Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. 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.