4. A mounted sentry stationed in advance of a picket line.
A cavalry vidette. Taking it easy [Edwin Forbes, artist]. Library of Congress Prints and Photographs Division, reproduction number LC-DIG-ppmsca-20611. (Cropped for presentation.)
According to Army Regulations:
- The sentinels and vedettes are placed on points from which they can see farthest, taking care not to break their connection with each other or with their posts. They are concealed from the enemy as much as possible by walls, or trees, or elevated ground. It is generally even of more advantage not to be seen than to see far. They should not be placed near covers, where the enemy may capture them.
- The sentinel should always be ready to fire; vedettes carry their pistols or carbines in their hands. A sentinel must be sure of the presence of an enemy before he fires; once satisfied of that, he must fire, though all defense on his part be useless, as the safety of the post may depend on it. Sentinels fire on all persons deserting to the enemy.
War Department, Revised United States Army Regulations of 1861. With an Appendix Containing the Changes and Laws Affecting Army Regulations and Articles of War to June 25, 1863 (Washington: Government Printing Office, 1863), 90, https://archive.org/details/101556516.nlm.nih.gov/mode/2up.]