US Army handout file photo showing a CH-47F Chinook helicopter landing at Camp Marmal in Mazar-e Sharif province. Thomson Reuters With two 20mm cannons, a 40mm automatic grenade launcher, five .50-caliber machine guns, and two weapon pods that could carry either 70mm rocket launchers or 7.62mm miniguns, the armored ACH-47A Chinook could fly into the teeth of enemy resistance and fly back out as the only survivor.

The aircraft boasted overlapping fields of fire and 360-degree coverage.

Operating under the call sign "Guns-A-Go-Go," these behemoths were part of an experimental program during Vietnam to create heavy aerial gunships to support ground troops. Four CH-47s were turned into ACH-47As by adding 2,681 pounds of armor and improved engines to each bird.

The first three birds arrived in Vietnam in 1966, and they engaged in six months of operational testing. They were assigned to support the US Army's 1st Cavalry Division as well as a Royal Australian Task Force.

The Army Pictorial Service covered an early mission flown in support of the Australians in which the attack Chinooks were sent to destroy known enemy positions.