What were the armed ACH-47As nicknamed?

Before receiving its official designation, the aircraft was known as the Armed/Armored CH-47A (A/ACH-47A). The US Army later designated it ACH-47A, attack and cargo helicopter, but unofficially it was known by a nickname: "Guns A Go-Go."

Boeing Vertol converted four CH-47As into gunships in late 1965. They received armor and upgraded engines, and an extremely heavy armament for a helicopter: two fixed forward-firing 20 mm M24A1 cannons, a nose turret with an automatic 40 mm grenade launcher, five 12.7 mm (.50 cal) machine guns and two side pods for additional weapons. Three were assigned to the 53rd Aviation Detachment in South Vietnam, and the fourth remained in the United States for weapons testing.

They arrived in Vietnam in 1966 and completed six months of operational evaluation at An Khe airfield. In 1966 the 53rd was renamed the 1st Aviation Detachment (Provisional) and was absorbed into the 228th Assault Support Helicopter Battalion of the 1st Cavalry Division (Airmobile). The ACH-47As performed well in combat, but they were expensive to maintain, and the Army needed its Chinooks more for moving troops and cargo. Three were lost: one collided while taxiing with another CH-47, another crashed when its own cannon fire struck the forward rotor blades, and the third was destroyed after being pinned down by enemy fire.

The nickname contrasted with the Chinook's usual role in Vietnam, which was mostly logistical and highly risky: of nearly 750 Chinooks in the US and South Vietnamese fleets, around 200 were lost in combat or in wartime operational accidents.