In 1965 during the Vietnam War the outstanding load capacity of the CH-47 Chinook led the U S Army to request a heavily armed version in order to provide support for the AH-1 Cobra The first flight took place on 6th November of the same year & in May 1966 four examples of these heavy Chinooks assigned to the 1st Air Cavalry Division were stationed at the An Khe base for trials Thanks to heavy armaments including a 40 mm XM-5 grenade launcher two 20 mm M-24 cannon five 12 7 mm M-2 machine guns & two hook-up points for rocket launchers or other loads-plus heavy armour to shield both crew & helicopter-the ACH-47 proved highly effective in a ground troop support role Nevertheless because of the complexity of the aircraft & the pressing need for transport versions of the Chinook the U S Army halted any further development