Which operation is defined by the need to gain time and protect the main body's movements?

The operation characterized by the need to gain time and protect the main body's movements is a guard operation. This type of operation involves positioning forces to prevent the enemy from interfering with the main body’s activities while allowing it to move more freely. The primary objective of a guard operation is to create a buffer against potential enemy engagement, thereby safeguarding the main forces from disruption and giving them the necessary space and time to execute their plans.

In a guard operation, troops are typically positioned in a way that allows for both observation and engagement of any enemy forces that approach the main body. This approach not only helps in delaying enemy actions but also ensures that the main unit can maintain its operational tempo without risking an encounter with the enemy that could lead to significant hindrances.

The other operations mentioned, such as screen, cover, and area security operations, serve different tactical purposes. For instance, a screen operation offers early warning and intelligence concerning enemy movements, while a cover operation provides greater protection but might not focus directly on gaining time. An area security operation emphasizes securing a specific area but may not have the same immediate focus on time gain and protection as a guard operation does.