prevented more conversions. It was returned to the United States, and the program stopped. The ACH-47A carried five 7.62 × 51 mm M60D machine guns or .50-caliber (12.7 mm) M2HB heavy machine guns, provided by the XM32 and XM33 armament subsystems, two 20 mm M24A1 cannons, two 19-tube Folding Fin Aerial Rocket launchers (XM159B/XM159) or sometimes two M18/M18A1 7.62 × 51 mm gun pods, and a single 40 mm M75 grenade launcher in the XM5/M5 armament subsystem (more commonly seen on the UH-1 series of helicopters). Rare newsreel footage shows one of the aircraft in action supporting the 8th Cavalry Regiment during an ambush at Bông Son, South Vietnam. The surviving aircraft, Easy Money, has been restored and is on display at Redstone Arsenal, Alabama. CH-47B The CH-47B was an interim solution while Boeing worked on a more substantially improved CH-47C. The CH-47B was powered by two Lycoming T55-L-7C engines. It featured a blunted rear rotor pylon, redesigned asymmetrical rotor blades, and strakes along the rear ramp and fuselage to improve flying characteristics. It could be equipped with two door-mounted M60D 7.62 mm NATO machine guns on the M24 armament subsystem and a ramp-mounted M60D using the M41 armament subsystem. Some CH-47 "bombers" were equipped to drop tear gas or napalm from the rear cargo ramp onto Viet Cong bunkers. The CH-47B could be equipped with a hoist and cargo hook. The Chinook proved especially valuable in "Pipe Smoke" aircraft recovery missions. The "Hook" recovered about 12,000 aircraft valued at over $3.6 billion during the war; 108 were built. CH-47C The CH-47C principally featured more powerful engines and transmissions. Three sub-versions were built; the first had Lycoming T55-L-7C engines delivering . The "Super C" included Lycoming T55-L-11 engines delivering , an upgraded maximum gross weight of , and a pitch stability augmentation system. The T55-L-11 engines suffered difficulties, as they had been hurriedly introduced to increase payload; thus, they were temporarily replaced by the more reliable Lycoming T55-L-7C. The type was distinguishable from the standard "C" by the uprated maximum gross weight. The type was unable to receive FAA certification to engage in civil activities due to the nonredundant hydraulic flight boost system drive. A redesign of the hydraulic boost system drive was incorporated in the succeeding CH-47D, allowing that model to achieve certification as the Boeing Model 234. A total of 233 CH-47Cs were built. Canada bought a total