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: Decision: To deny the enemy the use of base sites in the area ABCD as a first stage toward denying him the use of all base sites within effective bombing range of the base at A. Corollary: To capture Y island. However, the commander may not take up the matter of denying Y island, specifically, to enemy use until he studies the detailed operations required for the accomplishment of the action involved in his first stage. In such event, he may make provision for the capture of the island in his subsidiary plan for the execution of the first stage. He may find, on the other hand, that he prefers to make a separate, subsidiary estimate as to this feature. If so, the mission for this subsidiary estimate would be identical with the decision (less the corollary, but plus the purpose of the estimate), i.e.,-- (Task) To deny the enemy the use of base sites within effective bombing range of the area ABCD as a first stage (Purpose) toward denying him the use of all base sites within effective bombing range of the base at A.