  the m197 electric cannon is a three-barreled electric gatling-type rotary cannon used by the united states military. ==development== the m197 electric cannon' developed primarily for use by united states army helicopter gunships. development began in 1967 after experience in the vietnam war revealed the inadequacy of the 7.62&nbsp;mm minigun for gunship use. the m197 is essentially a lightened version of the general electric m61 vulcan cannon, with three barrels instead of six. its maximum rate of fire is one quarter that of the vulcan, largely to limit its recoil for light aircraft and helicopter use. it shares the vulcan's m50 and pgu series 20&nbsp;mm ammunition. ==history== the m197 went into service on later marks of the ah-1 cobra, using either the m97 or a/a49e-7 armament subsystems, and was also fitted in a ventral turret on the u.s. marine corps yov-10d bronco nogs. it is also the basis of the gpu-2/a gun pod, which incorporates the cannon, a battery and electric drive motor, and 300 rounds of linkless ammunition. in the cobra, the weapon is supplied with a magazine of 700 linked rounds, with a total capacity including feeder system of 750 rounds. it has a cyclic rate of fire of 650 rounds per minute. standard practice is to fire the cannon in 30 to 50-round bursts. the m197 remains in use in the latest ah-1w cobra and ah-1z viper gunships. although the weapon's rotary drive is theoretically quite reliable, its ammunition feed has been anything but: marine pilots initially reported an alarmingly high jam rate (sometimes greater than 30%). the usmc and the manufacturer are aware of the problem and in 2011 a link less feed system developed by meggit defense systems was incorporated into the ah-1w and the zulu's. the system is capable of holding 650 +/-3 rounds in the storage unit with approximately 40 rounds in the feed chute. the m197 is also mounted as a chin 
20_mm_artillery Aircraft_guns Multi-barrel_machine_guns Rotary_cannons United_States_Marine_Corps_equipment