>>According to the Vietnam Helicopter Pilots Association, a total of 11,846 helicopters were shot down or crashed during the war
В этой цитате, скорее всего, какая-то "накладка", поскольку на сайте самой VHPA оно озвучивается так:
Helicopter Losses During the Vietnam War
Updated 31 December 2018
There were about 12,000 helicopters that served in the Vietnam War (the VHPA has specific tail
numbers for 11,846 from all services). We have records showing 5,607 helicopter losses or about half.