A gunboat is a small watercraft armed with one or more guns for the purpose of bombarding coastal targets or harassing larger warships. In the 18th century, European naval forces like the Royal Navy, the Spanish Navy, French Navy, and the Portuguese Navy all included gunboats in their fleets to support their capital ships. 
From the War of Spanish Succession to the Seven Years' War and the American Revolutionary War, the gunboat was used as a quick response attack vessel by not only the navies but civilian operators as well. This was due to its extremely simple design that required very little crew. This lightly armed vessel provided ample speed and a quick rate of fire, with the trade-off being that it bore next-to-no armor whatsoever. Each ship was composed of a single mast and a sleek, low hull, and was capable of fielding just two frontal guns, capable of shooting both the standard round shot and the wide-spray grapeshot.
Due to their sparse protection and tiny profile, gunboats were highly vulnerable to ramming by larger vessels like frigates, brigs or Men O' War, almost always being instantly rent asunder by their bows. Single shots from swivel guns would be enough to destroy any gunboat of this era. Their sole function was to act as the naval equivalent of skirmishers, carrying little to no cargo other than ammunition. While fragile and weak in firepower, a common tactic by navies in an age where watercraft were made from wood was to convert these gunboats into fireships which were then sent careening into large enemy ships in the hope of setting them aflame.