The overall objective of the research is to summarize tactical considerations, resulting from terrain and weather analysis, to support the preparation, planning and execution of subterranean operations. The study used the Grounded Theory for collection, analysis, and systematic treatment of data. The main data sources for the study consisted of purposive sampling from operations in subterranean systems and lessons learned from them. Two new sub-variables are now proposed to be included in terrain and weather variable from mission analysis model for subterranean operations: Subterranean system’s location and accesses and subterranean system features. The key to finding subterranean systems is through terrain analysis, physical ground search, operational indicators, and intelligence products. The analysis of the features of the subterranean system and its mapping is critical for developing courses of action. Forces must be trained and equipped to manoeuvre and combat at short distances and poor visibility conditions. Surface access points and command and control bunkers usually are assessed as key terrain. Obstacles placed at intersections are excellent ambush sites. Accessing sophisticated structures requires specific techniques and equipment. Inside the subterranean systems, existing angles, barriers, walls, cavities, stairwells and other objects provide cover and concealment. Water can make it impossible to build subterranean systems, place obstacles, or even use them; droughts can “create” new avenues of approach. Clouds and fog difficult the detection of subterranean systems. The terrain and weather analysis model, the characteristics, and the tactical considerations presented, all combined, support the preparation, planning, and execution of operations in subterranean systems.