An example might occur in a situation where the commander has received an order to "Protect the base at A". It is then supposed that, after estimating the situation, he has reached the Decision "to deny the enemy the use of base sites within effective bombing range of A", the purpose of the Decision being, of course, "in order to protect the base at A". The action required might then be undertaken in two stages. The first stage might be confined to the area ABCD. If, then, all available base sites in this area, except Y island, were already securely in friendly hands, the commander would find it necessary to make provision for an operation to deny the use of this island to the enemy. If this operation is of such a nature that the commander desires to execute it under his own direct control, instead of assigning it to a subordinate, it presents a subsidiary problem which the commander, himself, has to solve.
The commander has now determined the necessity of solving a subsidiary problem relating to the accomplishment of a designated part of his general plan. He has also determined the necessity of solving another subsidiary problem presented by an operation pertaining to the first stage of the accomplishment of his general plan.
Each subsidiary problem requires an estimate of the situation although "the brevity of the mental process tends to obscure this fact" ([page 172]).
In making his basic estimate, the commander may have discovered the need for these subsidiary estimates. In this case, he may have included them in his estimate, as "estimates within the estimate" ([page 83]), in his analysis of the operations involved in the various courses of action which he considered. For instance, his basic Decision may have included the capture of Y island, and he may have covered this feature by a corollary to that Decision, as follows:
Corollary: As a first stage, to deny the enemy the use of available base sites in the area ABCD, by capturing Y island.
However, the commander may not discover the desirability or need of solving these subsidiary problems until the second step, when resolving the basic Decision into the detailed operations required. In this case, he might make due provision at that time for the operations involved in the subsidiary problems. The mental procedure would be the same in either event.
The commander may find, however, that he prefers to make a separate, subsidiary estimate with respect to the determination of the stages of his operation, including the details as to the performance of the first stage. In this case he finds a proper mission for his subsidiary estimate in the basic Decision, linked to its purpose. This mission would be as follows:—
(Task) To deny the enemy the use of base sites within effective bombing range of A,
(Purpose) in order to protect the base at A.
During the subsidiary estimate the commander may discover, in his study of the area ABCD, the necessity for an operation to deny Y island to the enemy, and may even go so far, in this study, as to decide on the capture of this island. The decision, settling on this area as the scene of the first stage of his effort, may then include provision for the capture of the island, as follows: