noun
patrol boat; guard boat; guardship
A small vessel used for security, patrol, or guard duties, often by coast guard, police, or military forces.
沿岸警備隊の警備艇が不審船を追跡した。
The coast guard's patrol boat pursued the suspicious vessel.
警備艦 refers to a larger guard ship or escort vessel, whereas 警備艇 is a smaller boat.
Compound of 警備 (けいび, 'security, guard') and 艇 (てい, 'small boat').