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.

[1][2] 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.

[3] 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".

[5] Subtle forces therefore covered a wide variety of vessels and boats, like gunboats, feluccas, xebecs, pontoons, barges, brigantines, fireships, skiffs, pataches, tartanes, zumacas and the increasingly rare galleys and galiots.

According to him, Spanish gunboats dealt constant, unanswered damage due to their size and number,[9] as British artillerymen couldn't sight them by night and found out it was similarly useless to aim for their gun flashes.