RivSec 531

**RivSec 531**, officially known as Riverine Security Unit 531, was established in 1967 as part of the U.S. Navy’s Mobile Riverine Force during the Vietnam War. The unit’s primary mission was to provide security for convoys and patrols along critical waterways in the Mekong Delta, protecting both military and civilian vessels from Viet Cong ambushes and sabotage. RivSec 531 crews operated heavily armed Patrol Boat, River (PBR) craft, engaging in frequent firefights and conducting boarding operations in challenging, jungle-lined rivers. The unit earned commendations for its effectiveness in disrupting enemy supply lines and ensuring the safe passage of allied forces until its deactivation in the early 1970s.