ADP 3-90, page 82

Chapter 5 5-2 ADP 3-90 31 July 2019 and significant changes in terrain trafficability. Although all units conduct reconnaissance, ground cavalry, aviation attack reconnaissance units, scouts, and special forces are specifically trained to conduct reconnaissance operations. Some branches, such as the Corps of Engineers and Chemical Corps, conduct specific reconnaissance operations that complement the force’s overall reconnaissance effort. However, BCT, division, and corps commanders primarily use their organic or attached reconnaissance—ground or air—and intelligence elements to accomplish reconnaissance. 5-5. The five types of reconnaissance operations are—  Area reconnaissance is a type of reconnaissance operation that focuses on obtaining detailed information about the terrain or enemy activity within a prescribed area. Commanders assign an area reconnaissance when information on the enemy situation is limited or when focused reconnaissance will yield specific information on the area in question. An area reconnaissance differs from a zone reconnaissance in that the unit conducting an area reconnaissance starts from an LD.  A reconnaissance in force is a type of reconnaissance operation designed to discover or test the enemy’s strength, dispositions, and reactions or to obtain other information. A commander assigns a reconnaissance in force when an enemy force is operating within an area and the commander cannot obtain adequate intelligence by other means. The unit commander plans for both the retrograde or reinforcement of the friendly force (in case it encounters superior enemy forces) and for the exploitation of its success.  Route reconnaissance is a type of reconnaissance operation to obtain detailed information of a specified route and all terrain from which the enemy could influence movement along that route. Route reconnaissance provides new or updated information on route conditions, such as obstacles and bridge classifications, and enemy, adversary, and civilian activity along the route.  Special reconnaissance is reconnaissance and surveillance actions conducted as a special operation in hostile, denied, or diplomatically and/or politically sensitive environments to collect or verify information of strategic or operational significance, employing military capabilities not normally found in conventional forces (JP 3-05). Special reconnaissance provides an additional capability for commanders and supplements other conventional reconnaissance and surveillance actions.  Zone reconnaissance is a type of reconnaissance operation that involves a directed effort to obtain detailed information on all routes, obstacles, terrain, and enemy forces within a zone defined by boundaries. Obstacles include existing, reinforcing, and areas with CBRN contamination. Commanders assign a zone reconnaissance mission when they need additional information on a zone before committing other forces. Zone reconnaissance is the most time- and resource-intensive form of reconnaissance. SECURITY OPERATIONS 5-6. The main difference between conducting security operations and reconnaissance is that security operations orient on the force or facility being protected while reconnaissance orients on the enemy and terrain. Security operations aim to protect a force from surprise and reduce the unknowns in any situation. Commanders conduct security operations to the front, flanks, or rear of a friendly force. Security operations are shaping operations. As a shaping operation, economy of force is often a consideration when planning. 5-7. The four types of security operations are—  Area security is a type of security operation conducted to protect friendly forces, lines of communications, and activities within a specific area. The security force may be protecting the civilian population, civil institutions, and civilian infrastructure with the unit’s AO.  Cover is a type of security operation done independent of the main body to protect them by fighting to gain time while preventing enemy ground observation of and direct fire against the main body. Commanders use the cover task offensively and defensively. (Cover as a doctrinal term also has other definitions.)