Gunboat
In the United States Navy, these boats had the hull classification symbol "PG", which led to their being referred to as "patrol gunboats". They usually displaced under , were about  long,  draught and sometimes much less, and mounted several guns of calibers up to . An important characteristic of these was the ability to operate in rivers, enabling them to reach inland targets in a way not otherwise possible before the development of aircraft. In this period the naval powers used gunboats for police actions in colonies or in weaker countries, for example in China (see e.g. Yangtze Patrol). This category of gunboat inspired the term "gunboat diplomacy". With the addition of torpedoes, they became "torpedo gunboats", designated by the hull classification symbol "PTG" (Patrol Torpedo Gunboat).