 On 17 August 1972 , the Army initiated the Advanced Attack Helicopter ( AAH ) program . AAH sought an attack helicopter based on combat experience in Vietnam , with a lower top speed of 145 kn ( 167 mph , 269 km / h ) and twin engines for improved survivability . Lockheed offered the CL @-@ 1700 , a modified version of the Cheyenne with two engines and omitted the pusher propeller , without success . The AAH program led to the AH @-@ 64 Apache , which entered service in the mid @-@ 1980s . 
