What is the recommended action for a Marine displaying slow performance?

Increasing training intensity and focusing on speed drills is the recommended action for a Marine displaying slow performance. This approach is effective because it directly targets the areas where improvement is needed. By emphasizing speed drills, the Marine can enhance their muscle responsiveness, improve cardiovascular capacity, and develop better overall athletic performance. This method also encourages adaptation to the demands of physical activity, which can lead to improved speed and efficiency in various combat scenarios.

In contrast, the other options do not address the issue of slow performance in a functional manner. For instance, increasing rest and recovery time could lead to a decrease in overall physical readiness and may not challenge the Marine to improve their speed. Focusing solely on strength training may neglect the necessary speed components and doesn't directly improve performance in activities requiring quick movements. Reducing the number of repetitions could also diminish the practice needed to enhance speed and proficiency, ultimately hindering the Marine's ability to improve their performance.