Fuerzas sutiles
Fuerzas sutiles ("subtle forces") was an 18th century term, used in the Spanish Empire and its successor states, referring to the strategic usage of small vessels in naval warfare. This included gunboats, xebecs and armed feluccas, originally used to defend ports before being re-purposed to offensive tactics, escorting convoys and operate in seas and rivers.
The concept was popularized by captain Antonio Barceló, after which the Spanish Armada developed it extensively and with great efficacy, turning subtle forces into what has been described as "sea guerrillas". This kind of naval warfare would be known in France as flotilles a l’espagnole ("Spanish-style flotillas").