High Quality Content by WIKIPEDIA articles! A river gunboat is a type of gunboat adapted for river operations. River gunboats required shallow draft for river navigation. They would be armed with relatively small caliber cannons, or a mix of cannons and machine guns. If they carried more than one cannon, one might be a howitzer, for shore bombardment. They were usually not armoured. The USS San Pablo described in Richard McKenna`s The Sand Pebbles is an example of this class of vessel, serving on the US Navy`s Yangtze Patrol. Stronger river warships were river monitors.