Chapter VI
The Sea Approaches and Coastal Waters
3rd September-31st December, 1939
Footnotes
3. See Map 9. Each convoy route was allocated a pair of code letters generally, but not always, having a 'self-evident' signification. Thus F.N. 6 would be the sixth northward-bound east coast convoy. H.N. stood for 'Homeward Norwegian', O.G. for 'Outward Gibraltar', etc. The addition of a third letter F or S signified Fast and Slow sections of the same convoy. For simplicity convoy numbers were not generally continued above 99 but were then restarted at 1. Thus it is possible to find two convoys with the same numbers whose sailings were separated by many months. The code letters of the principal convoy routes are given in Appendix J.
4. Appendix R gives monthly losses suffered by Allied merchant shipping and their causes.
6. See Maps 3 and 10 (facing pp. 63 and 97).
9. W. S. Churchill: The Second World War (Cassell & Co.), Vol. I, 2nd edition (1948), p. 453.
11. In later mines the polarity was sometimes reversed. These would not only be actuated by a ship built in the southern hemisphere but also by ships built north of the equator whose magnetism had been reversed by excessive 'de-gaussing'. Moreover the inclusion in a minefield of a proportion of mines of both polarities would double the work of sweeping since it would have to be swept for 'South Pole down' as well as for 'North Pole down' mines.
12. Unless specifically stated otherwise, the figures for merchant ship losses quoted throughout these volumes include Allied ships and neutral ships under British control as well as ships of British registry. They thus represent the best available estimate of the total damage done by the enemy's various weapons to the Allied cause.
15. See Map 10 (facing p. 97).
16. Details of U-boats sunk are given in Appendix K.