What was the US Navy's small river patrol boat widely used in the Mekong Delta called?

The U.S. Navy’s small river patrol boat widely used in the Mekong Delta was called the Patrol Boat, River, or PBR.

The PBR was a shallow-draft, rigid-hulled craft designed for patrol and interdiction on Vietnam’s waterways. Beginning in 1966, PBR crews stopped and searched river traffic, looking for weapons and personnel moving through the Mekong Delta, the Rung Sat Special Zone, and the Saigon River. Their jet-pump propulsion allowed them to maneuver in shallow water without exposed propellers.

PBRs served primarily with the River Patrol Force, Task Force 116. Crews commonly carried .50-caliber machine guns and other weapons, and the boats also transported or supported Navy SEAL teams. Their speed and flexibility made them central to the U.S. riverine campaign, though they were vulnerable to ambushes from riverbanks and concealed enemy positions.

The name is often shortened to PBR or pronounced “Pibber.” It should not be confused with a Patrol Craft Fast, the larger coastal patrol boat commonly known as a Swift boat.