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1. General Situation.
If the battle line could conduct its fire action against the enemy battle line independent of attack or threat from enemy light forces, aircraft or submarines, the O. T. C. would have a degree of freedom of action that might well be decisive. Offensive capabilities of these auxiliary forces make them dangerous threats, not only for denying freedom of action to, but also for possibility of damaging, the battle line.
How to utilize the offensive capabilities of cruisers and destroyers against an enemy battle line may, it is considered, best be studied by first examining some of the possible defensive situations or positions which may be encountered by these types prior to and during the attack. Action of cruisers and destroyers in defense of a battle line is, therefore, undertaken as a preliminary to investigation of their capabilities for offensive action against an enemy battle line.
2. Defense Against Torpedo Attack.
(a) Battle Line Defending Itself Against Surface Attack.
The ability of the battle line to defend itself against surface torpedo attack in a general daylight action is taken under investigation as a first consideration.
In order to present a set of circumstances which may be judged reasonable, it will be assumed that opposing battle lines are engaging one another with their main batteries, and that enemy destroyers ordered to attack are closing on a collision course with our battle line. For practical purposes, closing on a collision course is the quickest method by which cruisers and destroyers can reach effective torpedo range from any given point. Such a method applies either when the destroyers plan to close to the shortest practicable range, or to a predetermined position within effective range. A collision course also give, generally, the greatest rate of change of range and the least time under fire from the battle line or ships interposed.
As an initial premise, under the assumptions made above, we will consider that the attacking destroyers are taken under fire by the entire secondary battery of one broadside from all ships in the battle line. It is an optimistic premise that the secondary battery guns of all battleships will bear, or that they will all be in commission under the assumed circumstances if the enemy main battery fire control is efficient. However, effectiveness of all secondary batteries will be granted in order that the results of maximum fire on the approaching destroyers may be estimated.
A purely theoretical means for illustrating the possible results of such a situation is available in the War College rules and data, although the limitations of these generally prohibit conclusions with respect to actual conditions.
We will visualize 12 ORANGE destroyers approaching on a collision course at 30 knots to launch Type G torpedoes at 9 BLUE battleships steaming at 18 knots. It may be fair to assume that such a destroyer attack will be defeated when the destroyers are damaged 75%, or 50% if we choose. According to the War College rules, a destroyer damaged 70% from gunfire will lose all its deck tubes; damaged 50% it will lose one-half its deck tubes. An ORANGE destroyer, under the above rules, that is damaged 50% can have only from 1 ½ to 2 torpedoes that will run.
Plate 8 represents the possible results, by use of the War College scoring rules, where the entire secondary battery is employed to repulse the attack. The approximately concentric curves are the theoretical loci for different percentages of damage inflicted on the destroyers if they approach in formation from different target angles. The single elliptical curve is the theoretical locus of all points where the Type G torpedo firing range will give a 25% overrun. The diagram shows that except for approaches abaft a target angle of about 130º, and considering all practicable combinations of speeds, the entire secondary battery is unable, under War College scoring conditions, to stop one squadron of 12 destroyers in time.
As a second premise, under the same assumptions as were set forth for the case illustrated above, we will consider a case where the attacking destroyers are approaching from our van. The O. T. C. directs the leading battleship division -- which is firing on the enemy battle line -- to open fire with main battery on the destroyers. On Plate 9, it will be seen that, by using the War College scoring system, in approaches forward of target angles of 75º and 84º the main battery guns of these 3 battleships theoretically cannot damage the destroyers 50% and 75% respectively before they can fire at firing ranges that will permit the torpedoes to reach. Abaft these target angles, the main batteries, can, under the same theoretical system, defeat the attack in time. In the case illustrated, the fire of only 3 battleships against only one three-division ORANGE squadron and only one combination of speeds (18 and 30 knots) is shown. It is believed conservative to assume that, except for approaches abaft a target angle of about 80º and considering all practicable combinations of speeds, the main battery of a van division in a general action theoretically cannot stop an attack by a destroyer squadron of this size in time.
From the foregoing we may assume, certainly without actual proof, but at least for the purposes of further discussion, that the battle line guns in a general engagement cannot be relied on by themselves to stoop such a destroyer squadron attack coming in from the van "in time". If more than one destroyer squadron is approaching, the situation for the battleships is still more critical.
(b) Defense by Cruiser Against Surface Torpedo Attack.
(1) Light Cruisers defending against destroyer leaders or destroyers.
For purposes of theoretical analysis, the procedure initiated in the foregoing discussion concerning battleships will be extended into this field of investigation.
Plate 10 is diagrammatic of a battle line of 3 BLUE BBs, standing on course West at 18 knots, engaging the enemy battle line. An attacking force of 1 ORANGE CL and 12 ORANGE Oboros (DLs) approaches from any point at 30 knots on a collision course with the battle line. The curve A B C D E F represents the locus of all points having a Type G torpedo firing range with a 25% over-run. If the DLs can be stopped before they reach this curve, their attack is defeated.
The beetle-shaped "curve" N G H I J K L M O P is the locus of all points upon which interposing cruisers can be stationed and just damage the attacking force 70%, according to War College rules, by the time it reaches the curve A B C D E F, if it is brought under fire initially at about 15,000 yards.
The CL and Oboros, approaching between target angles 0º and 60º and between 120º and 180º, if they steer a collision course, can only bring their bow guns into action against the interposing cruisers. As the attacking force is assumed to use a compact squadron formation, only the CL and of the DLs can fire. The interposing cruisers are assumed to have broadside fire in all cases.
When the approach is made between target angles 60º and 120º, the attacking force can bring the broadsides of the CL and of the DLs against the interposing cruisers.
In the arc 0º to 60º, 4 Omahas are, theoretically, required to stop the attack in time; in the arc 60º to 120º, 6 Omahas; and in the arc 120º to 180º, 3 Omahas. It is seen that the arc 60º to 120º, under War College scoring rules, requires the most ships to defend; the arc 0º to 60º, fewer ships, but stationed at much greater distances from the battle line; and the arc 120º to 180º, the fewest ships and, if desired, close to the battle line.
The points N and M and H and K on Plate 10 can be connected without resulting in serious errors. This changes the "beetle" to a shape like an "apple". There will be a difference-shaped "apple" for the different types of torpedoes; for different speeds, formations and numbers of ships of the battle line; and for different kinds and speeds of attacking destroyers and different kinds of defending cruisers. If, as constants, it is assumed, for illustrative purposes, that the battle line will always be in some formation in which the battleship divisions each consist of 3 battleships in column, that the defending cruisers are Omahas, and the attacking force includes ORANGE destroyer leaders approaching at 30 knots, variables will be limited to types of torpedoes and to speeds of the battle line.
Plate 11 shows "apples" for different speeds of battle line, consisting of 3 BBs in column, where the attacking force uses Type G torpedoes. Plate 12 shows "apples" for 3 BBs in column at a constant speed of 18 knots, but with the four different types of torpedoes carried by BLUE, RED and ORANGE cruisers and destroyers. By fairing out the curves as shown on Plate 12 in dotted lines and by placing a battle line speed scale as shown, a template can be constructed which will permit laying off quickly on the mooring board the best theoretical positions for interposing Omahas to defend a battle line of any number of ships, in any standard battle formation, at any speed, and against any torpedo carried by cruises and destroyers. Such a template is shown on Plate 13. For reference it might be called an "apple card." Use of the "apple card" is explained thereon.
If the speed of the DLs in the above case varies from the constant of 30 knots, the only tangible effect on the "apple card" will be to increase or decrease the arc within which the DLs can use their broadside guns while approaching on a collision course. For any battle line speed less than one-half of the DL speed, DLs on a collision course cannot obtain broadside fire. As the battle line and DL speeds approach each other above the ration ½, the arc where the DLs can have broadside fire widens, until the two speeds are equal when the arc is 30º to 180º. Therefore, the "apple card" still applies, provided the ratio table is changed so that 6 Omahas are required, according to War College rules, to sop 13 DLs between target angles 30º to 120º. If the Dls, to obtain broadside fire, do not close on a collision course, the "apple card" and "ratio table" still hold, because the DLs must take longer to close to firing ranges, thereby giving the cruisers longer to stop them.
If the Omahas, by interposing on a station, indicated by the "apple card", can stop the attack of the Dls, the battle line may be said to have freedom of action for maneuvers, except for a turn towards the attacking Dls. In the latter case the defending cruisers probably will be too close to the battle line to stop the attack in time. In addition, if the turn leads toward the enemy battle line, the cruisers may be thrown under fire of the enemy battle line in attempting to keep the destroyers off in time. If, however, the battle line or any part, should change course towards the attacking destroyers, the defending cruisers, in order to meet attacking destroyers in time, must as a rule get out further. This is illustrated on Plate 14 and may be calculated for any similar situation by use of the mooring board and the "apple" card.
On Plate 14, a battle line of 12 BBs, originally in column, changes, by divisions column, 30º toward enemy battle line. If the interposed cruisers are on the original "apple" at a target angle of 17º, they need not change their station when the battle line changes to the new course. If they are interposed to the left of this point on the original "apple", they may gain position on the segment NML. If they should be to the right of a target angle of 17º, they must go out further from the original "apple" to the segment NIJK. If the enemy battle line is 23,000 yards from own battle line at points Q, R or S, the nearest distances cruisers may be to the points Q, R and S on the original "apple" are 14,000, 16,000 and 19,000 yards respectively. If they must go to the new "apple", these distances become 9400, 11,400 and 15,000 yards respectively -- about 45 yards nearer. When the battle line heads directly for the attacking destroyers, the cruiser at B should go to N. Distances OS and OH are equal, and are the maximum in the "apple". All other distances get smaller as the target angle increases toward the stern. In many cases, it will be found that the requirement for cruisers to go further out may not amount to so much as to prohibit the maneuver, as the cruises may have time to gain their new stations. Use of the mooring board and the "apple card" will answer the problem.
(2) Light or heavy cruisers defending against light or heavy cruisers, respectively.
Enemy CLs or CAs standing in toward our battle line may have one or all of the following tasks that are inter-related with the problems of defense against torpedo attacks: to attack our battle line with torpedoes; to clear away our cruisers which are opposed to the enemy destroyer attack; to stop our torpedo attack.
As an initial consideration for defense, it will be assumed that our cruisers, in equal to superior force to enemy cruisers standing in, will be able to defeat their torpedo attack by keeping interposed between the enemy cruisers and the head of our battle line, and at distances from our battle line on an "apple" for the type of torpedoes carried by the attacking cruisers.
This position, however, may have to be modified in order to interpose against attack by enemy destroyers on our battle line. The distance for our cruisers to go out from such an initial position will depend largely on how far out it is judged necessary to go to interpose. The attacking destroyers may often be in such position or strength as to be able to come in beyond the initial "apple" decided upon above. If, in addition, there are widely-separated attacks coming in, composed of cruisers, or destroyers, or cruisers and destroyers, the problem of defense becomes acute from the viewpoint of time and relative position.
It is the opinion of many that under such conditions, our own cruisers will have to move out beyond the "apple", noted above, particularly when an enemy destroyer attack, supported by cruisers, is [? - 2 lines of missing text] on the strength of the attack, it is possible that our own cruiser need not go beyond the "apple" more than 200 to 4000 yards. If, then, an "apple" is used that is about [? - missing text] yards beyond the [? - missing text] by enemy cruisers and destroyers, a locus is available for our cruisers opposed to such an attack. If our cruisers, in equal or superior force to enemy cruisers standing in, will keep on this locus and keep interposed between the enemy and the head of our battle line, they will, theoretically, be able to bring the enemy cruisers under sufficient fire to prevent them from reaching effective torpedo range, or from interfering with our other cruisers which are opposed to the enemy DLs or DDs.
A third consideration enters in the problem of defensive positions for our cruisers against enemy cruisers standing in to stop our destroyer attack on the enemy battle line. This will be discussed more in detail under Covering Operations in Section IV; but for the moment, it will be anticipated that if our cruisers interpose initially between enemy cruisers and our battle line, they may be in the best average position to cover our destroyer attack. From that position, the cruiser commander probably will have to decide, unless directed otherwise, which to cover -- the battle line or the destroyers. If our destroyers attack from near our battle line, our own cruises interposing between them and the enemy cruises, will, in most cases, also cover the battle line.
(c) Defense by Destroyers against Submarine Attack.
Brief analysis of possible submarine attack positions is essential in any discussion of defending the battle line against such attacks. It is assumed that destroyers, because of their design and weapons, will have the major defending role against submarines in the general action, that depth charges and ramming will be employed by them at the point of contact, and gunfire will be used from more remote positions. The problem of defense against submarine attack during a general action also entails preliminary study of how to assign sufficient numbers of destroyers to the anti-submarine screen during an approach to general action without unduly handicapping some of these destroyers in attaining positions for attacking the enemy battle line when the action is joined.
As an approximate criterion for deciding upon submarine attack positions, information available at the War College with regard to types of torpedoes and torpedo armaments will be used. According to these data, submarines of the various fleets are equipped with Type F, G or H torpedoes, general characteristics of which have been previously noted. Inasmuch as the majority of torpedoes assumedly carried by submarines are Type F or Type G, and as other types probably have the fixed or adjustable features embodied in these two, treatment of pertinent details of F and G types will suffice for the purpose at hand.
Submarines are considered able to fire no more than 4 to 8 torpedoes in a salvo. The resulting density is so thin that rarely will a submarine use any other than the torpedo's highest-speed, shortest-range setting. On Plate 15 are shown the loci of effective ranges, minus 25%, for the Type G high-speed and the Type F torpedo, when fired to hit a column of three battleships, steaming at 12 knots to 19 knots. Submarines must get within these loci in order to reach with their torpedoes with a 25% overrun.
Assuming that a submarine will submerge rather than permit itself to be sighted on the surface, a circle can be drawn with radius equal to visibility range, from the battleships, or from the anti-submarine screen, or from the light forces on the flanks or in the center, within which circle all hostile submarines will be submerged. The range, during high daylight visibility, at which a submarine on the surface can be recognized as such is, by the War College rules, 8 miles from a large or intermediate-size vessel, 7 miles from a small size light cruiser, or 6 miles from a destroyer.
A submerged submarine probably cannot make more than 10 knots to 10.5 knots submerged. In one hour this speed will run its battery down to such an extent that it will have to use a much lower speed from then on. For a submarine attempting an attack on a battle line, 7 knots submerged speed will be arbitrarily taken as a good average. With battle line speeds of advance ranging from 12 knots to 19 knots, there is a large arc of bearings from which the submarine cannot reach a firing position. The limiting bearing between the areas, where a submarine can reach firing position and where it cannot, is that target angle from which there is only one collision course. That course is at right angles to the bearing of the target from the submarine, or sin theta (target angle) equals SS speed / target speed. For a submarine speed of 7 knots and a target speed of 12, 15, 17 and 19 knots, this value of the limiting target angle is 35 ½º, 28º, 24º, and 22º respectively. If the outside and inside limits of 35 ½º and 22º are drawn tangent to the effective range loci, the diagram shown on Plate 15 will result.
From the above, it may be concluded that a submerged submarine, in order to be able to attack the target (T), which maintains a steady course north at speeds between 12 and 19 knots, must be in the acute angle between lines AD and CD. This area is about the maximum. It will be smaller as the target speed increases, and also if the submarine uses a Type F instead of a Type G torpedo. A submarine, armed with a Type G torpedo and finding itself outside this are, might use a slower speed setting on its torpedoes; thereby giving as much as about three times the effective range. However, this would not appreciably enlarge the dangerous area outside of the effective range locus, and the change of hitting would not be great, due to low density of the salvo.
If a division column of three of four battleships is taken as the unit of formation and evolution, a diagram similar to that on Plate 15 may be laid off on a mooring board to show dangerous submarine areas for any standard formation. A basic method for determining such a diagram is shown on Plate 16. By use of this method, there has been constructed, on Plate 17, a diagram for a type of cruising formation, with 10 battleships on course North, speed 19 knots, accompanied by an inner and outer anti-submarine screen.
In examining the problem of defending a battle line against submarine attack, it is evident from the foregoing, first, that the most dangerous area is in immediate proximity to the battle line, within the effective range locus of the submarine's torpedoes. Second, it may be assumed, so far as destroyers are concerned, that if there were enough destroyers arranged so that every spot inside the effective range locus were "covered" by sound detection apparatus or with anti-submarine lookouts, the submarine probably would be located. As a third consideration, it may be granted that even if the submarine is located, the submarine commander might get his shots off, with some probable sacrifice in accuracy, if he had prepared his firing data outside the effective range locus and then fired on sound, or taken one look and fired immediately, when within range.
As a first premise, however, in attempting a solution of the various factors, it may be accepted that if there are enough destroyers to locate and harass the attacking submarine within the effective range locus, the attack will be severely hampered. A second consideration then presents itself, based largely on the factor of economy of force, namely, that of providing sufficient destroyers for anti-submarine operations, and at the same time of placing them in such a position that they may be comparatively free to take, or join in, offensive operations against the enemy battle line.
Illustrative of the problem involved in the first premise, Plate 17 shows a inner an outer anti-submarine screen that probably will be effective, as far as is theoretically possible against attack by submarines equipped with Type F torpedoes, but that might be ineffective against submarines using Type G torpedoes. The only apparent remedy to ensure adequate protection within the effective range locus of Type G torpedoes is to increase the number of destroyers in the particular screen shown. Aircraft, if available, could be employed to augment this screen.
Analysis reveals many intricacies with regard to the second consideration -- that of providing a sufficient anti-submarine screen without unduly handicapping some of these destroyers in attaining positions for offensive operations against the enemy battle line. One possible solution of this problem lies in stationing destroyers near the battle line, both in the approach and in battle, except for those which may be sent to strengthen defensive cruiser operations forward of the beam.
The type of arrangement just noted provides wide possibilities in its general tactical application. Primary significance lies in the fact that ti tends to give these destroyers ease and flexibility in retaining assigned positions with reference to the battle line, because such maneuvers as reversals of course, sifts of axis, re-deployments, and changes of fleet course can be followed more easily by ships if they are near the center of movement.
Applicable to the specific problem at hand, such a general type of arrangement will provide more destroyers in the anti-submarine screen, will give the O. T. C. better control of his destroyers, and, in addition, as will be further discussed in Section IV, will place destroyers in suitable positions from which to launch attacks. An important consideration in such an arrangement is the provision of sufficient interval for freedom of maneuver, both for the destroyers concerned and for the battle line.
For purposes of further analysis of the problem, there is diagrammed on Plate 18, a four squadron anti-submarine screen in a approach disposition. The battle line is steaming at 19 knots.
On signal to deploy, the O. T. C. sends two attack squadrons to the van and 2 squadrons to the anti-submarine screen. The diagram on the fight shows the disposition ordered. Under smooth sea conditions, the two attack squadrons (I & II) can assemble ready for approach in the position shown in 25 minutes at 30 kts. This is the time for the last destroyers to join up. A good-sized attack force will be ready much sooner. The entire disposition can be competed in 45 minutes if the advanced ½ Desron III goes to its position via the unengaged side. All destroyers after the deployment are still within the effective Type G torpedo range locus for anti-submarine purposes, and the attack squadrons are in what may be tentatively considered as a good position for commencing a attack on the enemy battle line. The enemy battle line obviously may not be on a course exactly parallel to own battle line course, so that target angles may not be as shown; but with good tactics the line of bearing of the enemy battle line will be kept normal to bearing of own battle line. The target angles as shown, therefore, are probably as close as they can be anticipated. The two attack squadrons are 6000 yard ahead of the leading battleship. They can, if judged necessary, work forward as much as 18,000 yards and still be in a favorable approach area. This would take about 30 minutes longer at 30 knts. They can also be worked out toward the enemy.
If the attack squadrons are not in the anti-submarine screen during the approach, but in a position say 20,000 yards in the value (Position A), it will require them about 16 minutes longer at 30 kts to get into what has been considered here as the favorable attack position (Position B) upon the deployment shown, and much longer if a deployment on course away from the enemy is ordered. They may be driven to the other flank, which might not be desired. This is an important point. There are some approach positions for destroyers from which it is almost impracticable for them to obtain deployment stations that are at a distance from their own battle line. The time for positions A to B in plate 18 at 30 knts., with own battle line making 19 kts. is 41 minutes; to position 20,000 yds. in the van on a deployment 90º to right, is 1 hour -- an almost prohibitive time.
In the discussion above, a battle line maximum speed of 19 kts. has been assumed in order to present the most difficult conditions for destroyers. Many factors will tend to reduce the battle line speed below 19 kts. Often such a high battle line speed is not only unattainable but disadvantageous. A deliberate slowing of the battle line is sometimes advantageous to permit the re-alignment of the cruisers and destroyers both in the approach and battle. Any battle line speed below 19 knots will shorten the times given in this discussion.
Arrangement of destroyers in the most dangerous submarine area -- ie, inside the effective range locus -- is, as presented in the preceding paragraphs, a complex problem, and one that can probably be solved only for individual cases and in accordance with the numbers of destroyers immediately available.
For the dangerous area outside of the effective range locus (Plate 17), location of enemy submarines is important, in order that the battle line may be warned and have an opportunity to maneuver clear. If destroyers are not available in sufficient numbers for this purpose, aircraft or other types of surface ships suggest themselves. Effectiveness of aircraft will depend on the depth and clarity of the water, the nature of the bottom, the condition of the surface, the light effect and the altitude and relative position of the plane.
Destroyers, other surface craft, or aircraft should, for the task of location, be out far enough to give warning to the battle line in time for the O. T. C. to maneuver clear of the approaching submarine or to direct a sufficient offensive against it if maneuver is infeasible. A radius of approximately 20,000 yards, dependent somewhat on the battle line's speed, is a possible solution of this distance.
The "dangerous area" hatched on Plate 17 is useful only so long as the battle line maintains course and speed. In avoiding a submarine which has been reported in the hatched area, the battle line need turn only enough to throw the submarine out of the hatched area. In so doing, however, it may draw other submarines into a "new" hatched area. For this reason, a patrol of the nature under discussion needs to be extended beyond the hatched area shown, so as to cover locations, resulting from probable changes of battle line course, of a new area. From these elementary considerations, it is indicated that a distant anti-submarine patrol will be required almost completely around the battle line, but with attention concentrated in the current dangerous area.
(d) Defense Against Aircraft Torpedo Attack.
Aircraft torpedo attacks during the general action differ from other forms of torpedo attack by reason of the inherent ability of planes to launch the attack more quickly. Opposition to such an offensive movement by gunfire is considered somewhat more efficient than when defending by gunfire against aircraft bombing attacks in view of the fact that torpedo planes are required to fly low and on a comparatively steady course during the last portion of the approach to firing points, thus being endangered not only by a barrage effect from gunfire but also by the splash effect therefrom.
Prior to fire action between the opposing battle lines, torpedo planes may approach their target -- the battle line -- from any direction. After the main battery engagement opens, however, attack usually will be launched from some point of an arc which may be approximately defined as having limits on the battle line's engaged bow or quarter, and as extending around the unengaged side.
Aircraft naturally must launch their torpedoes, for chance of success, within the effective range locus of the type carried. If planes carry Type E, or similar, torpedoes, defensive positions against enemy attack can be outlined by constructing an "apple" in the manner shown previously on plate 16. During general action, probably only that part of he "apple" within the limits noted in the preceding paragraph will require consideration as to defense.
In the approach and engagement, it is possible that an anti-submarine screen similar to the one illustrated on Plates 17 and 18, will be efficient in defense against an aircraft torpedo attack, where the torpedo type is that believed to be carried now by aircraft. The four destroyer squadrons shown cover about 2500 yards beyond the effective range locus of assumed aircraft torpedoes, and, as arranged, they can offer gunfire opposition along the probable approach areas of torpedo planes.
In estimating how to place ships so as to have them available for defense against aircraft attacks, it is necessary, because of the high relative speed factors involved, to examine the feasibility of occupying defense positions advanced as far as possible towards the direction of probable aircraft approach. So far as defense against torpedo planes is concerned, it might be advisable to move the anti-submarine screen illustrated above, particularly that on the unengaged side, somewhat farther out than is shown, in order to bring the aircraft torpedo-carriers under fire earlier. If enemy smoke screen is laid by aircraft near effective range locus to conceal the approach, defensive destroyers in such an "advanced" position may offer opposition to smoke layers, may find themselves "outside" the screen, and certainly will be in position to pass rapidly through the screen in order to bring the torpedo planes under direct fire before the planes enter the screen. Such an "advanced" position also would tend to give an added safety factor in defending against attack from the unengaged side by enemy submarines equipped with torpedoes of more efficient characteristics than are given in War College assumptions. An anti-submarine screen such as that illustrated, will be in position to oppose torpedo plane approaches on the bow or quarter. In addition to the anti-submarine screen, cruisers or destroyers that may be occupying more advanced positions will be available to assist in decimating or defeating the threatened attack.
As in other forms of torpedo threats, early information enters as a factor, in that it will permit the O. T. C. a choice as to evasive maneuvers for the battle line.
3. Defense Against Aircraft Bombing Attack.
Primary defense of the battle line by cruisers and destroyers against aircraft bombing attacks will be considered as gunfire from positions that will result in as little fire interference as possible between own ships. Smoke has been suggested, under conditions where smoke will lie, and has been used in the fleet; but to date insufficient experience has been gained to indicate its effectiveness in defense.
Here again, as in defense against aircraft torpedo attacks, positions of available cruisers and destroyers require examination with respect to their assignment to stations at "advanced" distances from the battle line. Study has been made in the Fleet, by use of "reverse bomb-sight" curves, of the time at which maneuvers are considered necessary for avoiding bombs, that are about to be, or have been, dropped from horizontal bombers. Analysis of these curves has led many to the opinion that destroyers in the anti-submarine screen, even if equipped with sufficient anti-aircraft guns, will be too close to the battle line to afford adequate defense against high bombing attacks, but may be of some effectiveness against dive-bombers.
Cruisers and destroyers outside of positions in the general vicinity of the battle line will be of some assistance in defending against such attacks, but a more intensive fire than will be provided by them in present types of approach and battle dispositions is indicated as necessary. One attempt at a solution of this latter problem has been taken by RED, in converting small cruisers into anti-aircraft defense ships, which are apparently to accompany the battle line into general action.
4. Defense Against Enemy Mine-Laying.
Extensive discussion of defense of the battle line against enemy mine-laying activities is unnecessary. Brief note of such activities and possible defense against them is relevant, however, in view of the fact that mine-layers may accompany a fleet into action, and because of the assumption that ORANGE cruisers and destroyers and some RED cruisers are equipped to carry mines.
Gunfire against enemy ships laying mines is an obvious form of "defensive" measure; and in this, the previous discussion of time and relative position factors in the problem of interposition is applicable.
Probably more important as a measure of battle line defense, however, is the detection of mine-laying and the prompt reporting of such activities, in order that forces in the vicinity may keep clear and so that the O. T. C. may have opportunity to maneuver the battle line out of the dangerous area. This may be especially significant in the case of a turn towards or pursuit of the enemy battle line.
A third feature of defense involves consideration of the possibility of mine-sweeping by destroyers in the van. Information available indicates that RED has made some application of this feature in his later destroyers.
5. Defense Against Enemy Gas Attack.
Mention is made of the possibility that enemy cruisers and destroyers, or smaller, special types of ships, may be among those to employ either gas shell or gas screens. Decision may be necessary in detaching cruisers and destroyers from their assigned position and ordering them to destroy enemy ships of similar or smaller type that are conducting a gas shell or gas screen offensive against the battle line. As has been noted, local defense measures will include masking of personnel, maneuvers to throw off or clear such a gas attack, and decontamination. As a general gas defense measure, gunfire against enemy units employing gas probably will be the only means available to cruisers and destroyers.
6. Defense (and Offense) by Means of Smoke Screens.
Smoke may be laid by cruisers and destroyers under certain weather conditions for various defensive purposes. Among them are: to cover a disadvantageous disposition of the battle line, to mask a maneuver, to protect cruisers and destroyers in attack or when under heavy fire. The situations are numerous, and in addition they involve, either by regulation or by the nature of smoke screens, offensive possibilities, such as isolating portions of the enemy. In view of the latter circumstance, the subject of smoke screens in defense and offense will be discussed briefly in conjunction.
Characteristics of smoke screens are generally well known. They require special weather conditions to insure lying. Strong wind, low barometer, and misty or rainy weather are usually favorable. If they will lie, they can be laid down wind, up wind, and across wind, provided sufficient angle between course of layers and direction of wind is obtained to give a degree of breadth to the screen.
If one's fleet is to windward, smoke will drift towards the enemy and will cover forces to leeward. Destroyers attacking can cover themselves when approaching from windward.
If one's own fleet is to leeward, smoke will drift away from the enemy and not cover forces to windward, but it
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O.T.C.'s flagship, he would hesitate to turn toward the nearby screen for fear of what might be just beyond it. The tendency probably would be for him to move away from the screen. On the other hand, RED's range of vision is not greatly affected. The Screen A appears to him just a bank of smoke on the horizon, subtending a small azimuth arc. In view of the foregoing and the difficulty of light surface forces laying a smoke screen near the enemy, the airplane smoke curtain, which seems to have greater possibility of being laid where wanted in much quicker time, suggests itself.
Plate 20 illustrates Case [?]. In this case BLUE is between two ORANGE foces with which he is engaged. He decides to block off the direct fire of Force A with smoke while concentrating on Force B. The BLUE smoke layers at S and the BLUE battle line smoke. S keeps to leeward of, and not far from, the leader of the battle line. BLUE in this case does not care how restricted his view or his freedom of maneuver twoard Force A is. He neither wants to maneuver in that direction nor be seen from there. He only wants to be sure that he is well covered so that A cannot see him and that his smoke is well under control. A position of the BLUE smokers near the BLUE battle line seems to assure this.
The disadvantage of smoke is the danger of interfering with effective gunfire of own battle line and in covering those forces which it is disadvantageous to cover. This arises from the loss of control of the smoke once it is laid, the difficulty of anticipating how far it will go and how long it will like, and the lack of information of what the O.T.C. may plan to do with the battle line.
Smoke laid by light forces is a two-edged sword that may cut both ways. To compromise satisfactorily between its disadvantages and advantages by a single rule is difficult. Each tactical situation merits its own solution. At some times it will be advisable to keep the laying of smoke screens in the hands of the O. T. C. exclusively; at other times the light forces may have discretionary powers. Trained judgement of the officer on the spot can never be dispensed with. It probably will be a save plan for the O. T. C. to retain control of all smoke screens in areas adjacent to the battle line and to windward of it; and to grant discretion to commanders in the more remote areas with the understanding that battle line operations and plans must not be interfered with.
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