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Captain Nathan C. Twining, Chief of Staff, United States Naval Forces Operating in European Waters, to Secretary of the Navy Josephus Daniels


April 18, 1918.         

FROM: Force Commander,1

TO  : Secretary of the Navy (Operations)

SUBJECT: Forwarding Planning Section Memorandum.


     1.   There is forwarded herewith enclosed a copy of Memorandum No. 172 which is a Joint Estimate of the Situation as to present and future mining policy by the Planning Section of my Staff and Plans Division of the Admiralty.

     2.   The Department is of course aware that there has been in the past very extensive mining in the Heligoland Bight both by the British Admiralty and by the enemy. Mining in that locality is still carried on whenever circumstances appear to render it desirable, but it is not regarded as important as it was early in the war. There is a very large number of mines in this area and very few enemy submarines come out from Germany by this route.

     3.   The Admiralty has also directed certain mining operations in the Cattegat3 with a fair degree of success. This work was begun about the end of March and has been carried on continuously when weather permitted.

     4.   Mining has also been undertaken in the North Channel leading to the Irish Sea. It is upon this mining project that the U. S. S. BALTIMORE has been employed since her arrival in these waters.

     5.   Laying mines in Area “B” of the Northern Barrage was begun by the British about three weeks ago, but owing to unexpected and unexplained difficulties with the mines themselves the operations was suspended temporarily before one complete line had been run. Numerous mines failed to take the correct depth, a considerable number floated and there were a number of premature explosions H M. S. GAILLARDIA while accompanying a mine layer was sunk by striking a mine.

     6.   Since the British mine was supposed to be entirely safe if laid at a depth materially different from that intended, this behavior of the mines was very puzzling and disconcerting. A 35-foot sweep was made along the mines already laid, and a number of mines were picked up, although they were supposed to have been laid at a depth of 65 feet. Most of the mines that were picked up by the sweep exploded.

     7.   The Commander-in-Chief of the Grand Fleet4 was naturally very much disturbed by these unsatisfactory results of the first mine laying, and the Admiralty have felt that they could not continue laying the barrage in Area “B” until the faults in the mines had been discovered and removed. I am not aware that they have as yet discovered what the difficulty is.

     8.   With respect to Area “B”: I have from the first consistently urged that this area be made as narrow as was practicable, considering the requirements of the Grand Fleet and of commerce, and have also held that the deep mining should be carried close up to the islands of the Orkney group.

     9.   With respect to Area “C”: I have equally held from the first that this could be made effective only by supplementing the deep mine field with a surface mine field of American mines,and that the mining should be carried up to Norwegian territorial waters, but not into them.

     10.  My views with respect to Areas “B” and “C” have previously been accepted in principle by the Admiralty, and the Department has been advised to be prepared to furnish surface mines for both of these areas.

     11.  Owing to an apparent uncertainty in the Admiralty as to the further execution of the plans for the North Barrage, I caused the matter to be brought up at the Staff Meeting this morning at which I promised the following:-

(a) We to lay two single lines of surface mines over the southern portion of Area “C” – forty to the mile

(b) British to lay one “system” of deep mines over the northern portion of Area “C”


A “system” of English mines comprises five parallel lines at different depths.

(c) We to run the two above mentioned single lines in Area “C” and a single “system” entirely across Area “A” as early as practicable.


A “system” of American mines consists of mines at 80’, 160’ and 240’ depths respectively.

(d) Whether “C” or “A” is mined first is not very material, but if the mines and sinkers for Area “C” can be sent over without delay, it would be better to mine that Area first.

(e) In view if the great difficulty of efficiently patrolling so wide an Area as the present designed Area “B”, it seems necessary to surface mine a portion of it in the same manner as is proposed for Area “C”, leaving a portion without surface mines as an exit of the Grand Fleet, this exit to be as narrow as it can safely be made.

(f) Area “B” to be deep-mined as already planned, except that the mines are to be carried close up to the coast (Islands| without leaving the seven mile channel now shown on the chart.

     12.  Rear Admiral Strauss,5 Commander of the Mine Force, was present at the meeting, and he and I were at entire concurrence at all points. The Admiralty Staff did not reach a decision, owing, I believe, to their desire to consult the Commander-in-Chief, Grand Fleet before reaching final decision. I have every reason to believe, however, that they will accede to all of the above proposals with the possible exception of (e).

     13.  A proclamation notifying the mining of Area “A” and “C” will be issued at an early date by the British Government.

     14.  As soon as the proposal to lay a double row of surface mines across Area “C” is aceeded to I shall cable to the Department requesting that the necessary material be shipped.

<N. C. Twining,>   

<Chief of Staff, Acting,>

Source Note: Cy, DNA, RG 45, Entry 517B. Document reference: “CS 14763.” For a map of the North Sea Mine Barrage, see: Map of the North Sea Mine Barrage.

Footnote 1: VAdm. William S. Sims, Commander, United States Naval Forces Operating in European Waters.

Footnote 2: See, American Naval Planning Section London: 139-170.

Footnote 3: The Kattegat is the body of water between Denmark and Sweden.

Footnote 4: Admiral Sir David Beatty.

Footnote 5: RAdm. Joseph Strauss.