Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters, to Secretary of the Navy Josephus Daniels
[Letter No. 17]
Office Vice Admiral Commanding
United States Destroyer Forces, European Waters,
London, July 6, 1917.
From: Vice Admiral William S. Sims.
To: Secretary of the Navy (Operations).
Subject: Procedure concerning protection of Army convoys in trans-Atlantic passage.
1. As it is apparent that the responsibility for the safe passage of troop convoys through the submarine area should be placed upon the commander of the escorting forces in that area, who has latest information as to enemy movements, I herewith submit my recommendations as to the procedure which I consider necessary for safety of future troop convoys.
2. These recommendations are based upon actual experience with the four convoy groups which have already made passage and after a thorough consideration of all British Admiralty war experience in connection with such convoys.
3. The greatest danger in connection with troop convoys lies in the possibility of interception by enemy of cable and wireless communications in connection therewith.
The below recommended procedure is therefore based on this consideration-that is insurance against any information reaching the enemy as to routes followed and prospective movements of convoys in time to be of any use to him.
I can not too strongly urge against all wireless communication between ships of convoy or between convoy and the shore except in cases of extreme necessity.
I must also lay great stress on the necessity of my having definite information as to the time when escorting forces will be necessary.
The destroyers available for escort duty, as has been reported to the department, are also absolutely essential to the safety of vital merchant convoys. And in addition they must be prepared at all times to take advantage of any opportunity for effective offensive operations against the enemy.
It is therefore absolutely necessary that I be enabled to plan in advance and to coordinate all work of the destroyers in the submarine zone.
4. The following specific procedure, stated in the order of its occurrence, is therefore recommended:
First. Notify me in British Admiralty codes as far in advance as possible of (a) probable date of sailing of convoy group, (b) the number of ships, and (c) anticipated average sea speed.
This communication should contain no information as to routes to be followed or rendezvous to be made.
Second. Issue sailing orders to the convoy group in the manner prescribed below, and concerning which the greatest possible secrecy should be maintained, not even the essential parts of the orders to be known generally to officers or clerical staff of the department, or, in fact, by the convoy group commander himself until after he has sailed.
Select a meridian which will be known hereafter as the standard meridian. I recommend the thirtieth, and will assume in the absence of contrary instructions that the department hereafter in referring to standard meridian will refer to the thirtieth.
Select in the Navy Department a latitude in which the convoy group in question should cross the standard meridian. In cabling this latitude add 3° to it for purposes of deception. In absence of contrary instructions, I will understand that a constant figure of 3° will always be added to the actual latitude in which the convoy will cross the standard meridian.
Also decide upon a definite time at which the convoy group in question should cross the standard meridian in the latitude selected.
In selecting this time due leeway should be allowed for heavy weather and other casualties which may reduce the convoy below its anticipated sea speed. For example, if the convoy should encounter good weather and find itself in advance of scheduled time, it should deliberately slow down sufficiently to insure its passage through the point selected at the time previously arranged. This affords us on this side definite information as to where the convoy will be at a certain specified time, and this without the necessity of any further communication with the force itself from either side. Such increase in the time required to make the passage as results from this procedure is of no consequence in comparison to insuring the safety of the convoy.
After the convoy is joined by the escorting destroyers it will, of course, proceed at maximum speed.
Third. On the days of departure of the convoy group cable me in British Admiralty code a message such as follows:
"Convoy group No. 1 latitude 49 N. 10 a. m., August 21."
I will understand this message to mean that convoy group No. 1 (as previously reported) sailed on the date of this dispatch, and that it will cross the standard meridian (the thirtieth) in latitude 46 (49 minus 3) at 10 a. m., July 21.
On this information I will be enabled to prepare in adequate time definite sailing orders for the escorting destroyers and issue the necessary instructions to insure their readiness for duty in question.
In the case here used for illustration I would understand that the convoy group passing through latitude 46 N., longitude 30 W., on August 21, would proceed on a course at its average sea speed direct for its destination.
The escorting destroyers will receive orders to intercept the convoy group on this line, and well to the westward of the dangerous submarine zone. And they will also have orders as to any necessary diversion from the direct route on the way to their destination. They will also be kept informed of the latest news at all times direct from Queenstown as to enemy movements.
Fourth. The destroyers, after joining with the convoy group will inform me in a special secret code of the approximate time and latitude in which they will cross a certain meridian-usually the tenth.
This information will reach me through Queenstown station, and will enable me to notify the French ministry of marine in order that any necessary mine sweeping may be done, and that French torpedo boats may be on hand off the port to give any necessary instructions as to the method of approaching the port.
5. To sum up, two dispatches only would be sent to me from the department. I would send nothing in return except acknowledgements.
The first of the two dispatches should be sent as far in advance of sailing as it is possible to anticipate approximately the time. This dispatch is particularly important, because if I should find that the prospective arrival in the submarine zone of troop convoy should coincide with the arrival of a merchant convoy it might be necessary to request a delay of one or the other.
The second dispatch, which states only latitude, date, and time of crossing the standard meridian, gives no information of essential value to the enemy, because the standard meridian is not mentioned in any dispatch.
6. I would strongly recommend that no other cable or wireless communications be sent except in case of extreme necessity; and further that the convoy itself be directed to carefully avoid wireless communication except such as may be necessary at very low power for communication with destroyers when they reach a relatively close position.
7. The convoy commander should be directed to accept the advice of the senior destroyer commander as to courses and speed and formation after escorting destroyers have joined. They will have the latest information as regards enemy movements, and it will also be possible, if necessity arises, to communicate with them from their headquarters at Queenstown, where the latest developments are always known.
8. I would strongly recommend that no communication be made with the French shore. It is very unwise, as long as sufficient escorting destroyers are sent from Queenstown, for French men-of-war to attempt to meet and escort our convoys in, except when they arrive near their destination, to give them information about channels, etc. Such a course necessitates radio communication in a code which is now well known to be compromised. There is also great danger of misunderstanding on account of difference of language.
I have thanked the French ministry of marine for the courtesy extended and protection afforded by the French vessels which were sent to meet our first four troop convoys. They were sent primarily as a courtesy in view of the historical significance of the occasion. I am in constant touch with the French ministry of marine and there will be no misunderstandings. I think it very undesirable to send communications concerning the movements of the convoys to the French ministry of marine as well as to me. I will keep them fully informed to such extent as may be necessary in arranging or arrival of the convoys.
9. One of the first essentials in the movements of shipping in the war zone is it should never stop or even slow down, but should proceed to destination at maximum speed, regardless of circumstances. If, for example, in heavy weather, the escorting destroyers should not be able to join, the convoy should disperse and proceed independently at maximum speed, and zigzagging. This is the practice of the British service. There is little danger of submarine attack in such heavy weather.
Likewise, in case of fog or other unusual conditions, if the convoy should become separated, it is much the wiser course for each ship to proceed independently rather than to attempt to reassemble by changing course, slowing down, and sending numerous wireless communications.
10. All interally codes and merchant codes are unreliable. There is good reason to believe that they are in the hands of the enemy. It is therefore entirely essential to safety that radio communications, when necessary, be confined to the latest United States or British naval codes with ciphers. Our destroyers are equipped at all times with such codes. Any necessary communications while en route which can not be foreseen should be made preferably by destroyers, which have the code, “Vice Admiral, Queenstown,” who will take the necessary steps and keep me fully informed in case of my absence from Queenstown.
11. Briefly stated, when the convoys have reached the submarine zone they should act under the guidance of the escorting destroyers, subject to orders of the commander in chief at Queenstown (the command under which they are operating at all times). I am kept fully informed at all times as to all duty being performed by our destroyers there, and accept full responsibility for all orders which emanate from Queenstown to or via our destroyers. They are thoroughly familiar with the policies and methods of communication in use in Queenstown area, and it is highly desirable that they should continue under the same policies and methods as those with which they are constantly working in the war zone.
12. I would cite an incident illustrating the great danger of attempting to communicate to more than one headquarters. Although every measure had been taken for the escorting and safe passage of convoy group No. 1 through the submarine zone, and all necessary orders had been issued with the full cognizance of French and British admiralties, a dispatch in the "French, Russian, English" code was intercepted between the Seattle and Brest.
Not only was this dispatch sent in a code which is considered very unreliable, but it was also either coded very poorly or garbled in transmission, and for this reasons, and also the nature of the dispatch itself, further radio communication was undoubtedly necessary. The dispatch asked where French men of war would join the first group. This was entirely unnecessary, as all arrangements that could be made concerning the question had been made in advance. Even in case the French torpedo boat failed to join before the group reached the coast, it was very inadvisable to attempt to communicate with the French Admiralty, particularly with an unsafe code. The convoy group was under escort of six destroyers, which is more than is usually assigned to troops convoys of such a size.
13. I trust that the Department will see fit to adopt the recommendations contained in this letter, which will involve placing full responsibility on me for handling the convoys while in dangerous waters. I am convinced that the principal danger to be considered is preventing the enemy from intercepting cable dispatches as to the movements of convoys on the high seas. Hence the necessity for a minimum amount of communication and the undesirability of selecting a series of rendezvous and having to constantly refer to them in dispatdhes between the department and myself and between me and France and between the various stations involved in England.
It will be observed that the method suggested is “iron clad” in this respect, namely that even if all the messages indicated were intercepted and translated by the enemy there is no information in them which would enable them to intercept a convoy on any parts of its route, since the standard meridian is not mentioned and three is added to the latitude.
It is true that the method involves the inconvenience of having the convoy reach the standard meridian at a prescribed time; but we can always be sure that it will not cross this line ahead of time, and if it is somewhat late this means only that the destroyers will have to wait for it. But even this inconvenience can be avoided, except in very exceptional circumstances, by allowing a sufficient margin between the maximum sea speed and that necessary to reach the standard meridian at the prescribed time.
As has previously been reported, a convoy of eight transports with an escort of eight destroyers is safer than two convoys of four transports, each escorted by four destroyers. See my letter of June 13, 1917.
Convoys should not follow each other at intervals of less than one week, because if a number arrive in quick succession they will require the absence of a great many destroyers from their patrol area at the same time.
As the escorting cruiser affords no protection again[s]t the attack of submarines, she should return to the United States as soon as the destroyers join the convoy, provided she has radius enough to do so. In the case of British convoys, the cruiser leaves the convoy as soon as the destroyers join it, and- proceeds to port (for coal, etc.) at full speed.
The British consider it essential that the convoy commander should always be on one of the escorted vessels (transport or merchant vessel). This because both the cruiser and the convoy should be free at all times to maneuver separately, the former to maneuver for attack and chase of a raider and the latter to maneuver to avoid the enemy.