Gunboat A gunboat is a naval watercraft designed for the express purpose of carrying one or more gun s to bombard coastal targets , as opposed to those military craft designed for naval warfare , or for ferrying troops or supplies . History . In the age of sail , a gunboat was usually a small undecked vessel carrying a single smoothbore cannon in the bow , or just two or three such cannon s . A gunboat could carry one or two masts or be oar - powered only , but the single - masted version of about length was most typical . Some types of gunboat carried two cannons , or else mounted a number of swivel gun s on the railings . The advantages of this type of gunboat were that since it only carried a single cannon , that cannon could be quite heavy — for instance , a 32 - pounder — and that the boat could be maneuvered in shallow or restricted waters , where sailing was difficult for larger ships . A single hit from a frigate would demolish a gunboat , but a frigate facing six gunboats in an estuary would likely be seriously damaged before it could manage to sink all of them . Gunboats were also easy and quick to build ; the combatants in the 1776 Battle of Valcour Island on Lake Champlain in New York were mostly gunboats built on the spot . All navies of the sailing era kept a number of gunboats on hand . Gunboats saw extensive use in the Baltic Sea during the late 18th century as they were well - suited for the extensive coastal skerries and archipelagoes of Sweden , Finland and Russia . The rivalry between Sweden and Russia in particular lead to an intense expansion of gunboat fleets and development of new gunboat types . The two clashed during the Russo - Swedish war of 1788 - 90 a conflict that culminated in the massive Battle of Svensksund in 1790 , where over 30 , 000 men and hundreds of gunboats , galley s and other oared craft participated . The majority of these were vessels developed from the 1770s and onwards by the naval architect Fredrik Henrik af Chapman for the Swedish Archipelago Fleet . The designs were copied and refined by the rival Danish and Russian navies and spread to the Mediterranean and the Black Sea . Two variants were the most common , a larger " gun sloop " ( from the Swedish " kanonslup " ) with two 24 - pounders , one in the stern and one in the bow , and a smaller " gun yawl " ( " kanonjolle " ) with a single 24 - pounder . Many of the Baltic navies kept gunboats in service well into the second half of the 19th century . British ships engaged larger Russian gunboats off Turku in southeast Finland in 1854 during the Crimean War . The Russian vessels had the distinction of being the last oared vessels of war in history to fire their guns in anger . Gunboats were a key part of Napoleon ' s plan for the invasion of England in 1804 . Denmark - Norway used them heavily in the Gunboat War . Between 1803 and 1812 , the United States Navy had a policy of basing its navy on coastal gunboats . It experimented with a variety of designs , but they were nearly useless in the War of 1812 , and went back to being special - purpose vessels . Steam era . With the introduction of steam power in the early 19th century , the Royal Navy and other navies built considerable numbers of small vessels propelled by side paddles and later by screw s . Initially , these vessels retained full sailing rigs , so that steam propulsion was used as an auxiliary form . The British Royal Navy deployed two wooden paddle gunboats in the Lower Great Lakes and St . Lawrence River during the Rebellions of 1837 in Upper and Lower Canada . The United States Navy deployed an iron - hulled paddle gunboat , the USS Michigan , to the Great Lakes in 1844 . The " Von der Tann " was the first propeller - driven gunboat in the world . Conradi shipyards in Kiel built the steam - powered gunboat in 1849 at for the small navy of Schleswig - Holstein . Initially called " " Gunboat No . 1 " " , " Von der Tann " was the most modern ship in the navy . She participated successfully in the First Schleswig War . Britain built a large number of wooden screw gunboats during the 1850s , some of which participated in the Crimean war , Second Opium War and Indian Mutiny . The requirement for gunboats in the Crimean war was formulated in 1854 and was to allow for shore bombardment operations to be carried out in the Baltic . The first ships the Royal Navy built that met this requirement were the " Arrow " - class gunvessels . Then in mid - 1854 the Royal Navy ordered six " Gleaner " - class gunboats followed latter in the year by an order for 20 " Dapper " - class gunboats . In May 1855 , six " Dapper " - class gunboats were deployed to the Sea of Azov where they repeatedly raided and destroyed stores around its coast . In June 1855 , the Royal Navy reentered the Baltic with a total of 18 gunboats as part of a larger fleet . The boats were used to attack various coastal facilities operating alongside larger warships from which they drew supplies such as coal . Gunboats experienced a revival during the American Civil War . Armed sidewheel steamers were quickly converted from existing passenger - carrying boats by Union and Confederate forces . Later , some boats were purposely built , such as the . They all frequently mounted 12 or more guns , sometimes of rather large caliber , and were usually armored to some degree . At the same time , Britain ' s gunboats from the Crimean war period were starting to wear out so a new series of classes was ordered . At the same time , construction shifted from a purely wooden hull to an iron teak composite . In the later 19th century and early 20th century , " gunboat " was the common name for smaller armed vessels , often called " patrol gunboats " . These could be classified , from the smallest to the largest , into river gunboat s , river monitor s , coastal defense gunboats ( such as the ) , and full - fledged monitors for coastal bombardments . In the 1870s - 1880s , Britain took to building so called " flat - iron " ( or Rendel ) gunboat s for coastal defence . When there would be few opportunities to re - coal , vessels carrying a full sailing rig were still used as gunboats ; , a sloop preserved at Chatham Historic Dockyard in the United Kingdom , is an example of this type of gunboat . In the U . S . Navy , these boats had the hull classification symbol " PG " ; they usually displaced under , were about long , draught and sometimes much less , and mounted several guns of caliber 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 , gunboats were used by the naval powers for police actions in colonies or weaker countries , for example in China ( see e . g . Yangtze Patrol ) . It is this category of gunboat that inspired the term " gunboat diplomacy " . With the addition of torpedoes they became " torpedo gunboat s " . In Britain , much of the gunboat fleet was disposed of as part of Admiral Fisher ' s reforms in the 1900s . A handful were still in service in various roles at the start of World War I . The very last in active service were two of the second " Bramble " class which survived until 1926 carrying out river patrols in west Africa . In the circumstances of World War I , however , the Royal Navy re - equipped with small ( ) , shallow draught gunboats ( 12 ships of the Insect class ) with sufficient speed to operate in fast - flowing rivers and relatively heavy armament . During the War and in the post - war period , these were deployed in Romania on the Danube , in Mesopotamia on the Euphrates and Tigris , in northern Russia on the Northern Dvina and in China on the Yangtze . In China , during anarchic and war conditions , they continued to be deployed until World War II in defence of British interests ; other western Powers did the same . More , larger , gunboats were built in the late 1930s for the Far East . Some were sailed there ; others were transported in sections and reassembled at Shanghai . World War II and the United Kingdom . Most British gunboats were withdrawn from the Far East early in World War II and redeployed in the Indian Ocean and the Mediterranean , where they supported various army operations in north Africa and southern Europe . Those that remained in the Far East were either handed over to the Chinese ( HMS " Sandpiper " , renamed " Ying Hao " ) or lost to the Japanese . Vietnam War . U . S . riverine gunboats in the Vietnam War , utilized Patrol Boats River ( PBR ) , which were constructed of fiberglass ; Patrol Craft Fast ( PCF ) , commonly known as Swift Boats , which were built of aluminum ; and Assault Support Patrol Boats ( ASPB ) built of steel . U . S . Coast Guard 82 - foot Point class cutter s supplemented these U . S . Navy vessels . The ASPBs were commonly referred to as " Alpha " boats and were primarily deployed for mine sweeping duties along the water ways , due to their all steel construction . The ASPB ' s were the only U . S . Navy riverine craft specifically designed and built for the Vietnam War . All of these boats were assigned to the U . S . Navy ' s " Brownwater Navy " .