Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters to Rear Admiral Henry M. Wilson, Commander, United States Naval Forces in France
Chronological Copy. File No. <11-2-1>
Cablegram Sent 8 Sept. 1918 LDR
To Comfran Brest Serial No. 6020
Prep. by C-1 SX D.R. D
6020. Concentration of submarines in Bay of Biscay undoubtedly has primary object of interrupting lines of communication between North American and French Atlantic ports and secondary purpose of covering approaches to English Channel, Bristol Channel and Irish Sea to and from westward and southward. Concentration since August 15 appears to be between Longitude 9 degrees and Longitude 14 degrees with maximum intensity at Longitude 10-30 and between Latitudes 46 and 48-30 with maximum intensity at Latitude 47-15. The lower limit of position seems to be about Latitude 46 degrees <N>. It is evident that the position chosen by the enemy is a strategical one, but that it cannot be greatly varied without sacrificing combined purposes mentioned. If concentration is moved in any direction from present position it is certain that one or other of objects will be defeated. Considered unlikely that main concentration will be moved appreciably to southward, as from southward present blockade is effective only against French Atlantic ports and amount of shipping in these ports will probably not justify concentration. Concentration can readily be moved to northward, however, where large volume of shipping is certain to be encountered. Main concentration is not likely to be moved unless results are unsuccessful.
Area covered by submarines is selected so that vessels normally making coast at daylight must pass through most of area during daylight. Submarines are deployed on different meridians, so that submarine sighting convoy can communicate with others farther along the course and enable them to take favorable positions for attack. Several instances have been noted where submarine sighting convoy communicate with others farther along the route. Routes with several marked changes during daylight greatly assist in defeating this plan. Considered important also that ships pass through the most dangerous submarine areas at night, except on moonlight nights. This in itself makes it difficult for any submarine to find a convoy and limits possibility of other submarines delivering attack farther along route. 115108 6020.
Source Note: Cy, DNA, RG45, Entry 517B. Date confirmed by time date stamp at the end of cable.