What is the key characteristic of a 'Breach' in military tactics?

The key characteristic of a 'Breach' in military tactics is breaking through enemy obstacles. A breach typically refers to a military operation that involves penetrating an enemy's defensive lines or fortifications to create a passage for forces to advance. This action is crucial as it allows friendly forces to exploit vulnerabilities in the enemy's defensive setup and proceed into deeper enemy territory.

In the context of military strategy, this characteristic emphasizes the offense, aiming to disrupt the enemy's ability to hold ground and to seize key positions or resources. Successfully executing a breach can determine the momentum of an operation, allowing forces to capitalize on surprise and achieve tactical advantages.

The other options, while relevant to military tactics, do not specifically define the concept of a breach. Maintaining contact with the enemy suggests a focus on engagement and intelligence rather than penetrating defenses. Defending a position is about holding ground rather than breaking through. Sneaking around the enemy's flank involves maneuvering but does not encapsulate the act of overcoming obstacles that defines a breach.