Naval History and Heritage Command

Memorandum from Commander Edward McCauley, Jr., Acting Director, Office of Naval Intelligence

OFFICE OF NAVAL INTELLIGENCE

Subject

or        Anti-Submarine Warfare-Statistical report, with conclusions.

Title.

Source

and       X-452, July 25, 1917.

Date.

V E R Y C O N F I D E N T I A L

SUBJECT   Statistical report on Anti-Submarine warfare, from beginning of the war and until March 31st, 1917; with conclusions thereon.

From X    No. 425(D.F.B.).    Date July 25th, 1917.

Replying to O.N.I. No.        Date

     1.   Admiralty returns of March 31st, 1917, give the number of German submarines built and building (including losses) as follows:-

     Ocean-going and instructional      130

     Coastal                                       65

     Minelaying                                  99

          Total                                   294

     2.   The known German losses up to and including March 31st, 1917, have been as follows:-

     Ocean-going                       29

     Coastal                              11

     Minelaying                         13

          Total                            53

     3.   Therefore, during April 1917 – the month during which the Allies suffered the heaviest shipping losses from German submarine – there were probably in commission some 101 ocean-going and instructional, 54 coastal, and 86 minelaying German submarines.

     4.   The rate of increase of German submarines is generally accepted as three per week.

     5.   It appears from the returns that the rate of destruction since the beginning of the war is as follows:-

     Known cases – One every two months

     Known and probable cases – Three per month

     Known, probable and possible cases – Five per month.

     6.   It therefore seems that the rate of increase in numbers of German submarines is practically double the rate of known, probable and possible losses, and some 25 times greater than the known losses.

     7.   The following table gives in brief the results of various methods of anti-submarine warfare during the war and until March 31, 1917:-

     8.   A summary of known submarine losses – results given in percentages for the various methods employed in anti-submarine warfare – here follows:-

1.   By accidents, such as explosion of their own mines, striking German mines, stranding, etc. – 32%

2.   By destroyers (gunfire, ramming, depth charges, paravanes, etc.-                                  17%

3.   By decoy ships              17%

4.   By submarines               15%

5.   By nets, smacks, etc. -     8%

6.   By mines                        6%

7.   By men-of-war of types other than those mentioned above                                  6%

8.   By merchantmen             0

     9.   With an idea of later drawing some conclusion relative to the most successful method of anti-submarine warfare, the following table is here included – this table refers to losses in home waters:-

     10.  It is evident that conclusions drawn from such small losses by so many various methods of destruction are not convincing. The only positive conclusions are (1) the large German losses from their own accidents – 17 total, four of which occurred during the first quarter of 1917 – and (2) the total failure of merchantmen to inflict destruction upon German submarines. However, it is interesting to note that destroyers, decoy ships, and submarines are undoubtedly responsible for whatever success has attended the anti-submarine campaign: and taking into account the mission of German submarines, i.e., to devote exclusive attention to destruction of merchant shipping, the following conclusions, based partly upon experience in the past and partly upon speculation as to the immediate future, seem to be logical:-

I.   The Germans can inflict considerable losses on Allied destroyers whenever the latter seriously interfere with the German submarine mission, unless the destroyers travel together in such numbers as to insure counter-attack.

II.  Merchant ships have inflicted no losses on German submarines; and it does not appear that they can do so.

III. From the above, and aside from other obvious reasons, it appears that the convoy system will not only reduce the loss to merchant shipping, but will allow the concentration of destroyers necessary for inflicting losses on German submarines.

IV.  The Germans can, if they will, nullify the decoy ship successes, by remaining submerged until the decoy ship sinks, or by sending out the large type of submarine – the rumoured type – that can inflict severe gun fire injury and insure the destruction of vessels of this type.

V.   There remains, therefore, the Allies’ own submarine to meet the German submarine on an equal footing; and whatever may be the development of the German submarine as to size, etc., to ensure successes against destroyers and decoy ships, the Allies’ submarine remains on an equal fighting foot with the German. And accepting the opinion that the German torpedo is now defective – due to lack of material, hasty assembly, lack of proper standardization of speed, etc., - it would appear that the advantages to the Allies’ submarine should increase in future rather than decrease.

VI.  The above opinions bear upon immediate military operations only. Should satisfactory detectors be developed, no conclusions drawn from the past or present experiences would supply, and then suppression of the German submarine campaign would not present any particular difficulty.

VII. Until such detectors are in general and efficient use, it would appear reasonable to expect the best returns from the Allies’ submarines.

E McCauley

acting