Final answer:
Objective locations, rally points, phase lines, checkpoints, and axis of advance require a 6-digit grid and terrain features.
Step-by-step explanation:
To answer this question, we need to understand what a 6-digit grid and terrain features are. A 6-digit grid is a method of identifying a specific location on a map using a grid system. Terrain features refer to physical characteristics of the land, such as hills, rivers, and forests. Now, let's look at each option and determine which ones require a 6-digit grid and terrain features:
Option A: Objective locations and rally points are specific locations on a map that require precise identification, which can be done using a 6-digit grid. Phase lines, checkpoints, and axis of advance also require accurate positioning, which can be determined by considering the terrain features.
Option B: Commander's intent, concept of operation, main effort, supporting effort, and reserve do not necessarily require a 6-digit grid or terrain features.
Option C: Reconnaissance, security, main body, support, and attack by fire are more related to operational concepts rather than specific locations on a map.
Option D: Fire support plan, logistics plan, medical plan, and communications plan are operational plans that do not depend on a 6-digit grid or terrain features.
Based on the above analysis, the correct answer would be Option A) Objective locations, rally points, phase lines, checkpoints, and axis of advance.