Which guideline helps in positioning vehicles in a tactical environment?

Utilizing the topography of hills and gullies is crucial in a tactical environment as it allows for better concealment and protection of vehicles against enemy observation and fire. By positioning vehicles in a way that takes advantage of natural landscape features, operators can enhance their cover, making it more difficult for the enemy to detect or target them. This tactic also enables better mobility and defensive strategies, as vehicles can maneuver more effectively when they are using the terrain to their advantage.

The other options, while they might contribute to overall vehicle positioning strategies, do not provide the same level of tactical advantage as using the topography. For instance, using the cover of darkness is important but is not always applicable in every situation, as daylight operations may render this strategy ineffective. Spacing vehicles evenly is a good practice to avoid concentrated hits from enemy fire, but it doesn't leverage the natural defenses that hills and gullies provide. Finally, positioning vehicles away from the target area might mitigate the risk of being targeted but could leave them vulnerable to attack when they need to engage or maneuver rapidly. Therefore, utilizing the topography is the most effective guideline for positioning vehicles in a tactical setting.