The H-21 "Flying Banana", which was originally designed by Piasecki for cold weather operations, performed poorly in the hot weather of Vietnam. Despite being capable of carrying 20 passengers, it could lift only nine when operating there, the engines achieving less than half the standard 600 hours between major overhaul. Despite that, it soldiered on as the US Army's main helicopter workhorse in Vietnam until 1964 when replaced with the Bell UH-1 Huey

Preserved at the US Army Aviation Museum from 1970.