Army of observation

An army of observation is a military body whose purpose is to monitor a given area<ref name="A Military Dictionary: Or, Explaination of the Several Systems of Discipline of Different Kinds of Troops, Infantry, Artillery, and Cavalry; the Principles of Fortification, and All the Modern Improvements in the Science of Tactics: Comprising the Pocket Gunner, Or Little Bombardier; the Military Regulations of the United States; the Weights, Measures, and Monies of All Nations; the Technical Terms and Phrases of the Art of War in the French Language. Particularly Adapted to the Use of the Military Institutions of the United States"> or enemy body in preparation for possible hostilities.

Some of the more notable armies of observation include:
 * Third Reserve Army of Observation, a Russian army tasked to monitor the Austrian border in 1811 prior to the French invasion of Russia
 * The army of observation at Fort Jesup, Louisiana, United States, which monitored Texas' transition from Spanish to Mexican control, and eventual independence
 * The Hanoverian Army of Observation which monitored the border prior to the 1757 Invasion of Hanover