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Plan for Defense against a Submarine Attack in Home Waters, Submitted to Admiral William S. Benson, Chief of Naval Operations


Office of Naval Operations


6 February, 1918.

From:     A Special Board to Formulate a Plan of Defense in Home


To:       Chief of Naval Operations.

SUBJECT:      Defense against submarine attack in home waters.

Reference:         (a) Opnav letter No.   of February 1, 1918.

                       convening Board.1


     1.   Pursuant to instructions, reference (a), the Board convened at 10 a.m, Monday, 4 February, 1918, all members present except Lieutenant Commander Foy,2 who was present beginning with the afternoon session. As a result of its deliberations, the Board submits the following report:


     2.   The Germans have completed a number of cruising submarines of large radius and large capacity and these may be used on our coast, with a view to divert some of our military activity away from European waters. The constant increase of anti-submarine forces abroad may compel an enemy effort to cause such a diversion, and the comparative openness of American waters offers a good field for submarine activities. Information is indefinite as to the number of enemy submarines possibly intended for American waters; but an approximation is sufficient for discussion. The salient features of the situation are therefore taken to be as follows:


     3.   A division of 4 submarine cruisers, each armed with 6–inch guns, 36 mines, and 16 torpedoes, and capable of at least one month’s activity on our coast, may appear in American waters without warning.

     4.   Their aim will be to destroy shipping; interrupt the transport of troops and supplies to Europe; interfere with our coastwise shipping; by these means causing the recall from abroad of some of our naval force, for defense of home waters. Bombardment of coast towns may also be done, with a view to heighten popular demand for local protection and thereby embarrass the naval administration.

     5. They will employ mines, guns, torpedoes, and bombs. Their principal activities may be expected to be directed against the main shipping centres: Halifax, New York, Hampton Roads, and Florida Straits. At the same time, by activity of some kind in several localities so separated as to suggest the presence of a large force, they may expect to produce a maximum popular disturbance early in their campaign.


     6.   The general policy of the United States is to send the maximum possible force abroad, for offensive operations in the active theatre of war. This policy the Board has kept constantly in mind, to the end that there might be no weakening of it.

     7.   With regard to any force still retained or in the future to be held in American waters which might be suitable abroad, the Board has been governed by the consideration that trans-Atlantic transit, the security of which is the chief task of the naval force based on America, depends for its success upon a sufficient guard in American as well as in European waters. The force retained in American waters can not with reasonable military prudence be reduced below the minimum required for meeting the emergency here being considered. It has devolved upon this Board to determine what that minimum is; and such determination should be held to against the repeated urgings, to send all force abroad, of individuals who have not fully considered the situation as a whole. In the course of our discussions this principle had repeatedly to be adverted to and reaffirmed. Emphasis is laid upon it as the basis of any plan for defense against hostile operations near our coast.


     8.   In the event of actual submarine hostilities on this coast, first disclosed perhaps by the sinking of a steamer by a mine, what shall be the policy as to shipping? Shall it continue, with the least possible interruptions, or shall it be held in port until the enemy submarines shall have been located and destroyed? The latter course would be to surrender at once to the enemy a large measure of success in his purpose.

     9.   It is recognized that to keep on sending out shipping may involve the loss of some vessels soon after departure from our ports[;] we are not withstanding convinced that this course should be pursued. To hold vessels in port until all is clear will encourage the enemy, both near and abroad; it will help prolong his period of activity on our coast; and will demoralize and confuse our arrangements on shore far more than would the loss of one or two vessels. Abroad, the suspension of arrivals for several weeks would have an effect serious beyond calculation. On the other hand, to continue with our sailings boldly, unshaken in our general offensive policy, would hearten our own people while giving no ground to the enemy submarine. The escort with our convoys would force the submarines to take a chance for every sinking they might attempt. From the first disclosure of their presence, their accomplishing anything in our waters should become increasingly difficult, and this can only come about by our taking the strong line of action.

     10.  On this point it is therefore the decision of the Board that we should keep on sending shipping out with the least possible delay; at the same time taking all possible offensive measures to remove the danger.

     11.  The measures necessary to put into effect the foregoing policy divide under two general heads, Control of Shipping and Military Offensive.


     12.  After discussing the several questions involved successively, the Board came to the following conclusions:

Outbound Shipping.

(a)    that where mines have appeared, outbound shipping should be routed clear of them, through a swept channel;

(b)    that shipping should use swept channels as soon after the sweeping as circumstances permit;

(c)    that coastwise shipping should proceed at night and independently; (see change.)3

(d)    that ocean shipping should proceed in convoys;

(e)    that the convoys should be as large as the available escort permit;

(f)    that convoys should be preceded to the 50 fathom curve by four submarine chasers equipped with listening attachment; (see change)

(g)    that air scouts should patrol the convoy’s intended course at least out to the 50 fathom curve, from the convoy’s departure until it clears 50 fathoms or darkness comes on; (see change)

(h)    that convoys should be accompanied by an ocean escort; by an anti-submarine escort to the 50 fathom curve; and by one or more escorting submarines for lookout; (see change)

(i)    that the ocean escort should be a cruiser, or a converted merchant vessel in naval commission, armed with guns of 5-inch or larger calibre;

(j)    that the anti-submarine escort should consist of submarine chasers armed with depth bombs and guns up to 3-inch calibre; (see change)

(k)    that the anti-submarine escort for a convoy should be the number required by approved instructions in force at the time;

(l)    that the escorting submarines with a convoy should precede it, running awash, to keep lookout for enemy submarines and warn and divert the convoy before the enemy submarine can sight it; (omit – see change)

     13.  Considering a suggestion that interference with shipping would be made more difficult by sending convoys out of more ports than are so used at present, it was concluded that available escort vessels were too few, that land transportation would be disarranged, and that harbor facilities would be taxed too much beyond their normal capacity, to offer any success for such a measure. Accordingly,

(m)  the despatch of convoys should be limited to New York

     and Hampton Roads, as at present.

     14.  The foregoing applies mainly to the area between Nantucket Shoals and Cape Hatteras. Shipping out of the Gulf, including the important fuel oil supply, has not as yet been convoyed and escort force is not available to establish such a convoy service.

     15.  A division of submarines and an aviation station are located at Key West, and dependence must be placed upon these and upon local and passing traffic and the coastwise lookout service for information of hostile submarines in the vicinity; and in such event, shipping out of the Gulf of Mexico should be routed south of Cuba. (see change)

     16.  In the event of submarines operating against shipping coming from the Canal, shipping may be routed via Cape Horn; but action as to this would be too much subject to the particulars of the situation at the time for any more definite conclusion by this Board. (omit – see change)

Incoming Shipping.

     17.  In order to route incoming shipping clear of submarine dangers, it is the consensus of the Board that the best means would be return convoys. This would insure the correct receipt of an compliance with routing instructions. Not enough cruisers being available to convoy return shipping, however, there is no choice but that –

(n)  return shipping to the United States must be

     independent of convoys. (see change)

     18.  Considering the great extent of coastal waters inside the 50 fathom curve, it will be at best possible only to keep one avenue of approach to New York and one to Hampton Roads sufficiently swept for a practical degree of safety from enemy mines. Our sweeping task is lessened by the fact that only a small number of mines can be brought over by submarines. Judging by the latest experience abroad these may be planted in small groups in several widely separated locations. There being only a few mine sweepers available, they can be employed to the best advantage by searching out a route clear of mines rather than by attempting to keep several fixed routes swept clear. In searching formation sweepers can cover more ground than in a sweeping formation. The Board concludes, therefore,-

(o)  that incoming shipping should be routed into port

     through approach channels that have been found by

     searching or sweeping to be safe.

Secrecy in Routing.

     19.  To the end that vessels may be warned daily of the positions of submarines and mines and receive directions for their movements,-

(p)  return shipping to the United States should be

     controlled by radio from the United States.

     20.  To provide for the necessary secrecy of such radio control

(q)  each belligerent vessel should carry a commissioned

communication officer of her own or of United States nationality. Such officer would be in charge of codes, would decipher code messages and transmit them to the Master of the vessel, but would have no authority over nor responsibility for the vessel. He need have no seagoing experience, but must be trustworthy and of sufficient education; hence to supply these communication officers, our trained personnel need not be drawn upon.

     21.  The foregoing provision must be undertaken immediately, to be available for use when wanted; but wholly apart from its value in emergency, the Board strongly recommends its adoption as a measure that will greatly promote the safe routing of ships in the war zone and thereby reduce tonnage losses.

     22.  Until commissioned communication officers shall have been established on board belligerent vessels, as provided in paragraph (q) above, other means to facilitate communication with incoming ships are recommended to be established, consisting of a system of secret routing for ships approaching this coast, similar to the method in use in the war zone. The Board does not consider this as an alternative, but only as a temporary means, pending the adoption of the commissioned officer system, which alone of the two has the requisite reliability and flexibility.


     23.  The foregoing measures cover the procedure necessary to carry out the policy recommended affecting shipping, namely, to continue sending it out with the least possible interruption. These measures alone constitute one means of combating enemy submarines both actively, by resisting their attacks upon convoys, and passively, by wearing out their endurance, ultimately depriving them of their main object – breaking the supply abroad. But active measures to remove the submarine from our waters are necessary in addition, lest their stay be prolonged to our disadvantage and the attendant risk to shipping continue long enough to have serious internal effect in this country.

Fixed and Local Defense.

     24.  Connected with measures of active offense the subject of purely passive defensive measures were considered. Fixed fortifications under the coast artillery should be sufficient to prevent the actual penetration of our interior waters. In addition to this, all districts have patrols at the entrance to principal harbors, and in the 2nd, 3rd, and 5th districts4 there are guns afloat in the old battle ships, MASSACHUSETTS, INDIANA, and IOWA. These means the Board considers sufficient to frustrate any attempt which might be made to enter interior waters.

     25.  Request has been made of the War Department to supplement the forces of the naval districts employed in coast defense by one or two-gun batteries at salient points along the coast which might be bombarded. While such an attack might cause no great material damage, popular clamor might compel some military dispositions seriously affecting the active theatre of operations. The War Department has replied however, that no guns can be employed for this purpose.

Submarine Nets.

     26.  Submarine nets were considered as part of fixed defenses. As to offshore nets outside New York and Hampton Roads and Long Island Sound, even if the material were available, the operation of planting them is too extensive to be undertaken within a short time; and even when in place, the nets are of small effect unless thoroughly patrolled, not to mention the effort and material required for upkeep.

(r)  The Board concludes therefore that no outside nets

should be considered, but that inside nets as maintained or planned by the Coast Artillery, and at Base Two and Cape Henry by the Navy, should be retained, and that these nets, together with fixed fortifications and harbor patrols, will afford sufficient security against any hostile attempt to enter a principal harbor.


     27.  Mines which are submerged at a depth which is dangerous to surface craft, including submarines, (subsurface mine fields) would be a greated embarrassment to our own vessels in the situation under consideration than to the enemy’s. We cannot afford to endanger or restrict the movements of our own vessels, which are at best very limited in number, and there being no hostile surface vessels involved, the Board concludes

(s)  that no subsurface mine fields should be included in

     the present plans. (see change)

     28.  At present the Mark VI mine has no attachment for safety in case of shallow planting, and the mines of earlier marks are not capable of deep planting without modification of the depth regulating apparatus. Even <with> such modification, they could not be planted at a rapid rate. These mines also have no safety provisions against shallow planting. As a whole, therefore, we have no mines suitable for deep mine fields at present. A safety attachment for the Mark VI mine is being developed, and mines of that mark are being manufactured in considerable number, so that within several months we may have a supply which could be used in emergency for deep mine fields on our own coast, though destined for another project abroad.

     29.  The free operation of our own submarines would, however, be endangered in the vicinity of deep mine fields, and hostile submarines may be expected to operate far enough off shore to be clear of any deep fields large enough to embarrass them, unless we used a number of mines beyond any possibility of supply. The chance of deep mine fields’ contributing materially to the destruction of enemy submarines is remote on account also of the small number of submarines that may be expected to operate. The board therefore concludes that

(t)  unless hostile activities on our coast be prolonged

beyond control by other measures, no deep mine fields should be planted; but

(u)  that naval districts be prepared to plant mines and

that steps be taken to make mines available for planting a deep barrier across the approaches to New York harbor and Hampton Roads. And further, (see change)

(v)  that districts should be prepared to announce

fictitious mine fields in the event of the emergency contemplated actually arising, and to route shipping accordingly.

     30.  As a whole, the passive defenses of the 1st, 2nd, 3rd, and 5th Districts are deemed sufficient for the defense of the principal harbors in those districts.

Active Offensive.

     31.  The purpose of measures of active offense is to locate and destroy the submarines.

     32.  The principal operations of these submarines must be conducted in the offing of New York, off the Capes of the Chesapeake, and in the Florida Straits and Yucatan Channel. In order to continue their operations beyond their self-contained capacity, the enemy submarines must replenish from some nearby base or by some means of supply from our coast or some neutral source.

Information Service.

     33.  To locate the submarines, we have an organized lookout service in operation along the coasts in the several naval districts and also a secret service of sufficiently wide extent and connections. These should be warned to be on the lookout for evidences of any use on our coasts and of any support to enemy submarines from on or near our coast.

     34.  The same applies to the possibility of the enemy’s use of a base in the Bahamas. Connection of our intelligence service with that of the British in the Bahama Islands should be sufficient provision to secure timely information. In this connection, it is stated by the Commander of Squadron Two, Cruiser Force,5 that a reconnaissance of the Bahama Islands shows little suitability of that region for use as a submarine base.

Air Patrol.

     35.  The naval air service, in addition to assisting the escort of the convoys, may contribute materially to the locating of submarines by air scouting off our coast, including the use of kites and dirigibles, especially between Nantucket Shoals and Cape Hatteras. It is assumed that this may and will be done, should the contemplated emergency arise.

Active Forces.

     36.  The situation has not yet sufficiently developed to enable the Board to do more than outline the offensive action that may be taken. The conclusion was reached

     (aa) that provision should now be made for forces to be

available where likely to be needed, to detect and locate enemy submarines, to act upon information of their whereabouts, and to be capable of attacking a submarine if encountered.

     37.  The kind of force that should accompany convoys has already been stated. In addition, it is the Board’s conclusion

(bb) that, in addition to harbor and inshore vessels,

there should be a force of destroyers and of submarines ready to act upon information of hostile submarines near our coast.

(cc) that the strength of these should be, in the

First Naval District,   2 destroyers,

                        1 submarine

Third Naval District,   4 destroyers,

                        5 submarines

Fifth Naval District,   4 destroyers,

                        5 submarines.

     38.  The possibility of there being more submarines capable of service, at the New London and other bases, and of more destroyers being under shake-down, after the building program shall have begun to yield more frequent deliveries, was taken into account; as also the submarines at Key West and Panama, and the vessels already in the several Districts. The forces named in paragraph (cc) above are the minimum increase needed.

Control of Active Forces.

     39.  The lookout service and reports of coastwise and other passing traffic first come under the cognizance of the naval districts, and these districts will have at disposal the forces intended to act according to the situation that may arise. The success of measures against submarines in the majority of cases will probably depend on the celerity with which forces act on information received. This indicates that their direction and control should be in the hands of the respective naval district commandants, and the Board so recommends.

Providing the Necessary Forces.

     40.  Adverting to the policy laid down in paragraph 7, the Board, examining the sources that could be drawn upon, for the force specified in paragraph (cc), concluded that the best practical plan was to utilize new destroyers and new submarines during the shake-down period, before departure for European waters.

     41.  Considering first the destroyers.- This would involve a delay at first, but this is unavoidable, if adequate provision is to be made for the contingency under consideration. Besides, the delay is not so long as at first apparent. Not less than two weeks is the probable minimum required by the average new destroyer for preliminary shake-down. To this some few days more may be needed for new fittings constantly being added, which would be installed on board on this side instead of abroad. During the time so spent the destroyer would be available for emergency if here; but if abroad she would not be operating, so no operating time is lost on this account. Further, by a somewhat longer shake-down time on our coast together with a quick run across, instead of a slow passage for shake-down en route, the ultimate date of beginning service in the war zone would be little affected. The same applies to the submarines.

     42.  The Board concluded therefore

(dd) that new destroyers should remain on our coast for one

month shake-down after commissioning, to be available for service in the event of the appearance here of hostile submarines; but that not more than nine at one time need be so detained, if prepared earlier to sail for distant service.

(ee) that the nine destroyers so detained shall be

stationed one in the 1st, and four each in the 3rd and 5th naval districts, the Commandants of which shall be instructed to use them as necessary in the event of hostile submarines appearing on this coast; otherwise not to employ them, but instead to allow them all possible freedom in their training for active service.

(ff) that to provide the necessary submarines for the

emergency service contemplated, new submarines should have a shake-down period of two months; their training course not to be interrupted but to continue in its normal course from its usual base; but, upon the appearance of hostile submarines, one division to be escorted to New York and one division to Hampton Roads; further, while based on these places, to continue their training to such extent as the situation may permit; the respective naval district commandants to observe the same attitude as towards destroyers, stated in paragraph (ee).

     43.  Still other forces are required, which, with available sources may be stated briefly,-

(gg) Participation by any force from the Atlantic Fleet,

other than the Cruiser Force as now employed in convoy duty, is not counted upon.

(hh) A force of 30 submarine chasers each, based on New

York and on Hampton Roads, will be needed for convoy escort and listening service. To provide these, the earliest deliveries intended for other districts should be diverted to the third and fifth districts until the necessary total numbers are present in these districts.

(ii) One destroyer and one submarine permanently employed

in experimentation are counted upon, with one new destroyer under paragraphs (dd) and (ee), to make up the force for the 1st Naval District.

(jj) In order to accomplish the sweeping task without

delaying shipping, in or outbound, there must be based at New York and Hampton Roads, sweepers enough to keep in service two sweeping groups of three pairs each. For this there must be 18 or more mine sweepers at each place named. As neither the 3rd District nor the 5th has this number, the Board recommends that sweepers from the 1st and 2nd Districts be added to those of the 3rd District when the occasion arises, and similarly those from the 4th District to go to the 5th District.

(kk) For the air service to be performed, it is estimated

that a force of 40 airplanes will be needed at Rockaway Inlet and at Hampton Roads in order to insure 16 planes being serviceable for escort duty; and this number should be made available. (see change)

Weakness of District Vessels.

     44.  The armament of such vessels of the naval districts as are seaworthy is too light for engaging a single submarine with success, except by surprise. It is therefore recommended

(ll) that in view of the possible appearance of submarines

armed with five-inch or six-inch (5” or 6”) guns, the armament of district vessels be replaced by larger calibres as soon as practicable, but not to the deprivation of suitable armament for vessels navigating the war zone.

Aids to Navigation.

     45.  In order to increase the navigating difficulties of submarines, especially in fog and darkness, and also to prevent the converging of shipping at a point favorable for submarines to operate, the Board recommends

(mm) that immediate steps be taken to install on board all

outside lightships on the Atlantic Coast radio and listening equipment;

(nn) and that, upon the appearance of a hostile submarine

in American waters, all submarine signal bells be stopped, the bells and whistles on outside buoys silenced, and the Nantucket Shoal lightship be withdrawn. (see change) (see additions (oo) and (pp).[)]

     46.  The Board has included in this report only such detail as has seemed necessary to make its recommendations clear, to show the extent to which existing dispositions have been taken into account, to make a decision where there has been or may be doubt or wide difference of opinion, and especially to strengthen the statement as to the minimum of increase in force necessary to retain on this side. In view of existing machinery for executing plans, it seems inadvisable to go further into details.





Rear Admiral, U. S. Navy.

     Philip Andrews

Captain, U. S. Navy.


Captain, U. S. Navy.

     L. R. De STEIGUER

Captain, U. S. Navy.

     R. R. BELKNAP

Captain, U. S. Navy.

     L. McNAMEE

Captain, U. S. Navy.

     J. R. Y. BLAKELY

Captain, U. S. Navy.


Commander, U. S. Navy.

     J. V. BABCOCK

Commander, U. S. Navy.

     E. J. FOY

   Lieut. Commander, U. S. Navy.6

Approved as changed by modifications and etc. appended.7

W. S. BENSON.                    

Source Note: Cy, DNA, RG 45, Entry 520, Box 513.

Footnote 1: This letter has not been located.

Footnote 2: Edward J. Foy.

Footnote 3: This and any following notations refer to adjustments and emendations to the original document of 6 February that were agreed to and reported on 6 March 1918.

Footnote 4: The main bases for these districts were Boston (1st Naval District), Narragansett (2nd Naval District), New York (3rd Naval District), Philadelphia (4th Naval District), and Norfolk (5th Naval District).

Footnote 5: RAdm. Harry S. Knapp.

Footnote 6: The signees to this document are: Marbury Johnston, Philip Andrews, Samuel S. Robison (“Robinson” is a typographical error), Louis R. De Steiguer, Reginald R. Belknap, Luke McNamee, John R. Y. Blakely, Simon P. Fullinwider, John V. Babcock, and Edward J. Foy.

Footnote 7: The append changes are no longer attached to this document, but, as noted above, were communicated in a later document dated 6 March 1918; See: Modifications to Plan for Defense against a Submarine Attack in Home Waters, 6 March 1918.