Which type of defensive operation emphasizes terrain and is utilized when troops have less mobility than the enemy?

The type of defensive operation that emphasizes terrain and is designed for situations where friendly forces have less mobility than the enemy is the area defense. This approach focuses on holding specific terrain features and utilizing them to control the battlefield effectively. By concentrating resources in key locations, forces can leverage the terrain to maximize their defensive capabilities.

In an area defense, troops fortify their positions and prepare to engage the enemy from advantageous sites, making the most of natural obstacles and enhanced defensive structures. This type of defense is particularly useful when mobility is limited since it allows forces to aim for a static yet resilient defense against a potentially more agile foe. By denying the enemy access to critical areas and applying concentrated firepower, the defending forces can inflict significant damage and regain the initiative through controlled engagements.

In contrast, other defensive operations like the mobile defense prioritize maneuverability and counteroffensive actions, while a retreat defense typically implies a strategic withdrawal rather than holding ground. Contingency defense similarly deals with plans for unforeseen future operations that may not focus on terrain as a priority. Therefore, the emphasis on terrain in an area defense makes it the correct choice for the situation described in the question.