Which characteristic provides a significant tactical advantage when controlled?

The correct answer is key terrain, as it refers to specific geographical areas or features that provide a significant advantage to the force that controls them. When a force occupies key terrain, it can enhance its ability to observe, engage, or directly influence operational outcomes in the surrounding area. For example, controlling a mountain pass, river crossing, or urban center can impact mobility and supply lines, affect command and control, and provide advantageous positions for weapon systems.

In contrast, while high ground does provide an advantage in terms of visibility and defensive capabilities, its significance relies heavily on the overall context of the battlefield. Similarly, a strategic position might be valuable but does not necessarily guarantee control over key terrain, which has a direct effect on the tactical situation. Operational depth involves maintaining forces and resources at various distances from the frontline, which is critical for long-term success but is not as immediate or directly influential as having control over key terrain. Therefore, controlling key terrain is what ultimately provides a profound tactical advantage.