Memorandum Number 68: FUTURE SUBMARINE WARFARE – 1923 (How America almost lost World War II before it even started) 2

In the final days of the Great War, Naval planners had seen first hand the devastation and destruction caused by the modern machines of war.

The submarine was an example of one of the most destructive. As plans were being made for the peace, decisions about the methods for maintaining that peace would have to be made. One of the grand ideas at the time was to limit the offensive powers of the world’s navies. In this rarely discussed report from 1923, the future of the American submarine force hung in the balance. One can only imagine how the world would look today if the planners had their way. The plucky little submarine fleet that survived the devastation at Pearl Harbor on December 7th may not have been available to punish the Japanese while the nation rebuilt.

These records are held in the Naval History and Heritage Command. I am grateful for their work in preserving these valuable lessons from the past.

Mister Mac










Publication Number 7


Published under the direction of The Hon. EDWIN DENBY, Secretary of the Navy





This monograph is virtually a reproduction of the formal records of the American Planning Section in London during the Great War, presented in numbered memoranda from 1 to 71, inclusive. Memoranda Nos. 21 and 67 have been omitted as being inappropriate for publication at this time.

Before December, 1917, all strategic planning for the American Navy was done by a section of the Office of Naval Operations in Washington. Admiral Suns urged the need of a Planning Section at his headquarters in London, where comprehensive and timely information was more available; not only of the activities of American Forces, but of the Allied Navies and of the enemy.

A visit to England during November, 1917, by Admiral Benson, Chief of Naval Operations, coincided with a reorganization of the British Admiralty, which included, as a result of war experience, magnification of the function of strategic planning by their War Staff. Decision was then reached to form an American Planning Section at the London headquarters of the Commander, U. S. Naval Forces Operating in European Waters, with the idea of cooperating more closely with the British and other Allied plan makers. Up to that time the naval strategy of the Allies often appeared to lack coordination and to be formulated primarily by men so burdened with pressing administrative details as to prevent them from giving due attention to broad plans. It was intended that the new arrangements should correct these defects.

The function of the Planning Section corresponded closely to that of similar units of organization in large businesses and in armies. Its work was removed from current administration, yet necessarily required constant information of the progress of events. It comprehended a broad survey of the course of the war as a whole, as well as a more detailed consideration of the important lesser aspects.

From an examination of these records of the American London Planning Section, together with its history contained in Memorandum No. 71, prepared soon after the conclusion of the war, it is evident that the influence of the Section upon the general naval campaign was constructive, comprehensive, and important.

  1. W. Knox, Captain (Retired), U. S. Navy, Officer in Charge, Office of Naval Records and Library; and Historical Section



Memorandum Number 68:




General situation: International naval situation as at present.

Required: Estimate of the situation as to future submarine warfare with relation to—

(a) National interests.

(b) World interests.


As a result of the manner in which the Central Empires have conducted submarine operations, there exists throughout the world a public sentiment favorable to the abolition of submarine warfare and the destruction of all existing vessels of this type.

It is our purpose to examine the question of a future policy in regard to submarines, both from the point of view of world interest and national interest, and to determine the attitude which the United States should adopt toward the abolition of submarine warfare.

Theoretically the submarine is a valuable weapon of war with a large field of legitimate activity. There appears no cause for its condemnation on the ground that it has been the most powerful weapon of our adversaries, or that it has been used in violation of existing international law. The same reasons might be adduced for discarding the use of guns because they have been used to project poison-gas shells and other projectiles that cause unnecessary suffering.

It is necessary then to examine the actual methods employed by the Central Empires in submarine warfare to discover how far the successful use of submarines is dependent inherently on their employment in a manner inconsistent with the conduct of civilized warfare. If it appears that their efficiency is largely dependent on their illegitimate use in disregard of the laws of humanity, in violation of neutral rights, or in derogation of a sound policy for the world at large, it is safe to assume that in any war the temptation to employ submarines in their most efficient manner may prove too strong for a belligerent threatened with defeat, and that therefore the moral and material interests of humanity would be improved by the elimination altogether of the subsurface vessel.


The weapons of the submarine are the torpedo and the gun. In order to maintain the water-tight integrity of its hull, it is essential that the submarine be protected as far as possible from gunfire. There is thus imposed upon the vessel the necessity of submerged attack against all craft possessing guns of equal or superior range. To make a successful submerged attack it is considered essential to get within ranges of 1,000 yards—preferably 300 yards. To approach within such ranges demands the utmost secrecy. Furthermore, the safety of the submarine precludes the possibility of demanding surrender at anything but a distance that would permit the most valuable prizes to escape by utilizing their superior speed. Owing to the impossibility of always determining the hostile or neutral character of a vessel by its flag or general appearance, there will frequently exist a doubt in the mind of the submarine commander, with a strong tendency to resolve the doubt in favor of aggression. Having torpedoed a vessel, there remains no means under the average conditions of providing for the surrender of the crew or its removal to a place of safety. The security of the submarine at such close quarters requires its continued submergence until the menace to its safety is removed by the sinking of the attacked vessel. Such has been the practical operation of submarine warfare.


The legitimate use of submarines may be considered to be confined to the following:

(1) Independent attack on unsupported combatant vessels of the enemy.

Comment: The submarine has an undoubted right to attack without warning an enemy man-of-war or any vessel engaged in military operations and not entitled to immunity as a hospital ship, cartel ship, etc.

It is repugnant to the standards of civilized humanity to deliberately plan warfare with the intention of giving no quarter in battle. Hence if such an attack is made and the enemy vessel surrendered, provision should be made for the safety of the lives of the prisoners either on their own vessel or in the ship’s boats if in safe waters.

A torpedo attack usually results in the sinking of a vessel. If we imagine this vessel to be a transport loaded with troops, it would be obviously impossible for the submarine to take them on board or to insure any degree of safety to those who might be successfully embarked on the high seas in the ship’s boats.

It may be argued that a similar result might follow an action between surface ships, but it is desired to point out that the rescue of the surrendered or drowning should be the normal procedure and not the exception, as would be the case in unrestricted submarine warfare.

While submarines might be built of sufficient size and equipped in a manner that would permit their operations to conform to the rules adopted for surface craft, it is certain that such vessels would be seriously handicapped by such requirements, and it is not reasonable to suppose that they would be adopted.

(2) Independent attack on combatant enemy vessels capable of rendering mutual support.

Comment: In this case attack without warning would be justifiable. Destructions might be continued until the enemy surrendered, when humanity would require that a vessel be spared to care for the surviving crews. Unless we imagine a submarine large enough to carry prize crews to take possession of surrendered vessels, it is not reasonable to suppose that any combatant vessel would be spared.

(3) Attack, in support of surface vessels, on enemy combatant forces.

Comment: This is a purely legitimate use of the submarine which, however, has had no exemplification in the present war. Great Britain has fast submarines designed to operate with the fleet, but there is no reason to suppose that they might not be diverted to other uses not so legitimate.

(4) Capture or destruction of enemy merchant vessels.

Comment: It must be expected that the merchant vessels of belligerents will arm for defense. This is an ancient right, founded on that of self-preservation and as sound in principle as the right of a citizen to keep and bear arms. Such vessels are nevertheless noncombatants and must be regarded as such, since they are denied the right of taking the offensive.

Since, however, it would be too late for a vessel to defend herself after being torpedoed by a submarine, it is necessary for her to forestall attack as soon as the intention of the submarine can be determined. Under such conditions (which must obtain in unrestricted submarine warfare) a submarine appearing in any quarter from which an attack was possible must expect resistance from the threatened vessel.

In order to make certain that a prize shall not escape attack, the submarine, if inferior in speed and gun power, must make a submerged attack with torpedoes. He is thereby precluded from—

(a) Visit and search to determine identity as well us origin and ownership of cargo.

(b) Summoning the vessel to surrender.

(c) Taking possession of the vessel.

(d) Providing for the safety of passengers or crew.

The inhuman character of this form of warfare has led to forms of reprisals on submarines, such as the use of mystery ships, that react to make the crews of submarines still more brutal, so that no attempt is made to save life, but the submarine continues its submerged attack until the merchant vessel is sunk. Instances of submarines firing on boats filled with passengers are cited and of crews deliberately drowned after being placed on the deck of the submarine.

(5) Capture or destruction of neutral merchant vessels.

Comment: Capture of neutral merchant vessels under conditions

and restrictions imposed by international law is justifiable. Destruction after capture is contrary to international law and can not be justified in any circumstances.

The right of neutral vessels to arm for self-defense dates from the days of piracy, and it can not be denied that the same right still exists to take measures for self-preservation against a belligerent who chooses to operate in defiance of international law against friend and foe alike.

If we admit the right of neutral merchant ships to arm for self-defense, the same set of conditions arise that makes it impossible for the submarine to efficiently wage war on commerce within the bounds of international law. Nor is it apparent that any change in international law could be made that would satisfy the just claims of neutrals to the free use of the high seas for their persons or their goods that would not at the same time seriously hamper the success of the submarine. The difficulty lies in the necessity of secrecy and suddenness of attack to prevent the escape of fast merchant vessels. This is obviously inconsistent with any attempt at visit and search, which in all cases would be necessary if only to establish identity.

(6) All operations of war permitted to surface vessels.

Comment: The necessity of preserving hull integrity and the limited number of guns that can be carried by a submarine restrict sharply its employment in surface operations. Such operations, while legitimate, offer but a small field of activity; illegitimate use of submarines.

The illegitimate employment of submarines by the Central Empires in the present war consisted of—

(1) Attack without warning on enemy merchant vessels.

(2) Attack without warning on neutral merchant vessels.

(3) Attack without warning on enemy hospital ships.

(4) Sinking of enemy merchant ships without visit or search.

(5) Sinking of neutral merchant vessels without visit or search.

(6) The abandonment, without regard to safety, of passengers and crews of vessels sunk.

(7) The planting of unproclaimed mine fields outside of enemy territorial waters.

Submarine operations in the present war may be considered as typical of what may be expected in future wars, when success is dependent on the result of a war on commerce.

There is high authority for the statement that prominent naval officials of at least one of the Allies are of the opinion that the unrestricted submarine warfare conducted by Germany was justifiable, and that with the exception of its more barbarous features its adoption by this ally might be expected under similar circumstances.

It is of interest to note the several phases of submarine operations in the present war as illustrating the tendency to develop maximum efficiency regardless of legal restrictions.

The first phase consisted of submarine attacks on combatant vessels. With the abandonment of the Declaration of London and the inauguration of a general blockade, there entered a second phase, a measure of retaliation, which was distinguished by the destruction without warning of enemy merchant vessels. The protests of neutrals and the fear of drawing the United States into the war induced for a time the exception of enemy passenger vessels; but, on the other hand, destruction without warning was gradually extended to apply to enemy and neutral cargo vessels alike.

It became apparent at last that the only hope of ending the war was by a food blockade of Great Britain. In this situation the Central Empires declared for unrestricted warfare and established prescribed zones that pretended to exclude all vessels from the high seas within certain areas contiguous to the territory of the Allied Powers. Any vessel whatever entering these areas was liable to destruction without warning.


Considering submarine warfare from the standpoint of national interest, let us examine the advantages and disadvantages to be derived from its use by each of the Great Powers.

Great Britain is the greatest naval power as well as the greatest mercantile power in the world. Her existence depends on control of her sea communications. In a naval war conducted by surface craft alone she can by maintaining a large margin of strength above her probable adversaries hope to maintain her position indefinitely. In a naval war involving subsurface craft no amount of naval superiority in any class of vessel can prevent the destruction of her shipping, or, as in the present war, relieve her from the menace of starvation by blockade.

The submarines of Germany almost accomplished their purpose, although the German surface fleet was but a fraction of the united strength of the United States and the Allies, and this in the face of over 4,000 special craft, as well as mines, aircraft, and every device known to science, employed against them.

In spite of the fact that Great Britain has a large flotilla of submarines and has developed a special type for use in fleet action, her naval strength would be greatly increased by the abolition of submarine warfare, and it can be confidently expected that she would favor such a policy.

France is a continental nation ranking fourth in naval strength and merchant marine. She is directly dependent on neither for existence. Except in a world war she might expect to be supplied through her neighbors. In a war with Great Britain, submarine warfare would seem to be to her advantage. She would have little to lose and much to gain. The present war has shown, however, that submarines have little success against combatant vessels, so that, as considered heretofore, important results could be gained only by unrestricted operations against merchant shipping. Aside from any question of legality or morality involved, there is in the destruction of merchant shipping an economic loss to the world that affects all nations, whether belligerent or neutral. This phase of the subject will be discussed later. In a naval war against powers other than Great Britain, there is little that France could accomplish with submarines that could not be done with surface craft.

Italy, while not an insular nation, is dependent largely on sea-borne commerce. Her Navy and merchant marine occupy fifth place among the Great Powers. Her commerce would be largely at the mercy of any enemy in the Mediterranean. During the present war her commerce was driven from the Adriatic, and in spite of the assistance of the Allies she had great difficulty in maintaining herself. With naval operations confined to surface craft she would have been much better off. In addition to the objections to submarine warfare it should be remembered that it is a highly organized and specialized form of warfare requiring technical labor for construction, and for operation expert training, great skill, and considerable endurance to insure success. These requirements are to be found in but few countries. The Germans have set a standard of efficiency for the submarine weapon that we can expect to see but rarely attained. Italy’s strength would not be relatively improved by the continuation of submarine warfare.

Germany and Austria can not expect to be in a financial condition that will permit for at least a generation to come any attempt to revive their naval strength. Considering the fate of their existing submarines, it is safe to exclude the Central Empires from present consideration. They would probably gladly agree to abolish any form of warfare in the future. Should they eventually regain their military strength there is every reason why they should never again be trusted with the submarine weapon.

Japan is an insular nation that occupies in the Pacific a position similar to that of Great Britain in the Atlantic. She stands third in naval and mercantile strength. She has a growing fleet and a rapidly increasing merchant marine. Her only potential enemy is the United States, from whom she can expect no aggression. If, unfortunately, war should come, her position would be very favorable for submarine operations against our communications with the Philippines.

On the other hand, our submarines based on the Philippines and Guam would be within striking distance of her coasts and would be a grave threat to the commerce on which her existence depends. With submarine abolished, her surface craft could probably accomplish lawfully all and more than could submarines.

Japan has but few submarines, and these of but little efficiency, which would seem to indicate that she is in agreement with this view.

Like other nations with ambitions to be powerful commercially on the sea, she has much to lose and little to gain by submarine warfare.

Small nations, with relatively large merchant fleets, such as Holland, Norway, and Sweden, have neither the military strength to withstand the invasion of a great power, nor the means to conduct an aggressive war against a small power. In either case they could expect heavy uncompensated loss from submarines.

Small nations with little or no merchant shipping of their own might selfishly benefit by submarines in a war against a maritime power. If their submarine warfare was confined to legitimate operations against combatant vessels they would be of value in repelling invasion, but it cannot be expected that they would bring about victory against a powerful nation, and in addition to the danger of their submarines being used illegally there could be no equitable means provided of granting their use to one nation and not to another.

The United States is the second naval and mercantile power in the world. Our continental coasts lie across the ocean from any formidable enemy. No foreign invasion of our continental territory is possible, nor do we contemplate aggression against any power. Nevertheless the large merchant marine that we are building may be exposed to submarine attack in any part of the world. Such an aggression by any small or irresponsible power might cause us losses both in property and national prestige out of all proportion to the size of the offending power.

In a war with Great Britain submarines would serve a purpose in preventing the blockade and bombardment of our coasts, but the same results could be accomplished by surface craft and mobile coast-defense guns.

The chief reason why the United States should not build submarines is that public opinion would never permit their use in the same manner as that of our adversaries. Their chief use would be in the destruction of enemy merchant shipping. This the national conscience would not permit, certainly not after the German manner, while our probable adversaries would likely not be controlled by any such restrictions.

With a surface fleet second to none, the United States is in a position to vindicate its policies in every part of the world. With submarines in existence no strength in surface craft can ever insure a like security.


If we reckon naval strength in terms of dreadnoughts and battle cruisers, and exclude Russia and the Central Powers, we observe that the naval strength of the Great Powers follows closely the strength of their merchant marine and is not dependent on submarines.

Naval strength. Capital ships. Merchant tonnage (approximate). Submarines.
1. Great Britain 43 15,000,000 168
2. United States 17 5,000,000 108
3. Japan 9 1,700,000 19
4. France 7 1,500,000 55
5. Italy 5 1,000,000 6

Small powers with negligible navies are—

Merchant tonnage.
Norway 1,300,000
Holland 800,000
Sweden 700,000

We conclude that the abolition of submarines would not practically alter the standing in relative remaining naval strength of any of the Great Powers.


It is to the interest of the world at large that the evils of war be confined to the nations participating in it.

The economic interdependence of every part of the modem world makes it impossible for one country to suffer loss without in a measure affecting all. But the vital indispensable necessity to the welfare of the world is merchant shipping, the common carrier of the world that provides the sole means of interchange of products on which civilized existence has come to depend.

International law for the present has not progressed sufficiently far to forbid the destruction of belligerent merchant vessels under certain prescribed circumstances. It does forbid the sinking of neutrals.

We believe that the destruction of any merchant ships employed as common carriers is contrary to a sound world policy and should be forbidden.

As a result of the present war the world at large has been subjected to a loss of 13,000,000 tons of merchant shipping; 2,000,000 tons of this was the property of neutrals.

The loss of cargoes has impoverished the world and subjected many of the neutrals to hardships greater than those endured by some of the belligerents.

The tonnage sunk represents a direct economic loss falling upon the people of the world, whether belligerent or neutral.


The abolition of submarine warfare would be a great step in the reduction of armaments. In addition such a reduction would carry with it the elimination of all special types of craft that are necessary only in antisubmarine warfare.

If all distinctly antisubmarine craft were dispensed with and torpedo vessels reduced to a proportion of six destroyers for each dreadnought or battle cruiser, the following reduction could be accomplished in vessels already built:

Great Britain:
Submarines 168
Destroyers 167
Torpedo boats 96
Patrol boats 63
Sloops 12
Patrol gunboats 26
Armed whalers 19
Motor launches 540
Submarine depot ships 13
United States:
Submarines 108
Destroyers 70
Torpedo boats 17
Submarine depot ships 3
Converted yachts (?) 53
Submarine chasers 300


Submarines 19
Destroyers 13
Torpedo boats 24
Submarine depot ships 4
Submarines 62
Destroyers 50
Torpedo boats 121
Special gunboats (?) 10
Sloops 9
Dispatch vessels 10
Submarine chasers 50
Submarines 56
Destroyers 22
Torpedo boats 65
Submarine depot ships 1
Motor launches 147


In addition to the foregoing there could be a reduction in minesweeping vessels, aircraft, repairs, and supply vessels, as well as elimination of special nets, mines, and devices used against submarines.


We recommend—

1. That an international agreement be concluded to abolish submarine warfare.

2. That to insure against violations of this agreement all sub-surface vessels of every class whatsoever now built or building be destroyed, and that none hereafter be constructed.

3. That no merchant vessel shall hereafter be destroyed by belligerent action.

4. That merchant vessels which under present rules would be subject to destruction may be sent into a neutral port and interned in the same manner as combatant vessels.





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