly arranged in rows) and the hot blast stoves, which are no less conspicuous and which form a corresponding row or number of groups. These conspicuous landmarks are not always located within the target in the same manner, but this fact presents no difficulty, as the anatomy of each works can be studied from its plan. Plans can of course be verified by air reconnaissance and photography, and thus any extensions and alterations can be taken account of.
Within the target aforesaid, commonly representing an area of 15 acres, there are certain objectives, such as the blowing engines and power-plant houses, the gas washing plant, the pumping machinery, etc., in addition to the system of piping, which consists of some miles or more of pipes and conduits from one to ten feet in diameter, any of which, seriously damaged, will stop the whole works. Such items represent within the 15 acre danger area, or target, about ten per cent of the total or commonly 1 – ½ acres.
I shall take, for the purpose of this Memorandum, that as an average figure the accuracy of bomb-sighting will be fairly represented by assuming that all bombs would be dropped with equality of distribution within a circle of a quarter of a mile diameter, whose centre is the objective, or bulls-eye. Such a circle, viewed from 12,000 feet represents a contained angle of 6O. This does not actually mean that in bombing practice a bomb will never fall outside such a circle, but rather that the density of the “pattern” in the central portion of the circle would correspond to an equal distribution of the total number of bombs over the area stated.
The area of a circle a quarter of a mile diameter is about 32 acres And if, to be on the safe side and to allow for some of the iron works not being as large as those which the figures given in the preceding paragraph were based, we take one acre as the vital area, we reach the result that 1/232 of the total charge dropped will be effective. I have credited nothing here for the fact that beyond the vital area there is also the area, ten times as large, which I have described as dangerous. A lucky bomb on this dangerous area might easily incapacitate or destroy individual furnaces or hot blast stoves thus, crippling the output of the works to a serious extent. However, it is well to leave something in reserve to be on the safe side.
Beyond this there is hardly a point in the whole iron works at which a large bomb would not do material damage and justify itself by tearing up tracts, damaging rolling stock, wrecking roofs and so forth. The factor 1/32 therefore may be looked upon as conservative, even sufficiently so to allow for a certain demoralisation of aim due to anti-aircraft fire, etc. However, it is easy to over-estimate the effect of a bomb. A large bomb might conceivably drop even in the vital area and not actually incapacitate a single machine. It is almost inconceivable that such a thing should be possible, but it is well to allow for it. I have, therefore, taken the factor for the latter purpose of the present Memorandum as half the above, namely 1/64. On the other hand I am definitely assuming that on this reduced basis the bombing is absolutely effective and that the consequence would be those of a “freeze-up” of the blast furnaces and a stoppage, either wholly or partial, for a period of two or three months.* * Compare foot note page 7 [5 below]
To put the matter definitely, the assumption is that the bomb contents of one raiding aeroplane, which we may assume to be a single bomb of 600 or 700 lbs, or an equal weight of lesser bombs, would, if delivered to the area described as vital, put the whole works out of action for a period of two or three months, assuming the charge to take effect; and that the further assumption is that on average once in 64 times this would be the case. I do not think the fairness of this estimate can be challenged on the basis of the data given.
We may represent the above statement in a ready form by laying it down that to maintain an iron works “out of commission”, in other words, to entirely stop its output, it will be necessary to make sufficient provision to raid it at the rate of one aeroplane per diem. In practice this would of course mean that it would be raided by massed squadrons, possibly once every 2 or 3 months to the extent of fifty to a hundred machines (See note *). It would be reconnoitered and kept under air observation from time to time to ascertain whether the bombing had been effective and would be raided on a large scale as often as necessary. The basis of one machine per iron works per diem however gives, on the data, calculations and allowances aforesaid, a measure of the establishment required.
Referring back to the table given, it will be noted that in cases 1 and 2 the distances to be flown are well under a hundred miles, that is to say, two hundred miles out and home, whereas in the cases 3 and 4 the distance is twice as great. As it is not always expedient to fly on the most direct course and the point of departure (aerodrome) has to be some distance back, it would be assumed that for cases 1 and 2 two hours flying is necessary and for cases 3 and 4 that four or five hours flying is necessary. Parenthetically it may be remarked that this suggests that two types of machines will be desirable, one for the shorter distance work and one for the long distance work; also that these machines will be wanted in about equal quantity, the total number of works in the two groups being 27 and 21 respectively.
Taking first the short distance group, in which there are 27 works, we shall require 27 aeroplane journeys to be made per diem on an average, and if we take four hours flying as a day’s work we have two journeys each, or, say, 14 machines required in constant service.
Taking the second group we have 21 works, and we shall require 21 machines, since the distance will only permit of one journey per diem, the total number, therefore, of machines in constant service will require to be 35.
- Note. Actually the attack should be founded on the endeavour to bring about a “freeze-up” of the furnaces. By banking furnaces it is possible to preserve their fluidity for a fortnight or thereabouts. Hence the problem is to subject a works to repeated raids at intervals of about one week or ten days, to bring about a “freeze”, after which it may be ignored as out of action for two or three months at least.
It is for the Military Authorities, or those that have adequate experience of raiding work to state what this means in the total flying machines necessary. I am inclined myself to think that in order to maintain a daily performance the total bombing force would have to be several times as great numerically as the number required to be on duty. As a figure to form a basis of discussion I will take this factor to be five times, which will mean a total of 175 machines. This will allow an average of four days for refit and repair to each machine after a day’s work. In some cases doubtless, machines can be “gone through” and put into flying order in a few hours; in other cases the condition may be such as to require a fortnight or more in the repair shop. In taking the above factor I am assuming that each machine is provided with the usual complement of spare engines and parts and that adequate general stores are carried. If the above allowance appears more than adequate it is to be remembered that the enemy will do everything in his power to protect works which are of vital importance to his existence and to the continuing of the war, and existing experience cannot altogether be taken as a precedent; there will be a great measure of resistance which will have to be encountered and overcome.
These same considerations have equal weight, both as to loss of machines and loss of personnel. We commonly hear at present of raids being executed in which all the machines return safely; we cannot hope for anything so favourable when the work contemplated is taken seriously in hand. I am inclined, as a basis of discussion, to allow for 10% loss of machines on every raid. Since the raids contemplated on the above basis amount numerically to 48 out and home flights per diem, we must allow for five machines destroyed per diem by anti-aircraft fire and by defending fighting squadrons. This means that the manufacturing resources to support the establishment will require to supply 35 aeroplanes per week; this we may fairly assume divided in equal quantities between short and long distance machines. It will be well to allow for 20 of each type per week.
Likewise as to the loss of men either killed or taken prisoner, this would correspond with the losses of the machines and it would be necessary to provide for the training of men at the necessary rate for the special duty, namely, in the geography of the district and the character of their objectives and targets, beyond the ordinary training.
I believe that on the basis of equipment given and on the policy of execution, as above outlined, it would be possible in a very short time to so cripple the iron works in the districts in question that their output, if not reduced to zero, will become almost negligible. Also, by supporting the bombing aeroplanes by fighting squadrons and by the usual tactical jiu-jitsu in the matter of feint and surprise attacks, it would be possible to maintain a service constantly in the face of anything that the enemy could do, the raids being mainly conducted by daylight, but by no means excluding night attacks led by men who have had the necessary experience and aided by guiding lights.
It is necessary to emphasise the fact, which has already been clearly demonstrated by the main Report and is more than admitted by the writings of the German Authorities themselves, if Germany can be deprived of half of her output of pig iron the war could not last many months. (Compare Report Appendix E. page 39). I believe the statement to be in no sense exaggerated and its achievement to be within the reach of our potential resources.