Planning Section, Headquarters of Commander, United States Naval Forces Operating in European Waters, Memo Number 10
P L A N N I N G S E C T I O N.
SUBJECT:- C R U I S E R S U B M A R I N E S
S P E C I A L P R O B L E M
SITUATION:- As at present
SITUATION:- Germany has seven completed Cruiser submarines in commission. They are of the converted mercantile type; radius of action 17,000 miles at six knots. Armament, two 5.9" guns, two 25-pounders, six inboard torpedo tubes. Speed 11 1/2 knots on the surface, 8 knots submerged.
Germany is building twelve Cruiser submarines, having a speed of 16 to 18 1/2 knots on the surface, 9 to 10 knots submerged; cruising radius about 20,000 miles. Armament, two 5.9" guns, two 4.1" guns or four 4.7" guns; eight inboard torpedo tubes. The first of these vessels will probably be commissioned shortly and all should be in service by August 1919.
Estimate as to the probable employment of these vessels and the measures that should be taken in consequence.
ESTIMATE OF THE SITUATION
Our SPECIAL and IMMEDIATE NAVAL MISSION in this war is:-
“To obtain sub-surface Command of the Sea while still retaining Command of the surface of the Sea.”
The problem with which we are dealing is but a special phase of the General Anti-Submarine Problem, so that no statement of the MISSION other than the GENERAL MISSION need be made in the solution of this Problem.
ENEMY’s PROBABLE INTENTIONS
In examining the probable intentions of the Enemy, we have first of all to consider the Mission imposed upon his Naval Forces by his situation and importance. The War that the enemy is waging is a land War; he must succeed on land if he is to dictate the terms of Peace. In order to dictate the terms of peace he must break down the will of his strongest enemies, and his strongest enemies are on the Western and Italian Fronts. If he succeeds on both of these fronts he will win the war.
From the beginning of the War, the enemy has realised that the great effort of his enemies on the Western and on the Italian Fronts had to be supported by way of the sea. He has organized the support of his own forces and directed his own land strategy so that he can do without sea communications outside the Atlantic. His BASIC NAVAL MISSION has therefore been –
“To give the maximum support to his Land Forces in obtaining a successful decision on land”.
The special features of his strategic position and the relative strength of his own and enemy surface forces have caused him to conclude that he could best support his land forces by naval effort if he concentrated that effort on –
“The maximum possible sustained attack
on the sea communications of the Allies”.
There can be no question that the above Mission is the governing one of his active naval Forces to-day, and it will continue to be their governing Mission.
The Enemy Cruisers submarines now under consideration are, or will be, a part of his active naval forces and will share in the enemy’s attempt at the accomplishment of his mission, viz:-
“The maximum possible sustained attack
on the sea communications of the Allies”.
We are sufficiently familiar with the character of the Enemy to determine that he understands and practices the doctrine of concentration of effort. He has done this so long that it is now a part of his nature – a habit from which he does not avoidably depart. Offside effort is no part of his plan. We may therefore expect that the enemy cruiser submarines will reinforce to the maximum degree possible the present submarine campaign which the enemy is carrying on. We have then solely to consider what areas will be most profitable for the operation of these vessels. Success of enemy submarine operations is concerned, first, by quantity of tonnage sunk; and second, by the character of the tonnage. There are three classes of things that come over the sea to support Allied operations in France and Italy, and these are:- Food, Munitions, Men. At present the greatest need is for Food, because of the unfavourable reflex action that the scarcity of food exerts on the civil populations, thereby tending to break down the will to win. Food is now coming principally from two sources, South America and North America.
The building of the Enemy submarines of the type under discussion in itself indicates determination to operate over wider areas of the sea, and to be able to remain away from base longer than heretofore.
So far, unrestricted submarine warfare has been limited to zones declared by Germany.
On account of the general arming of merchant vessels, and the consequent difficulty that submarines will encounter in boarding merchant vessels for visit and search even in distant areas, we may be certain that Germany will:-
(1) Operate in present declared zones, or -
(2) Declare new zones, or -
(3) Make a declaration that all the High Seas are barred zones.
In other words Germany will not submit her Cruiser submarines to the practice which has now become dangerous to submarines, to visit and search, previous to the sinking of vessels. German submarine warfare to date has been limited so closely to the barred zones as to indicate a firm policy on the part of Germany to use these zones in accordance with her declaration, and not to carry the same class of warfare into unannounced zones.
The lack of tactical handiness of the submarine cruisers, especially when submerged and when submerging, will prevent the cruiser submarines from operating in crowded waters where they are liable to the sudden attack of surface craft or air craft. The Cruiser submarine will naturally avoid Convoys on the High Seas if they are accompanied by fighting vessels of greater tactical handiness or greater gun power. It will avoid shallow waters. As it is designed for operating a long time without returning to Base, it will naturally seek – other things being equal – an area of operations in which it may find an opportunity of refuge or a convenient bottoming ground. It will naturally be attracted by localities in which it may make occasional captures of vessels, may replenish its fuel and provision supplies. Since it is designed to operate for long periods at sea, it will trust more to the gun attack than to any other form of attack, as it can carry sufficient munition to attack more ships in this way than by any other method. Secondary to the gun attack will be the torpedo attack – the mine attack by Cruiser Submarines is such an unprofitable form of attack in distant areas that it can be treated as a negligible quantity, requiring no unusual precautions.
A large quantity of grain comes from South America about this time of year, so that it will be natural to suppose that for the present the operations of Cruiser submarines should be directed against South American trade as well as against South African trade, in or near the zones of the Azores and of the Cape Verde Island. When the South American trade becomes of less importance and the North American trade becomes of great importance, we may expect a shifting of the area of operations of Cruiser submarines to the Western Atlantic, as far south as the Gulf of Mexico and the Caribbean. The present situation on the American coast in the Gulf and in the Caribbean Sea is one not calculated to give great concern to Enemy operations in that region. Further, the appearance in that region of enemy submarines the enemy knows would tend to encourage the dispersal of our Naval effort with consequent loss in the general efficiency with which the War was being conducted. Political conditions at present indicate that the enemy has refrained from unnecessarily molesting trade on the American Coast in order that American public opinion would be in a more receptive mood for advances such as those recently made by the Austrian Prime Minister. By May or June of this year, the political situation should have cleared up sufficiently to enable the enemy to judge whether it is any longer profitable for him to refrain from operations in the Western Atlantic, which from a strictly Naval and Military standpoint promises to be the most profitable to him. It would appear that the trend of events will convince the enemy that he must use his maximum power to interfere with the support America is giving the Allies, without curtailing his present submarine effort near the local areas on the coasts of Great Britain, France and Italy.
COURSES OF ACTION OPEN TO US.
As the principal effort of the Enemy cruiser submarines will probably be to sink tonnage by the use of guns our principal concern should be in methods to defeat that effort.
His Cruiser Submarines are to be armed with a battery far superior to that of the average merchant ship of to-day. The only merchant vessels carrying a battery sufficient to cope with the enemy cruiser submarine are auxiliary cruisers and American transports, the latter class of vessel should when loaded with troops never be required to engage Cruiser submarines, except while escaping his attack.
These conditions compel the adoption of the Convoy and Escort system in order that a sufficient number of guns may be assembled to be an adequate reply to the gun attack of the cruiser submarine. It is doubtful if the guns and guns’ crews assigned to the average merchant ship (American merchant vessels excluded) are adequate to cope with the gun attack of an enemy submarine, unless the Convoy is more numerous than it has so far been expedient to make it. In other words, a special Ocean Escort will always be necessary to guard against the gun attack of the Cruiser submarine.
A general extension of the system of Ocean escorts to traffic in the North and South Atlanticwill probably eventually require more Ocean Escort vessels than could be made available unless battleships were used. A large number of merchant vessels of various types are now on the stocks in both England and America and will be available in increasing numbers. To meet the probable shortage of Ocean escort, and to decrease the demand for nonproductive fuel at stations where it is supplied, would require the obligation of Ocean tonnage. It is suggested that certain of these merchant vessels be given a special armament of not less than four high powered Guns with a complete trained gun’s crew for each gun, all under the command of a competent naval officer. Vessels so armed would remain in the carrying Trade and would be available for use as Ocean escorts of Convoys throughout their voyage. If the War continues for a considerable time still the tendency will be towards the coastal regrouping of commercial traffic to the end that vessels of similar speeds may be grouped in the same Convoy, so that the loss now incident to requiring fast vessels to proceed in slow convoys will be largely eliminated. This re-grouping of vessels will probably entail an increase in the number of Convoys, with consequent increased demand for Ocean escorts. Demand for increased zone escorts of Destroyers may possibly be made by the increased production of Destroyers, but more likely by the lessened activity of enemy submarines in narrow waters, should measures now underway prove successful, as torpedo attacks by Cruiser submarines in distant waters are more difficult to deal withthan the gun attack, since the type of vessel best suited to ward off torpedo attack does not exist in sufficient numbers to permit its employment in any but focal areas. Security for vessels on the High Seas against torpedo attack of Cruiser submarines must be obtained through increased precautions, rather than through escort by destroyers. If the time ever comes when we have enough Destroyers and when they have sufficient cruising radius, it will doubtless be advisable to furnish one or two destroyers to accompany each Convoy through the areas of Cruiser submarine operations in order that they may not only guard the Convoy against attack, but may convert themselves immediately upon a submarine attack into a Hunting Group, that shall thereafter pursue the submarine which made the attack to its destruction.
In considering the measures that may be taken against the enemy submarine, we conclude that:-
(a) The maximum possible effort should be made to destroy the enemy cruiser submarine when it leaves or returns to its base.
(b) That when it causes losses of sufficient gravity [in] distant areas, the system of Convoy and Ocean Escort should be put into effect in that area until the threat disappears.
(c) That when sufficient destroyers become available without undue neglect of the focal areas or without departing from the policy of hunting groups, one or two destroyers might be assigned to each important Ocean Convoy, which destroyers would convert themselves into a hunting group immediately when contact with enemy cruiser submarine was obtained.
(d) That no destroyers now operating in European Waters should be sent in distant areas at present, because of the enemy cruiser submarine threat.
(e) The Merchant ships to be armed in the future be given one, and if possible two, 5" or 6" high-powered guns.
(f) That selected merchant vessels in proportion of about one vessel in 10 should be specially armed with four 5 or 6" guns, and specially manned with full guns’ crews for each gun under the command of a competent naval officer.
(g) That the organization for placing into effect Ocean escort system in areas likely to be areas of submarine cruiser operations should be perfected at once, and that suitable dispositions of Ocean escort vessels should be made in readiness for instituting extension of the Convoy and Ocean Escort system.
(h) That merchant vessels specially armed with four or more high powered guns should also be given a special long range radio equipment.
(i) That the extension of the present system of radio warnings by means of land stations be made so as to cover the maximum possible area and thereby enable the direction of shipping at sea.
(j) To organize hunting groups of submarines based on the American coast in readiness for operation against any enemy submarines that may visit these waters.