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Preliminary (or pre-D-Day) reconnaissance is the reconnaissance that is used prior to the principal events of any major theater of war or landing force projection. The term is not similar to the initial word -reconnaissance-, as "preliminary reconnaissance" only prescribes the reconnaissance that is being conducted beforehand, and not during, any deployments, military operations, or movement of troops.
This method of intelligence-gathering generally operates within the highest military intelligence tiers, or level of the intelligence general staff, for intelligence collection management—as it allows the combatant, landing force, and/or task force commanders—to better situate and prepare troops for the best feasible deployment, or landing, to achieve the utmost advantage. Aerial and ground reconnaissance elements are collateral to preliminary reconnaissance since it may require both assets to gain the appropriate preliminary intelligence.
Examples of preliminary reconnaissance is best displayed when the United States Marines of the VAC Amphib Recon Company, during World War II, would reconnoiter the beaches and inland for their landing (task) force commanders, a method consecutively known as amphibious reconnaissance. The vital intelligence would dictate the actions of the commander's tactical battle plan of landing the troops ashore.