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.
During this estimate the commander considers the various courses of action whereby he can deny to the enemy all bases in the area of the first stage. Concluding that Y island is the only base site not securely in friendly hands, and that the best method of denying it to the enemy is to capture it himself, he reaches a decision as follows:
Decision: To capture Y island, in order to deny to the enemy the use of the only available base site in the area ABCD.
In each of the foregoing cases, the commander is said to have "deduced" the mission for his subsidiary problem. As has been demonstrated, the process of deduction is merely the application of the natural mental processes through the use of the estimate of the situation. Whether the estimate is formal or informal, detailed or brief, written or mental, is immaterial; in any case, the estimate results in a decision which provides, with its purpose, a proper mission for the succeeding problem which has been presented by solution of its predecessors.
In logical sequence, from problem to problem, the procedure outlined in the preceding discussion enables the commander to derive a correct mission for the problem involving the capture of Y Island. Clear visualization of such a subsidiary mission is frequently of great importance, and may be difficult unless the procedure has been carefully traced from each problem to the next. In this particular example, if the commander finds that the capture of Y Island is of such a specialized and localized nature ([page 170]) as to call for a formal estimate (as may frequently be the case in capturing a well-defended island base), he will be especially desirious of deriving a correct (subsidiary) mission as a basis for this estimate. In this instance a correct mission would be:—
(Task) To capture Y Island,