The most important English ports, which handle 95 percent of foreign trade and which could not be adequately replaced by other harbours, are:
London } for the import of foodstuffs and
Liverpool } timber, the import and refining
Manchester } of oil.
These three ports, accounting as they do in peacetime for 58 percent of total imports, are of decisive importance.
Cardiff } for the export of coal.
Alternative ports, of limited capacity, and for certain types of cargo only, are:
It will be necessary to keep constant watch for any possible shift in the use of these ports. We must also seek constantly to compress and shift English foreign trade into channels which are open to effective attack by our own Navy and Air Force.
French ports need only be attacked in so far as they are involved, geographically or economically, in the siege of England, or are used as harbours for troopships.
6. In ports where effective minefields cannot be laid, shipping will be crippled by blocking the approaches to the ports with sunken ships and by destroying vital harbour installations. In this connection it is particularly important, in the harbours of
Manchester (Ship Canal)
to destroy the large sealocks upon which, particularly on the west coast, the regulation of the water level, and thus the effectiveness of the ports, depends.
7. In preparing these operations it will be necessary:
(a) To constantly check and bring up to date all facts known to us about English ports, their equipment and capacity, and about the English war industry and supply depots.
(b) To develop with high priority an effective means of employing aircraft as minelayers for anchored as well as floating mines.
(c) To provide a supply of mines sufficient to satisfy the very heavy demands and equal to the capacities of the Navy and Air Force.
(d) To ensure that the conduct of operations be the joint responsibility of Navy and Air Force, coordinated as to time and place by both services.
Preparations to this end will be undertaken as quickly as possible. I request Commanders In Chief Navy and Air Force to keep me constantly informed of their intentions.
I reserve to myself the right to decide the moment at which the restrictions imposed by my previous Directives for Naval and Air Warfare shall be lifted.
This will probably coincide with the opening of the great offensive.