The total length of the barrage may be taken as 280 miles over the greater part of which the depth of water is less than 50 fathoms.

To mine any belt of water effectively there should be three lines of mines at each depth of 5 fathoms (e. g., the vertical distance between lines of mines will be 30 feet). One line of mines at each depth will be referred to as a "system." Thus the complete barrage will consist of three systems.

It is not considered necessary, however, to lay mines at a greater depth than 200 feet (33 fathoms), as submarines will not willingly go below this depth.

2. The barrage is divided into three parts:

Area A, the notified area. This area has to be made dangerous from the surface to 200 feet below it.

Area B, area C, deep mines with surface vessels and aircraft patrolling.

The above areas will be considered separately.

3. Area A:

It is necessary to make this area impassable to submarines whether diving or on the surface. Three “systems” of mines will be required. If British mines are used, each system will have lines of mines at seven different depths, whereas if American mines are used, each system will only require lines of mines at two different depths. It is therefore proposed that Americal mines should be used for the area. The barrage will consist of three systems of lines each, e. g., six lines of mines in all. Suggested method of laying the mines.—(a) The northern edge of area A would be mined first in order to restrict the movements of our fleet to the southward as little as possible.

(b) The depth of area A is 56 miles which will allow of the mine field being extended in a southerly direction without a further notification to neutrals.

(c) It is of great importance, however, to absorb as little of this space as possible on each occasion of laying mines, and for this purpose three lines of spar buoys will be laid in area A, as shown on chart 2182 B.

(d) Only one line of buoys will be required for laying the first and second systems, the third system being laid to the north of the center line of buoys. The presence of three lines of buoys will confuse the enemy as to the actual position of the mines.

(e) The spar buoys will be laid at intervals of 10 miles and will be numbered so that the minelayers can ascertain where to commence laying on each occasion. (f) The operation of laying the mines might be carried out as follows: Two minelayers to proceed to No. 2 buoy and lay lines A. 1, A. 2, as shown on chart. These lines would form part of the first system. The lines A. 1 and A. 2 would be 11 miles in length, the first mine being dropped when 2 miles from No. 2 buoy.

NOTE.-The object in not laying mines until 2 miles away from the buoy is twofold: (1) It enables the buoys to be approached if it is desired to remove them later on. (2) The buoys will give no information as to the exact position of the ends of the lines of mines.

On the next occasion the mine layers would proceed well to the eastward of No. 2 buoy, then steer south until they reached the line of buoys, shape course for No. 3 buoy and lay lines A. 1, A. 2.

The second system of mines (lines A. 3, A. 4) would be laid in a similar manner but to the southward of the line of buoys.

NUMBER OF AMERICAN MINES REQUIRED.

It is assumed mines will be laid 40 yards apart.

First system Length of the line X number of line number of mines to the mile.

=(11×11) ×2×50.

4. Area B.-The barrage will consist of three systems. Each system will have a line of mines at each of the five following depths: 65 feet, 95 feet, 125 feet, 155 feet, 185 feet.

It is proposed that the mining of this area should be undertaken by the British. Each system will require 22,500 mines.

Therefore complete barrage =three systems.

=67,500 mines.

5. Area C.-It is desirable that American mines should be used for this area as the number of sinkers required is thereby reduced considerably. A decision on this point can only be arrived at when it is known what type of sinker can be used with the American mine.

If American mines are used:

NUMBERS REQUIRED.

Complete barrage=three systems=3X2 lines

=6 lines.

Number of mines in each system-length of lineXnumber of lines Xnumber of mines to the mile.

NOTE.—This number would be considerably reduced if the X attachment is used.

The copy of the above-quoted Appendix I, which was given to Admiral Mayo for the Navy Department, bore the following notation on its face: "Admiralty would be glad to learn whether Navy Department concurs in the plans as shown."

The Admiralty "History of Northern Barrage" states that "as a result of this paper, it was decided to proceed with preparations for laying a barrage on the Aberdeen-Norway line," and adds that "the date of this decision is not known."

It is important to note that at this period the British Admiralty was apparently quite in accord with the Navy Department in regard to major features of the project, but differed with respect to some of the details. Pending the return of Admiral Mayo to the United States about the middle of October, the development of the project was almost at a standstill for want of information as to British intentions, except in the matter of design and manufacture of the new mines; but the British Admiralty proceeded with the formulation of policies and plans based on the decision to lay the barrage on the Aberdeen-Norway line. These activities will be referred to in detail

later.

The location of the proposed barrage, with the proposed area which should be notified (as it was to contain surface mines as well as deep mines), together with the suggested arrangement of the mine systems, is shown in the reproduced chart (fig. 4).

CHAPTER III.

AMERICAN CONSIDERATION AND ADOPTION OF PROJECT.

Upon the return of Admiral Mayo to the United States a conference was held in the office of the Chief of Naval Operations on October 15, 1917. The following officers were present: Admiral Benson, Admiral Mayo, Rear Admiral Earle, Capt. F. H. Schofield, Capt. R. R. Belknap, Commander Fullinwider, and Commander King.

At this conference Admiral Mayo produced for consideration the above-quoted Appendix I, setting forth the British Admiralty version of the plan for the proposed barrage. There ensued a general examination and discussion of the plan; and, the consensus of opinion being favorable, the Chief of Naval Operations, Admiral Benson, after consultation with the Secretary of the Navy, then and there directed the Chief of Bureau of Ordnance to proceed with the pro-. curement of 100,000 Mark VI mines. This action, so far as the adoption of the project was concerned, was only tentative pending a careful study of the British version; but it was regarded by the Bureau of Ordnance as tantamount to a decision to carry out the project and to provide all necessary material therefor without further delay.

Following the conference, the planning section of the office of Naval Operations and representatives of the Bureau of Ordnance conferred informally as to details of the plan, and the papers in the case were then referred to the general board for consideration.

On October 17, 1917, while the barrage project was under consideration by the general board, the Chief of Naval Staff, British Admiralty, addressed the following dispatch to the Chief of Naval Operations:

It will be necessary to increase the number of lines of United States mines in each system in the North Sea barrage from two to three if there should be any difficulty in using the lower antennae of United States mines for first supplies. Could you please state an approximate date when supply of complete mines and sinkers will begin, stating at what rate the supply will be maintained?

As all British mine layers will be fully engaged in laying British portions of the barrage will you please say how many United States mine layers will be available * * * and the output of United States mines? It is estimated that each ship could make five mine-laying trips a month. As a base for United States mines and minelayers, it is proposed to use Cromarty. The question of facilities for assembling ready for use, storage, and embarkation is being investigated on the spot. It is suggested that it is desirable that United States officers should confer with ours on this question and examine proposed arrangements as to suitability for dealing with United States mines and sinkers; also to ascertain as to whether our depot system will be suitable

for application to United States mines. It is proposed that the necessary assembling and testing of United States mines and sinkers on receipt and before issue to minelayers should be dealt with by depot staffs, provided by you if possible. It is hoped that you will be able to agree with this. United States officers if sent over can report numbers required.

I should be much obliged if you would inform me as soon as possible whether you can supply sinkers for United States mines.

On October 20, on the recommendation of the general board, the Navy Department cabled Admiral Sims substantially as follows:

The department requests to be informed whether the plan for the placing of a mine barrage across the North Sea on the Aberdeen-Ekersund line has the approval of the Admiralty. It is believed that the great experience of the British naval forces in North Sea operations and their experience in naval mining during the present war puts them in the best position to decide whether the proposed scheme is practicable in construction and maintenance and whether in the opinion of the Admiralty it is the best scheme in sight for limiting the operations of enemy submarines, provided that the Straits of Dover can be efficiently closed to the passage of submarines, which, if possible, in the opinion of the department, should be done at the earliest possible date.

The following reply in substance was received on October 23 from the Admiralty:

The mine barrier has been approved by Admiralty and the Admiralty now confirms approval. The preparations are rapidly proceeding.

Admiralty's cable of 17th indicates the assistance desired from the United States of America. This scheme is considered by the Admiralty best to be carried out at a distance from the bases of the enemy. The Admiralty are working on a supplemental scheme for operation close inshore, but any such inshore operation has the defect that a passage through for submarines can eventually be cleared by the enemy. No scheme yet tried has been effective in closing the Dover Straits to submarines, but measures are being constantly improved and they are at the least always a considerable deterrent. Mining operations on an extensive scale against submarines in the Straits of Dover commence in November. Owing to the lack of effective antisubmarine mine, this has hitherto been delayed.

The general board completed its consideration of the project and submitted its report to the Secretary of the Navy on October 24, 1917. A complete copy of this report is appended, but a summary of its "conclusions" is quoted here:

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*

*

The general board is decidedly of the opinion that of the measures discussed * * the scheme of closing the North Sea offers the best chances of success-that is, to close the North Sea by the Aberdeen-Ekersund barrier approved by the British Admiralty, and to similarly close the Dover Straits.

The general board does not underestimate the practical difficulties that must be overcome in providing the necessary material and transporting, placing, and maintaining it in the face of the determined efforts of the Germans to render the barrier abortive. Further, the barrier even when placed can not be effective without an adequate patrol. The general board is, however, encouraged to give its indorsement to this plan because it has the approval of the British Admiralty; it is proposed by it as the best practicable plan to meet present war conditions; the Chief of Bureau of Ordnance stated the material, mines, anchors, moorings, etc., can be surely supplied; and the accompanying memorandum of Capt. R. R. Belknap, United States

Navy, who has been actively engaged in conducting mining operations, points the way to handling the details of transporting and planting.

It is assumed that the British Admiralty in approving this plan recognizes the vital importance of the necessary patrol-that it is clearly seen by it where the required number of vessels is to be obtained, and that the extent of the cooperation required of the United States in this regard will be communicated to the United States Navy Department.

If it is decided to proceed with the construction of the Aberdeen-Ekersund barrier, the general board recommends that the preliminaries be arranged at once, and that suitable officers of experience in mining operations be sent to England to arrange for our participation in the work.

The report of the general board was approved by the Secretary of the Navy October 29, 1917, and on the following day the northern barrage project was favorably acted upon by the President at a Cabinet meeting.

On November 1 the Chief of Naval Operations cabled the Admiralty:

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*

Department concurs in project for mine barrier Scotland to Norway and has already taken steps to fit out eight such mine planters to sail February 1. * Expect begin shipment of mines January 15. Will send officers to confer and arrange details in a few days.