I have no idea how often it was employed during the Civil War, but camouflet was a tactic
used by sappers, specialists in tunnelling under enemy defence walls. A tunnel would be
dug to intercept an enemy tunnel. Then an explosive charge would be placed where
enemy sappers extending their tunnel would be killed by it.

"Usually associated with defensive mines a camouflet was a small
explosive charge packed into a hole drilled from a mine defensive gallery
toward a hostile mine gallery. It was designed to fill the hostile mine
gallery with deadly fumes when the charge was exploded, filling the
hostile mine with deadly fumes that would suffocate miners working the
gallery and prevent the gallery from being re-entered by hostile miners.
Its destructive effect on the gallery itself was supposed to be negliable so
that the mine gallery from which the camouflet was exploded would not suffer
serious damage and could continue in use."