The Supreme Commander Of The Armed Forces.
The Leader's Headquarters. 25th September, 1939. 7 copies
Directive No. 4 For The Conduct Of The War
1. The final form of Government of the former Polish territory in the area between the demarcation line and the German frontier has not yet been decided.
After the conclusion of hostilities around Warsaw and Modlin the demarcation line is to be adequately secured by formations of lower fighting power.
The forces of the Army and Air Force which are required for the quick destruction of the continuing Polish resistance behind the demarcation line (area San-Vistula-Narew-Pisia) will be retained in the east. I request a report on the strength of the forces which it is proposed to employ for both these purposes.
2. I shall myself decide whether Modlin and the part of Warsaw west of the Vistula are to be reduced by a general attack before 3rd October. This will depend upon the success of local attacks and the process of wearing down the enemy. Preparations will, however, be made for such an attack.
3. The flow of refugees westwards across the demarcation line will be halted at once, with the exception of refugees of German racial origin, and Ukrainian activists.
4. Decisions for the further strategy of the war will be made in the immediate future.
In the meanwhile no measures shall be taken by the Armed Forces, either in the matter of organisation or of equipment, such as may limit freedom of decision. The possibility of going over to the offensive in the west at any moment must be kept open. Sufficient forces must be retained in East Prussia to occupy Lithuania with all speed, even if there should be armed resistance.
5. (a) On land the Directives given for the conduct of the war in the west remain in force for the present.
(b) At sea, trade war according to International Prize Law is to be waged against both France and England, free from previous restrictions.
In addition, the following are now permitted: Attacks on French naval and air forces, French merchantmen in convoy, and all troopships; mining operations off the north French coast (embarkation points).
War on merchant shipping according to Prize Law by naval aircraft.
Attacks on passenger steamers, or large vessels which obviously carry passengers in considerable numbers in addition to cargo, will still be forbidden.
(c) For air warfare in the west the existing limitations remain in force. Aircraft will cross the German frontier only for purposes of local reconnaissance or to attack hostile aircraft and observation balloons. The Air Force may also operate in the German Bight and in the western declared mined areas, and in direct support of naval operations against English and French ships.
A separate order will cover long range reconnaissance.
6. With reference to submarine warfare, from now on only the following terms will be used:
For submarine warfare in accordance with Prize Law: trade warfare .
For unrestricted submarine warfare: the sea siege of England .
7. English merchantmen which are definitely known to be armed may be attacked by submarines without previous warning.