Protection Against Bomb and High-Angle Shell Fire
(See page 229, this issue.)
Lieutenant L. A. Kniskern (C.C.), U.S. Navy.—This article is interesting and unique in that it represents a serious effort to establish a scientific comparison between the penetrative effects of bombing and gunfire. The author goes back to the fundamental principles of penetration, at least so far as they are represented by the de Marre formula, and then proceeds to compare the penetration of armor-piercing bombs with armor-piercing shells under various conditions for each. It is on some such firm ground of mathematical analysis that the question of effectiveness of bombs should be approached. However, one is apt to be led astray by erroneous assumptions in the mathematical analysis itself, and by limiting the analysis to a field which does not give a complete picture of the problem as a whole.
Let us examine this article, then, with these two possibilities in mind. The use of the de Marre formula to find the penetration of decks by bombs is satisfactory for approximate results. However, it must be noted that this formula, as used, takes no account of the obliquity of impact. Even a bomb dropped from a high altitude can scarcely be expected to strike a deck at exactly normal impact, and an angle of obliquity as great as 15° is quite probable. This would considerably reduce the figures given for penetration of bombs. This fact of course does not alter the author’s conclusion that “the horizontal protection required against gunfire is far greater than that required against the aerial bomb”—assuming, of course, the type of bomb discussed in that paragraph.
The conclusion that “protection against even medium caliber gunfire presents a problem more difficult than protection against the aerial bomb” is also justifiable for the type of bomb discussed there. However, it should be stated that his comparison of penetration of deck armor by 16-in. and 6-in. projectiles at the same range is somewhat exaggerated. Although the flatter trajectory of the 16-in. projectile does operate to its disadvantage in deck penetration it is extremely doubtful if actual firings would show the deck penetration of the 16-in. projectile to be less than that for the 6-in.
With these two exceptions, however, the figures quoted by M. Rougeron appear to be as accurate as necessary for the purpose of his article, and give a fair comparative idea of the performance of armor-piercing bombs under different conditions. The conclusions reached in paragraphs 4 and 5 seem perfectly logical. It has long been recognized that by decreasing the diameter of a bomb, keeping its weight constant, we reduce its air resistance and at the same time decrease the area of the hole it must punch out of the plate, the total effect being a marked increase in penetrative power of the bomb. It is also obvious that the greater the altitude from which the bomb is dropped (up to an altitude where “limiting velocity” is reached) the greater will be the velocity and penetrative power of the bomb.
But what use does M. Rougeron make of these facts? His conclusion, stated in the first sentence of paragraph 10, is: “Thus we see that the more recent ships of the line, like the standard battleship of 1914 cannot resist the aircraft bomb.” This is indeed an alarming statement, and should not go unchallenged. When we analyze its true meaning, we find little cause for apprehension as to the safety of modern ships against aircraft attack. In the first place M. Rougeron is speaking only of armor-piercing bombs, of a very special type, dropped from extremely high altitudes. As one example, taken directly from figures given in his article, we find that a 550-lb. bomb with a ratio of p/a3=16 would have a diameter of only 9.8 in., an explosive charge of only 88 lbs., and would have to be dropped from an altitude of 16,450 ft. to penetrate a deck 5.0625 in. thick. The radical nature of the design of such a bomb, as well as the improbability of bombing from such an altitude should be obvious to any one familiar with bombing practice. In the second place, the figures given by the author for penetrative power are optimistic, to say the least. However, for the purpose of argument, let us concede that under the extreme conditions prescribed by M. Rougeron it is possible to produce an armor-piercing bomb which will penetrate any existing deck. Where does such a conclusion lead us?
M. Rougeron would have us think that further improvement in penetration characteristics (smaller diameter) and further increase in bombing altitudes will make possible the penetration of the best decks that could possibly be provided. He says “the problem is not susceptible of solution with the systems of protection now in use.” This further leads us to the impression that surface ships are at the mercy of armor-piercing bombs, and conversely, that armor-piercing bombs are the best weapons to employ against surface craft.
Since the author has limited his subject to horizontal armor protection in relation to bombs and projectiles, perhaps we are not justified in criticizing the scope of the article. M. Rougeron has chosen a subject, held closely to it, and covered it thoroughly. But he leaves us with an incomplete picture, apt to be misleading.
It must be remembered that there are two general types of bombs; viz., The true armor-piercing type with a very heavy case and very small amount of explosive, an example of which, in the 550-lb. size, is described above; and the high-explosive or demolition bomb, with a larger diameter, lighter case, and much greater weight of explosive charge.
Any country setting out to determine its most effective policy in bombing naval vessels has only three courses open:
- To develop armor-piercing bombs only, carrying them to the highest state of perfection by means of experiments.
- To develop demolition bombs only.
- To develop both types, more or less in competition with each other.
M. Rougeron apparently assumes the first course would be chosen. The third course would certainly be elected by a power just beginning to experiment with bombs, and would be continued till such time as one type of bomb showed definite superiority over the other. By superiority is meant greater probability of putting enemy ships out of action. If such superiority could be established for one type of bomb it would appear to be highly desirable to employ that type of bomb to the exclusion of the other type. Or it might develop that one type of bomb should be used against one type of ship, and the other type of bomb against other classes of ships, but this latter development hardly seems probable.
Now, to return to the paper under discussion, the author bases his claims for the armor-piercing bomb on a high degree of penetrative power of bombs dropped from high altitude, and a high degree of bombing accuracy at those altitudes. In the first place we must recognize that the design of a plane to carry heavy bombs to extreme altitudes is a problem with definite limitations. But even assuming it is physically possible to carry the bomb to the desired altitude, what of the accuracy? M. Rougeron estimates that the accuracy at ft. is only 2.5 times that at 20,000 ft. Even granting this figure, which seems extremely low, let us apply it. If we assume an accuracy of 30 per cent at 10,000 ft. we have an accuracy of 12 per cent at 20,000 ft. Thus we must carry eight bombs up to this extreme altitude to get one hit, even under the most optimistic assumptions. Furthermore, the accuracy of bombing is a matter of obtaining correct results on the first attempt. There is no chance to spot and try again. Gunnery, on the other hand, becomes an accurate science by virtue of the ability to apply successive corrections, or spots, until the target is hit. With this fundamental limitation on bombing accuracy it would appear necessary to take advantage of every possible method of securing the greatest number of bits (or effective bombs). In addition to Perfecting instruments and training personnel, two methods present themselves:
- To drop the bombs from the lowest possible altitude—the lower limit being set by the effective range of anti-aircraft guns.
- Drop bombs of such a nature that a “near-miss” will do as much damage as a direct hit, or more.
Both of these methods lead to the adoption of demolition bombs. First, the demolition bomb does not require excessive altitudes, as armor penetration is not the object. Second the damaging effect of high-explosive bombs bursting under water, near the ship, is apt to be very serious. It may be argued that a direct hit with a demolition bomb is not so serious as with an armor-piercing bomb of the same weight. However, the damage to upper works, control stations, communications, etc., in the former case, may be very serious and perhaps sufficiently serious to put the ship out of effective action.
In conclusion it should be emphasized that the present writer by no means concedes a victory against surface ships to attacking aircraft—whichever type of bomb be employed. There are other things to consider besides the actual protection of the ship, for example, the development of anti-aircraft batteries, the control of the air by one’s own air force, the limitations imposed by weather, the accuracy of bombing even at low altitudes, etc. It is merely intended to point out that in dealing with high-altitude bombing, the relative merits of armor-piercing and demolition bombs must be considered. Is the promise of success for the armor-piercing bomb sufficient to warrant its development to the highest possible degree, to the probable exclusion of demolition bombs? Is the danger of such development of armor-piercing bombs sufficient to warrant the increase of protective decks to keep out the most penetrative armor-piercing bomb which may be developed?
Personnel Efficiency
(See page 1469, November, 1931, Proceedings)
Lieutenant C. S. Seely, U. S. Navy.—I have read with interest Lieutenant Becker’s article on personnel efficiency concerning the scientific selection of men for the Navy. The method described has many good points, though it misses one vital point. No effort is made to determine whether or not the men selected are naturally interested in winning for America. A man may stand No. 1 in all the various tests and yet not have the “Will to Win” for America. Everyone who has ever taken part in sports will admit that education and the ability to pass intelligence tests will avail nothing if the “Will to Win” is lacking.
A good rule to follow to determine whether or not a man will give his best to America, is to find out who his ancestors are. If his forefathers settled the country and endured the hardships incident to pushing back the frontier and defending their rights here, he will consider that the country partly belongs to him by right of inheritance and will fight to the end to protect that which is rightfully his. On the other hand, the foreigner, or the son of a foreigner, may fight, then again he may think of his fatherland.
Although Lieutenant Becker makes no mention of it in his article it is a well-known fact that the method of selection he describes eliminates many men of long American ancestry, and throws the doors wide open to sons of foreigners. The latter class as a rule inhabit the great urban centers where standards of education are high; and they are trained in the art of passing “trick” examinations. The former class who come largely from the rural districts in the South and Middlewest and who have been called our contemporary ancestors, do not come in contact with “trick” examinations.
A man born in this country would be more likely to remain loyal under adverse conditions than would an immigrant. A man whose parents were born in this country would be safer to have aboard ship than a son of an immigrant, and so on. Exactly how far to go back would be hard to determine. It is my belief that no man should be eligible for enlistment in the United States Navy unless his grandparents were born in this country. If this rule were followed we would soon have a Navy composed of 100 per cent Americans, a condition that will be sorely needed in the near future due to the wave of internationalism that is sweeping the world.
Man the Books
(See page 238, this issue)
Lieutenant Commander A. S. Wotherspoon, U. S. Navy.—The keynote of Commander King’s article undoubtedly lies in this statement that the “field of reading is too vast to be covered without considerable direction.” It was this thought that led the writer a few years ago to publish in the Proceedings an article entitled “War College and Recreational Reading Courses for Officers.” The idea at the time was that in the professional field of reading there must be about sixty books that every well-informed officer should read. It was suggested that the War College could divide these books into three reading courses of about twenty books each for the grades of ensign, junior lieutenant, and senior lieutenant. These courses were to be the preliminary reading of young officers and were to serve as a stimulus for an interest in further reading. As an incentive to complete these courses it was suggested that credit for such reading be given on an officer’s Report of Fitness.
The Bureau of Navigation Bulletin (No. 166) of October 31, 1931, contains a “Bibliography for General Reading Course.” The publications to be read in this course number fifty-one—a splendid reduction from the original staggering proportions of the War College reading course. This is a marked step forward in the field of directed reading. So too is the new correspondence course of the War College which contains excellent directed professional reading material in the various assignments. Again the correspondence course in international law is a splendid practical reading course in itself. The department of English at the Naval Academy now furnishes midshipmen with a list of selected reading comprising the best of English literature.
From the foregoing it would seem as if the Navy had now taken definite steps toward directed reading for its officers. The material is there and it remains for individual ambition alone to carry the officer along the path now so clearly marked. The only question which seems to remain is, has enough been done to stimulate and catch the interest of our young officers to start them reading at an early age?
Commander King suggests a naval book-of-the-month club. This idea would seem to be practically covered by the Bureau of Navigation Lending Library. Lists of new publications of professional interest are given out to the service periodically together with a short review of each book. These books are purchased by the Bureau of Navigation and can be had by any officer with the greatest ease by simply writing a direct request for them to the librarian. The popularity of this loan library is most evident from the fact that an average of about 240 books are sent out to officers each month.
Never has the writer witnessed such conditions existing in ships’ libraries as Commander King describes. Rather they have been open at all times to officers, well kept, and up to date. Many ships’ messes subscribe to the Book-of-the-Month Club and the Literary Guild, and these books find their way eventually to the crew’s library. In many destroyers the greatest pride has been taken in their small libraries and a cheerful and constant interchange of books has taken place between ships at all times. If any criticism is to be made of these libraries it is that there is never a full set of textbooks available for officers who are studying for examinations for promotion.
While the writer cannot agree with Commander King in his criticism of ships’ libraries yet he is fully in accord with his views that officers should read more and begin their reading at an earlier age. The Navy furnishes excellent reading material. It is easily accessible and a good deal of it is now arranged as directed reading. How may the enthusiasm to read be awakened in those who are slow in starting? As the will to read is a direct measure of the interest aroused by the subject it is still believed that reading courses for younger officers could be so arranged as to catch their interest at an early age and carry them gradually into the more serious fields of literature as they mature.