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Rear Admiral Ralph Earle, Chief of Bureau of Ordnance to Admiral William S. Benson, Chief of Naval Operations


Bureau of Ordnance

Washington, D. C.


To:       Chief of Naval Operations.

Subject: Mine barrier.

1.   This Bureau has had underway for some time the operation of placing a submarine mine barrier in various enemy zones. This barrier to be effective only against undersea craft.

2.   Commander Cyprian Bridge commented as follows when the details were explained to him:

A mine barrier even on such an extensive scale as the one proposed by this Bureau, to reach from Scotland to Norway might be feasible.1 There is no dou reason for not attempting the planting of such a barrier except the difficulty of getting the necessary material, that is to say the necessary number of mines. When he returns to England he will discuss the question with the Admiralty and inform it of the possibility of obtaining large numbers of mines for such a project. The first question of all to be decided will be whether of not the grand strategy of war permits or requires such an undertaking. He will inform us by cable of any decision in the matter of mines.

3.   The Bureau informed him that this was a subject for settlement between the British Admiralty and our Department and that if such cable were sent, it would be to the Department.

4.   The capabilities of the Bureau as to the manufacture of such a barrier, using the new antenna mine,2 are: minimum supply of 10,000 mines a week after a start is made, which would probably take from 45 days to two months.

5.   Instructions are awaited.

Ralph Earle.

Source Note: DTS, DNA, RG 45, Entry 517B.

Footnote 1: Earle is referring to what ultimately became the North Sea Mine Barrage, or Northern Barrage. This minefield, laid easterly from the Orkney Islands to Norway, was designed to inhibit the movement of German U-boats from their bases in Germany to Atlantic shipping lanes. With the English Channel already heavily mined, German submarines had taken to sailing around Scotland in order to sail into the Atlantic, so the construction of the Northern Barrage was intended to close off this alternate route. The Royal Navy, particularly First Sea Lord Adm. Sir George Beatty, was skeptical about the value of such a plan due to its extensive logistical and manufacturing commitments. VAdm William S. Sims shared the Admiralty’s skepticism, and it was only due to a direct appeal to President Woodrow Wilson on the part of Assistant Secretary of the Navy Franklin D. Roosevelt that the project was approved by the U.S. Navy. 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. For additional information see, Josephus Daniels, The Northern Barrage and Other Mining Activities (Washington, D.C.: Government Printing Office, 1920).

Footnote 2: These new mines were the MK 6 mines. The Mk 6 mine was a 34 in (86 cm) diameter steel sphere containing a buoyancy chamber and 300 lbs of TNT.