The commander may find in the expression of his task a statement, only, of the action required. For example, the order "Proceed toward the enemy battle line" involves movement, indicating merely a change in relative position. No provision appears as to a future condition or state of affairs. Again, the task may be expressed as an order to "Attack the enemy battle line." In this case, the enemy battle line is the physical objective, but no specific future condition to result from the attack is indicated. Here the action and the physical objective are given, but the objective is left to be inferred. If the commander can ascertain, from the directives he receives, his task expressed in terms of accomplishment, he may be able to visualize the action, the physical objective, and the condition to be created. The order "Destroy the enemy battleship" (indicating, as the objective, "the destruction of the enemy battleship"), results, when successfully completed, in a new condition which is the objective of the action against the physical objective. Accordingly, a task expressed in such terms of accomplishment conveys precise information as to the objective; yet such an expression of the task does not prevent freedom of action, with opportunity for exercise of initiative. The commander who is assigned such a task can clearly visualize the results demanded of him, and may feel at liberty to employ any one or all of the methods at his disposal. However, it is not always possible or even desirable to express tasks in terms of accomplishment. For example, where the future situation cannot be adequately visualized, either because of the doubtful values of certain factors or because of possible changes in circumstances, it may be impracticable to assign a definite task in terms of accomplishment. Under such conditions, and sometimes for other proper reasons, it may be desirable to afford a trusted and competent subordinate a corresponding measure of freedom of action. In such a case, the indication of the commander's general objective for his entire force, together with a directive for action along a certain general line, without prescription of a definite objective, may be especially appropriate to the situation. Such is the frequent usage in the issue, for example, of directives of the type known as letters of instruction (Chapter VIII). Again, where immediate response is desired, and where the objective may be understood by implication, the task may be better expressed in terms of action, rather than of accomplishment. This is frequently the case where the task is assigned by word of mouth, by memorandum, or by signal. In the last-named instance, the signal, when it constitutes a command fully understood by previous usage or experience, may convey a practically instantaneous comprehension of the objective. In many such instances, however, an inferred objective will require more analysis.