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Rear Admiral Ralph Earle, Chief of the Bureau of Ordnance, to Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters

          Navy Department

          Bureau of Ordnance

              Washington, D.C.

CONFIDENTIAL                          Oct 31, 1917.

To:  Commander, U.S. Naval Forces Operating in European Waters.

Subject:  North Sea mine project.1

     1.   The Bureau begs to advise you on the following developments that have come about in connection with the proposed North Sea joint operations between the British and American navies. The project has been approved by the Navy Department with instructions to push its completion and make it a success.

     2.   This Bureau anticipating favorable action on this matter has actually begun the manufacture of 100,000 mines of the new type designated the Mark VI.2 While estimates of time of delivery of material are not always to be depended upon, the Bureau can reasonably expect to begin shipments of the mines, complete, except anchors, by January 15th, and it will be possible to maintain a flow of about 6,000 a week as long as may be necessary.

     3.   The Bureau is possibly a little behind with the anchors, however As you probably know the British have developed a very satisfactory type of anchor (sinker) and since the Bureau wished to take no chances in the design of the anchor it requested and secured the services of Lieutenant-Commander Isherwood, one of the leading mine designers of the British Navy,3 to adapt the British type of anchor to our mine. He expects to complete his design by the end of this week, that is by November 3rd. Judging from past experience in the production of new material the Bureau will be unable in all probability to secure rapid production of anchors until January 1, 1918. But assuming that we will get priority on this work, and that we can divide the manufacture of this material among at least a dozen factories, the Bureau should be able to furnish as many as will be needed.

     4.   Another point in connection with anchors is that the Bureau had expected that the British would be able to supply at least half of the number required, but the latest advices indicate that the United States are expected to furnish all the anchors as well as the mines. The Bureau is now preparing, in accordance therewith to furnish all the sinkers necessary.

     5.   The complete length of the antenna is 100 feet, but it is divided into two sections a lower one 60 feet supported by a stream line solid wooden float and an upper section if 40 feet supported by a similar float. The wear and tear on the antenna wires will be very greatly reduced by the dash pot buffers. The upper float will stand vertical in the water and therefore will be affected to the least possible extent by wave action. The antenna wire will be 1/4-inch copper rope of very considerable strength and flexibility.

6.   While the Bureau has designed the entire antenna element to give as long life as possible it is recognized that the upper float will probably carry away sooner or later, probably after three or four months in unfavorable circumstances, but the lower float which is not subjected to any considerable wave action is expected to last indefinitely and in case the upper float carries away. The upper section of wire will trail from the lower float and still be effective; the net result of which will be a reduction in the height of the antenna from 100 feet to 60 feet.

7.   The above applies to mine which are submerged 10[0] feet and where the upper float is very close to the surface. Where the mine is submerged to 200 feet or even 150 the antenna will undoubtedly stand indefinitely certainly as long as the mine.

8.   The Division of Operations is now working up the details of organization and plan for carrying the project into execution. It appears now that the commander of our Mine Force or Captain R. R. Belknap4 will go in a week or so to England to size up the situation and make all necessary preliminary arrangements for the mine planning and of the work. He will probably be accompanied by one of his mine-layer captains. Commander Murfin5 who has been in the mine division of the Bureau for some time, and who is acquainted with the new mine, will also go to England reporting to you in about a week to inspect the station at Cromarty and see what is necessary for the establishment of an adequate mine depot to handle the material end of the project. The Bureau anticipates that while some building and facilities already exist at that point, it will be necessary for us or the British to put up some large building appropriate to the purpose. The Bureau expects also that it will be necessary to provide repair supply and other facilities necessary for the maintenance pf a very considerable mine-planting force at that point.

9.   The Bureau hopes that you will be able to assist Commander Murfin in his inspection and recommendations with the services of a civil engineer.

10.  It is intended that Commander Murfin then return to the United States to make detailed report and make arrangements for the necessary materials, etc. required for the new station and that he will later return with several officers and as a paymaster to establish mine depot at Cromarty.

11.  Some 18 vessels of large size will be designated by the Chief of Naval Operations6 as mine-laying vessels and it is planned that we shall lay our share of the mines required.

(signed) Ralph Earle.       

Source Note: Cy, DNA, RG 45, Entry 517B. Identifying marks, “28-1-1” and “1/2/A/J” appear in the top right hand corner of the document.

Footnote 1: The Northern Barrage, or North Sea Mine Barrage, was a strategic plan to blockade the route U-Boats took around Scotland to reach their patrol zones in the Northern Atlantic. As early as April 1917, the Bureau of Ordnance floated the idea of mine barrages in the North and Adriatic Seas to block the movement of U-Boats. The Royal Navy found this proposal impracticable, leading to a new suggestion in May 1917 from the United States Navy Office of Operations for a mine barrage in the North Sea; the British again expressed doubt that this plan would prove effective. See: Earle to Benson, 12 June 1917. The key to ultimately convincing the British of the success of the Barrage, and thus moving the plan forward, was the development of a new firing mechanism, the K-pistol, which posed a considerable threat to submarines over a wide area, but hardly affected surface craft. Creation of the Northern Barrage was agreed to at the Allied Naval Conference of 5 September 1917. The laying of mines began in October 1917 with twelve more minelaying excursions to follow, the last of which took place in October 1918. The barrage was never completed, however, as the approaching end of the hostilities led to the cancellation of additional excursions. In total, 56,571 out of a planned 70,177 mines were laid. Friedman, Naval Weapons of World War I: 375-376.

Footnote 2: The most important mine developed by the United States in World War I, the Mark VI was conceived specifically for the North Sea Mine Barrage, On the development of the Mark VI, see Earle to William S. Benson, 18 July 1917.

Footnote 3: Harold Isherwood, R.N.V.R.

Footnote 4: Reginald R. Belknap.

Footnote 5: Orin G. Murfin.

Footnote 6: Adm. William S. Benson.

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