is begun, considers the changing situation as a variable in the
problem presented for his solution by the original (basic) situation.
With the march of events, he is, therefore, constantly critical to
detect whether variations from the original situation are in
accordance with his design or whether these variations have introduced
new incentives which demand modification or alteration of his plan, or
its complete abandonment.

The fourth step is discussed and developed in Chapter IX.

Sequence of Events in the Four Steps

When all of the elements of the entire procedure of the four steps are
present, they take, from the viewpoint of the same commander
throughout, the following form:

(1) First step: The commander, confronted with a strategical situation
(page 83), makes a strategical estimate and comes to a strategical
Decision. The problem, the estimate, and the Decision are basic.

(2) Second step: The commander now is confronted with a particular
problem, one proceeding from his basic problem and involving the
details of a plan of execution to carry out the Decision reached in
the first step; this problem consists, itself, of numerous other
problems of detail, which require solution by the commander himself.
The basic Decision has embodied an outlined plan, strategical in
nature, for an operation to accomplish the motivating task of the
first step. This plan requires resolution into the detailed operations
necessary for its full accomplishment.

Each such detailed operation, as part of the outlined plan embodied in
the strategical Decision, calls for a proper estimate. Though usually
not formal in nature, more especially if the necessary data can be
found in the basic estimate, such estimates are fundamentally the same
as for the basic problem. The assembly of such detailed operations
results in the formulation of a basic plan.

At this point, additional problems may present themselves, these being
frequently tactical in nature. Such, for example, may be sortie plans,
approach plans, and Battle Plans. Other specialized plans (training,
intelligence, logistics, etc.) may be needed. The data essential for
the solution of such problems are more detailed than for the usual
strategical basic problem. In some instances, such subsidiary plans
may be developed directly from the basic Decision by procedures
distinctive of the second step. In other instances, solution may
require an additional subsidiary estimate,