Rear Admiral Sir William Reginald Hall, Director of Naval Intelligence, to Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters
There is reason to believe that the Mediterranean submarines will all return to Germany as soon as possible. The number will be about 30 and it is estimated that the bulk of them may begin to cross 52 degrees North to the Westward of Ireland about 11th November. Odd boats may be earlier. Their average spped will probably be about 10 knots. Intelligence of their movements may be difficult to xxxxxx obtain unless they are sighted by our forces enroute.
Source Note: Cy, DNA, RG 45, Entry 517B.