River monitors were heavily armored, and normally mounted the largest guns of all riverine warships. The name originated from the US Navy's Brown Water Navy's USS Monitor, which made her first appearance in the American Civil War, and being distinguished by a single revolving turret.

On 18 December 1965, the US Navy, for the second time in one hundred years, authorized the reactivation of a Brown Water Navy for riparian operations in South Vietnam. In July 1966, Secretary of Defense Robert S. McNamara authorized the formation of a Mobile Riverine Force (MRF);[1] a force, that would bring back the heavily armored single turret River Monitor.

River monitors were used on inland waterways such as rivers, estuaries, deltas and lakes. Usually they had a shallow draft which was necessary for them to be able to operate in enclosed waters; but their displacement, size and draft varied depending on where they were used.

Most river monitors were lightly armored although this varied, with some carrying more armor. Exceptional examples, however, most notably the Royal Navy's Lord Clive Class monitors, which could operate in coastal or certain riparian/esturine situations, bore extra-thick armor plating and heavy shore-bombardment guns, up to a massive 18-inches (457 mm) in size. Typically, however, river monitors displayed a mixture of gun sizes from 3-inch (75 mm) to 6-inch (152 mm), plus machine guns. This type of vessel overlaps with the river gunboat.

United StatesEdit

During the Vietnam War, the US Navy's Brown Water Navy, operated its Monitors as part of their River Assault Flotilla One, which "initially" consisted of four River Assault Divisions (RAD); with RAD 91 containing 3 Monitors, RAD 92 having 2 Monitors, RAD 111 having 3 Monitors, and RAD 112 operating 2 Monitors.[2]

The Vietnam Monitors were divided into two programs; program 4 would consist of the 40mm gun Monitors, while the later program 5 would entail the eight Monitor (H) Howitzer versions, and the six Monitor (F) Flamethrower models.[3] All of the Monitors were converted from World War II 56' long all steel Landing Craft Mechanized (LCMs) Mk 6's.[4] When completed, they were 60' long, 17' wide, with a draft of 312', had two screws driven by two Gray marine model 64NH9 diesel engines, could do 8.5 knots and were manned by usually 11 or more crewmen.[5] The fielded Monitors normally averaged about ten tons of armor on them.

US riverboat using napalm in Vietnam

A Mobile Riverine Force monitor using napalm in the Vietnam War.[6]

USN Brown Water Navy River Monitors (Vietnam)[7]
Generation-One Type Generation-Two Type/Flame Generation-Two Type/Howitzer
Length 61 ft. 60 ft. 6 in.
Width 17 ft. 6 in.
Draft 3 ft. 6 in.
Engines 2 × 64HN9 Diesels; 220 hp @ 2100 rpm
Speed 8.5 knts
Crew 11
  • 2 × 20 mm cannons
  • 2 × 200m flame throwers
  • 3 × M79 grenade launchers
  • 2 × 50 cal. machine guns
  • 1 × 105 mm howitzer
  • 2 × 20 mm cannons
  • 3 × M79 grenade launchers
  • 2 × 50 cal. machine guns
  • 1 × 7.62 mm machine gun


  1. Carrico, p. 11
  2. Carrico, p. 12
  3. Carrico p. 63
  4. Carrico, p. 16, 17
  5. Carrico, p. 63
  6. Carrico p. 82
  7. Monitor Specifications, U.S. Navy Mobile Riverine Force,