The Government War Book was assembled in three parts reflecting pre-Precautionary Stage matters, the Precautionary Stage, and War. The War Book specifies the actions to be taken by ministers and officials in each of these periods. These might be: immediate and vital security measures which require decision at the earliest possible moment when there is a threat of war; institution of the Precautionary Stage and the principal measures which would automatically be brought into operation during the course of that Stage; measures which require separate Cabinet decisions during the Precautionary Stage; and measures required with the onset of war.
It had been laid down by the Cabinet Defence (Transition) Committee that in addition to the Government War Book each Department of State should maintain a departmental war book.
The series includes some records of Exercise Felstead: a simulation by officials of the Cabinet and the Defence (Transition) Committee discussions during a crisis. The official group was designated GEN 772, and additional records are at CAB 134/187.
A key planning assumption around which the War Book was prepared was that at the outset of a fresh war emergency a new Emergency Powers (Defence) Bill would be presented to Parliament. The bill would provide for the introduction of sets of defence regulations within each of the principal departments' areas of competence.
The war books have been subject to a virtually continuous process of revision and amendment.