The element of surprise is essential to military effectiveness in both tactical and strategic operations, and requires the continuous concealment of capabilities and intentions.
OPSEC is the principal means of achieving that concealment. Military operations information is defined for the purpose of this Handbook as information pertaining to a strategic or tactical military action, including training, movement of troops and equipment, supplies, and other information vital to the success of any battle or campaign.
A classification guide should clearly identify the elements of information pertaining to the operational plan for which classification guidance is required.
Classification shall continue only so long as unauthorized disclosure would result in damage to the national security, which may be an indefinite period of time in the case of unexecuted long range plans.
Subject to change--since the secret consists of an arbitrary decision, it can be changed up to the time it is put into operation.
Perishable--once an attack has begun, the enemy knows the information.
What must be protected are operational concepts and their applications, and the capabilities, vulnerabilities, and weaknesses of the plan. The number, type, location, and strengths of opposing units. The capabilities and vulnerabilities of weapons in enemy hands, and how he normally applies the weapon. The morale and physical condition of the enemy force. In considering classification guidance for operations, there may be good reason to classify more information about the operation in the beginning than will be necessary later. Explanations of those terms are as follows: Compactness--a few words can reveal a major secret (e.g., the place and time of the World War II invasion of Normandy on June 6, 1944), which makes the secret easy to steal. Understandable--no special training or ability to understand is required in order to understand, evaluate, and transmit the secret. It needs to be stolen to be obtained (e.g., the time and place of the Normandy invasion).