Commander Harris Laning, Commander, Officer Personnel Division of the Bureau of Navigation, to Secretary of the Navy Josephus Daniels
December 14, 1917.
From : Commander Harris Laning.
To : Secretary of the Navy (Operations)
Subject : A plan for using anti-submarine mines in an offensive defensive against submarines.
I. I submit herewith a plan to materially reduce the loss of merchant ships from submarine attack by causing the destruction of enemy submarines when they attempt to operate against merchant ships in waters where the plan is employed.
2. In brief the plan is as follows:-
In areas where shipping is most congested, require all ships to move along fixed lanes of travel about eight miles wide and mine these lanes with anti-submarine mines placed at depths fifty to seventy-five feet below the surface. The lanes so mined will be perfectly safe for surface craft, but will cause the destruction of any submarine attempting to operate in them submerged. This will result in immunity from submarine attack for all vessels in the lane.
3. Ocean traffic is most congested in the waters adjacent to France and England, and it is in these waters that the vast majority of submarine attacks occur. Naturally submarines operate where they can exact the greatest toll, but the waters near France and England especially suit them to operate in since those waters are to some extent protected and are shoal enough to permit the submarine to rest on the bottom when advisable. If we can prevent attacks on shipping in these waters we will greatly increase the submarines operating difficulties, will increase enormously the area they must cover, and, in the same proportion, will reduce their effectiveness against our shipping. The fact that the waters are shoal makes it possible to carry out this mining plan effectively and if we do mine the lanes as I suggest, the submarines must cease to operate against ships in the lanes or else sooner or later suffer destruction.
4. While I do not wish to belittle the value of mine barrages in preventing the submarine from getting to sea, such barrages present many difficulties for us. Among other drawbacks are the following very serious ones:-
(I) The mine barrage must be laid in the enemy’s sphere of action, which calls for a heavy protecting force while laying it and makes the laying most difficult.
(2) It requires a heavy and constant patrol to prevent the enemy clearing passages through it.
(3) It requires a large and constant patrol of anti-submarine craft to force the submarines to submerge on crossing the barrage.
5. The plan I suggest has none of the above disadvantages, since -
(I) The mines are laid in waters denied to all enemy surface craft, with the result that they can be laid carefully and accurately, and without great danger, or the use of many covering vessels.
(2) Enemy sweeping operations against the field can be carried out only under cover of a heavy protecting force operating in waters dominated by our forces.
(3) The field will be effective against submarines without employment of a patrol force to drive them down on the mines as the submarine must submerge on the mines if they attack ships in the mined lane.
On the other hand the plan has one great advantage in that it forces submarines to come into the mined area if they wish to attack shipping where it is most congested.
6. Apparently the only measure the enemy can hope to take against this plan (short of abandoning that field of operation)) is to himself mine the lane with anti-surface craft mines. He could do that only with difficulty and certainly not effectively. All such efforts would be nullified by the use of paravanes or by sweeping operations that keep the lane cleared to a depth of seven fathoms, which operations are entirely feasible.
7. I am submitting herewith a chart showing roughly my general idea of how the lanes should be laid. At the sea end of a channel lane is found another lane approximately normal to the channel lane, which I will call the “sea lane”. The purpose of the sea lane is to afford a wide front on which ships can enter or leave the protected waters. Ships going out follow the channel lane to the sea lane and then the sea lane until they reach points widely dispersed. Ships coming in remain dispersed until in the sea lane, after which they merely go in along the lanes in safety. A study of the best way to utilize the lanes during daylight and to avoid them during darkness should add materially to their effectiveness. A use of patrol boats beyond the sea lane front would permit still wider dispersion before entering or after leaving.
8. I believe lanes eight miles wide would furnish ample protection to all ships within two miles of the center line, which center line might be marked by heavy buoys and all ships required to keep on the right hand side of the center to prevent collisions. A lane eight miles wide would require about 200 miles [i.e. mines] per running mile to make it effective. This calls for a very large number of mines but probably not a greater number than would be required to maintain a proper barrage in the North Sea. The proximity of good mining bases would permit the field to be laid quickly and the whole operation would be infinitely easier to carry out than one in the North Sea. I am convinced that this plan will result in a greater destruction of submarines for the effort involved than the barrage plan will, since the destruction should be in exact proportion to the number of submarines that attempt to operate in the area, while in the barrahe [i.e. barrage] plan the destruction will be only in proportion to the success with which the barrage can be laid and maintained, combined with the success our patrol obtain in forcing the submarines down on the barrage. Even if the plan does not accomplish the destruction of a great many submarines it will, at least, force them to operate outside the congested zone, where the difficulties are enormously increased and our losses more than proportionately decreased. This alone would insure the failure of the enemy’s submarine campaign.
9. I suggest that this plan be compared most carefully with the barrage plan and that if it be not substituted for it, that it at least be used as an addition to it. Even though the broad plan be not carried out in detail it can be carried out easily in the Irish sea and approaches, and in other places where shipping is most heavily congested.
/s/ Harris Laning.